DOMESTIC EXTENSIONS & GARAGES

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B
UILDING





BUILDING CONTROL

GUIDANCE

FOR

DOMESTIC EXTENSIONS

& GARAGES


Extensions upto 2 storeys with

additional guidance for 3 storeys











JUNE

2011: Amendment 2





Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


2

CONTENTS












PAGE NUMBER

Intr
oduction











7

Approved Documents and sections they cover

Other guidance documents available

1.0 Engaging a property professional







8

2.0 Obtaining Building Regulations approval

2.1 Full Plans application

2.2 Building Notice application

3.0 Exemp
t buildings and work








9

4.0 Competent Person Scheme

5.0 Planning Permission, listed building & conservation area consents

6.0 The Party Wall Act 1996









10

7.0 Rights of light










11

8
.0 Construction (Design and Management) Regulations 2007

(CDM)



12

9
.0 Protection of Bats

10
.0 Preliminaries for preparation, protection, access and demolition



13

1
1
.0 Technical & practical guidance for domestic extensions




14

Part A: Structure

A1: Sub structure

Foundations (including retaining walls & b
asements)

Strip foundations

Diagram 1: Strip foundation section detail

Trench fill foundations

Diagram 2: Trench fill foundation section detail

Alternative foundation designs









15

Sub structure

Diagram 3: Stepped foundation section detail

Ground
bearing solid concrete floors








1
6

Diagram 4: Typical section through a ground bearing solid concrete floor

& foundation.

Suspended reinforced in
-
situ concrete ground floor slab supported on internal walls


17

Diagram 5: Typical section through a
suspended reinforced in
-
situ concrete ground

floor slab supported on internal walls.

Suspended beam & block ground floors








1
8

Diagram 6: Typical section through a suspended beam & block ground floor

Table 1: Ground bearing slab & suspended beam &
block ground

floor insulation requirem
ents

19

Floating floor

Table 2: Floating floor insulation requirements

Suspended timber ground floor









20

Diagram 7: Typical section through a suspended timber ground floor

Table 3: Suspended timber ground floo
r insulation requirements





21

Garage ground bearing concrete floor

Diagram 8: Typical section through a ground bearing garage floor & foundation



22

A2: Superstructure










23

External walls

Cavity walls

Table 4: Partial cavity fill insulation r
equirements for external cavity walls

Table 4.1: Full cavity fill insulation requirements for external cavity walls




24

Walls between heated and un heated areas

Table 5: Insulation requirements to solid walls between heated & un heated areas

External
timber framed walls with render finish

Diagram 9: Typical section through external timber framed walls with painted render finish

25

External timber framed walls with cladding finish

Diagram 10: Typical section through external timber framed walls with
upvc/timber

weather board finish

Detached garage with SINGLE SKIN external walls






26

Diagram 11: Design criteria for small detached single storey garages or similar

Wall abutments











27

Lintels & weep holes

Structural columns/beams etc

Expans
ion joints

Strapping and restraint

Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


3

Cavity Closers

A3: Separating walls & floors









28

M
asonry party walls separating dwellings

Diagram 12: Section detail of masonry separating wall as Wall type 2.1 of

Double leaf timber frame party walls separatin
g buildings

Diagram 13: Plan detail of timber stud separating wall as Wall type 4.1

Upgrading sound insulation of existing separating walls






29

Diagram 14: Plan of upgrading masonry separating wall as Wall type 4.2

Party floors separating building
s

Sound testing requirements

A4: Additional provisions for 3 storey buildings/extensions





30

Compressive strength of masonry units

A5: Internal partitions

Internal load bearing masonry partitions

Internal load bearing timber stud partitions

Internal mas
onry non
-
load bearing partitions

Internal timber studwork non
-
load bearing partitions

A6: Intermediate upper floor(s)








31

Floor Joists

Table 6: Spans for Common Domestic Floor Joist Sizes (Strength Class C24)

Trimming/trimmer/trimmed joists

Table 7:

Spans for Common Trimmer Joist supporting Trimmed Joists

Table 8: Spans for Common Trimming Joist supporting Trimmer Joist




32

Diagram 15: Typical plan layout of opening formed in upper floor(s)

Notches / holes/cuts in structural timbers

Sound insula
tion to floors within the dwelling







33

SVP pipe boxing

Exposed intermediate upper floors

Diagram 16: Typical section through an upper floor

Table 9: Insulation requirements to exposed upper floors

A7: Pitched roofs










34

Pitched roof coverings


Pitched roof structure

Roof trusses (including attic & girder trusses)

Cut roof construction

Notches / holes/cuts in structural timbers







35

Diagram 17: Typical section through pitched roof with ceiling joists at wall plate level

Diagram 18: Typical

section through a pitched roof with purlins & high collars



36

Table 10: Spans for Common Domestic Timber Rafter Sizes

Table 11: Spans for Common Domestic Timber Ceiling Joist Sizes

Table 12: Spans for Common Domestic Timber Purlin Sizes





37

Table
13: Permissible Clear Spans for Common Ceiling Binders Sizes

Roof restraint

Roof insulation & ventilation gaps

Table 14: Insulation fixed between/under rafters

Table 15: Insulation laid horizontally between and over ceiling joists




38

Table 16: Insulat
ion fixed between/over rafters

Diagram 19: Typical section through a dormer roof

Diagram 20: Typical roof valley detail








39

Roof ventilation to pitched roofs with non breathable roofing felt

Roof with horizontal ceilings & insulation at wall plate

level

Pitched roof with insulation following slope of rafters & mono pitched roofs

Breathable roof membranes

A8: Flat roof construction









40

Table 17: Spans for Common Flat Roof Joist Sizes






41

Table 18: Insulation Fixed Between/Under Flat Roof

Joists

Table 19: Insulation Fixed above Flat Roof Joists

Valleys and lead work

Lofts hatches, doors & Light wells to roof spaces

Diagram 21: Typical section through a flat (cold) roof






42





Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


4

Part B: Fire safety & means of escape







43

Smoke /he
at alarms

Means of escape windows

Fire doors & frames

Means of escape from basements

Permitted building openings in relation to a boundary:

Openings within 1.0m of a boundary

Openings more than 1.0m from a boundary

Table 20: Permitted unprotected areas in
relation to a relevant boundary

Fire resistance to elements of structure etc







44

Table 21: Fire resistance to common elements of structure etc

Surface spread of flame: wall & ceiling linings

Table 22: Surface spread of flame: Classification of wall &
ceiling linings

Additional fire safety & means of escape provisions for 3 storey buildings/ extensions

Residential sprinkler systems for means of escape






45

Part C: Site preparation and resistance to contaminants & moisture

C1: Resistance to contamin
ants








46

Radon gas

Protective measures against radon gas

Construction methods required to limit the infiltration of radon into buildings

1. Basic radon protection

2. Full radon protection










47

Sumps and subfloor depressurisation

Number & posi
tion of sumps

Diagram 22: Plan layout of sump and depressurization pipe positions in two different

building sub structures

Sump construction

(i) Site constructed sumps

(ii) Proprietary prefabricated sumps

Depressurisation pipes










48

(iii) Geo
-
text
ile drainage matting


(iv) Edge
-
located sumps

Radon fan locations

Stepped foundations & retaining walls

Further details

Methane & other gas protection in sub structure







49

Landfill gas and radon

C2: Resistance to moisture

Horizontal damp proof cours
es & trays

Vertical damp proof courses & trays etc

Tanking systems to walls

Flood risk

Part D: Cavity wall filling with insulation







50

Part E: Resistance to the passage of sound






51

New Internal walls & floors in new extension

New party wall
s and floors in new extension

Pre completion sound testing

Remedial works and re
-
testing

Part F: Ventilation










52

Purge (natural) ventilation

Mechanical extract ventilation & fresh air inlets for rooms without purge ventilation

Background ventil
ation

Mechanical extract ventilation rates

General requirements for mechanical extract ventilation

Part G: Sanitation, hot water safety and water efficiency




53

Wholesome water supply

Safety valves & energy cut outs

Wash basins & separation of w/c from a
ny food preparation areas

Water tanks/cisterns base

Pumped small bore foul water drainage

Commissioning certificates

Supply (Water Fittings) Regulations 1999


Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


5

Part H: Drainage and waste disposal







54

H1: Foul water drainage

Foul, rain & storm wate
r drainage systems

Waste pipes

H2: Septic tanks, sewage treatment systems & cesspools





55

Existing septic tank & effluent drainage

Non mains foul drainage waste water treatment systems

Septic tanks

Sewage treatment systems









56

Treatment of sewage

from septic tanks & sewage treatment systems

Drainage fields

Drainage mounds

Wetlands/reed beds










57

Percolation test method to calculate area of drainage field for septic tanks

or sewage treatment systems.

Diagram 23: Typical section through a

septic tank/treatment system drainage field


58

Diagram 24 : Typical drainage field plan layout

H3: Rainwater drainage and harvesting







59

Rainwater gutters and down pipes

Table 23: Gutter sizes & pipe outlet sizes for drainage of roof are
as

Rainwater/ grey water harvesting storage tanks & systems

Surface water drainage around the building

Oil/fuel separators

H4: Building over or close to public sewers







60

H5: Separate systems of drainage

H6: Solid waste storage

Part J: Combustion appl
iances & fuel storage systems




61

Space & hot water heat producing appliances in general

Solid fuel appliances up to 50kW rated output


Construction of open fire place with recess & hearth


Free standing stove with hearth


Air supply (ventilation) to s
olid fuel appliances


Table 24:

Air supply (ventilation) to solid fuel appliances






62

Carbon monoxide alarms


Table 25: Sizes of flues in chimneys

Construction of masonry chimneys








63



Construction of factory made flue block chimneys


Construc
tion of factory made insulated metal chimneys


Configuration of flues serving open flue appliances

Single flue pipes & protection of combustible material

Diagram 25: Free standing stove & metal chimney detail through a building



64

Inspection & cleanin
g openings in flues

Single flue pipes & protection of combustible material

Interaction of mechanical extract vents & opened flue solid fuel appliances




65

Chimney heights

Repair/relining of existing flues


Notice plates for hearths & flues

Appliances ot
her than solid fuel

Interaction of mechanical extract vents & opened flue combustion appliances

Gas appliances

Oil appliances

Gas heating appliances up to 70kw


Oil heating appliances up to 45kW








66

Renewable energy Installations

Provision of informa
tion
-

commissioning certificates

Fuel storage tanks

LPG tanks and cylinders up to 1.1 tonnes

Oil tanks up to 3500 litres

Part K: Protection from falling, collision and impact





67

Internal stairs, landings and changes in level of 600mm or more

Diagram

26:
Measuring rise & goings

Diagram 27:
Typical internal stair case & guarding construction details




68

External stairs, landings and changes in level of 600mm or more

External stairs & landings

Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


6

External guarding

Guarding to upper storey window openi
ngs/other openings within 800mm of floor level


Part L: Conservation of fuel and power in existing dwellings




69

Listed buildings, conservation areas & ancient monuments

Areas of external windows, roof windows & doors

New thermal elements

External gl
azing

Table 26: U
-
value requirements for external windows & doors including roof windows

Table 27: U
-
values for double glazing

Table 28: U
-
values for triple glazing
-

Pilkington EnergiKare glazing system



70

Closing around window & door openings

Sealing &

draught proofing measures

External Walls, roofs, floors & swimming pool basin

Table 29: U
-
values for external walls, roofs, floors & swimming pool basin

Renovation/upgrading of existing thermal elements

Table 30: Renovation/upgrading of existing thermal
elements

Payback report











71

Energy efficient lighting

Fixed internal lighting

Fixed external lighting

Consequential improvements

Commissioning of fixed building services

Providing information
-
building log book

Part M: Access to and use of build
ings for disabled





72

Part N: Safety glazing, opening & cleaning







Safety glass and glazing

Diagram 28: Glazing in windows, partitions, doors, side panel/screens and walls

Part P: Electrical safety









73

Electrical Installations

External wo
rks
-

paths, drives, patio & gardens

Materials and workmanship

Acknowledgements:

Guidance notes copyright









74

Important note:

Additional building control services we can provide

Gloucestershire district council building control contact details


Usef
ul numbers of other agencies or companies






75




















Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


7

Introduction

This document intends to provide education and guidance on how some of the technical design
and construction requirements of the Building Regulations 20
10

can be achieved and
met for
new extensions to dwellings up to two storeys in height and within 4.5m of ground level and
additional guidance is given for three storeys in height which has a floor 4.5m above ground level

and garages
.


In all cases the design and construction of

the proposed works is the responsibility of the
designer, applicant and contractor and should be carried out to the relevant submitted and
approved design. For further information reference should be made to the relevant Approved
Document or standard as w
ell as consulting a suitably qualified and experienced construction
professional.


The Approved Documents, which are listed below are available to view on
the Communities and
Local Government web site
:
www.
communities
.gov.uk

or to purchase from The Station
ary Office
(TSO) on line at
www.tsoshop.co.uk

or telephone: 0870 600 5522.


However, the Building Regulation requirements may be satisfied in other ways or non
-
standard
ways by calculations or test details from a m
anufacturer or an approved 3rd party method of
certification such as BBA (British Board of Agreement) Certificate.


This document can be made available on a range of other formats if required. For further
information please contact us on 01594 810000
.


Ap
proved Do
cuments and sections they cover:

A:

Structure (2004 edition) including TRADA
Euro S
pan
T
ables for solid timber

members in floors, ceilings and roofs for dwellings (
3rd

edition 200
9
);

B1:

Fire safety in dwelling houses (2006 edition);

C:

Site

preparation and resistance to contaminants & moisture (2004 edition);

D:

Toxic substances (1992 with 2002 amendments);

E:

Resistance to the passage of sound (2003 with 2004 amendments);

F:

Ventilation (20
10

edition);

G:

Sanitation, hot water safet
y and water efficiency

(
2010

edition
);

H:

Drainage and waste disposal (2002 edition);

J:

Combustion appliances & fuel storage systems (20
10

edition);

K:

Protection from falling, collision and impact (1998 with 2002 amendments);

L1B:

Conservation of
fuel and power in existing dwellings (20
10

edition);

N:

Glazing


Safety in relation to impact, opening & cleaning (1998 with 2000 amendments);

P:

Electrical safety (2006 edition);

Regulation 7

Materials and workmanship (1992 with 2000 amendments).


Other guidance documents available
:

New Dwellings
;

Loft Conversions
; Conversion
of existing buildings, garages & basements into dwellings;
Commercial/

industrial buildings & Fire
Safety for Conversion of buildings into Holiday Lets, Guest Houses & Supervis
ed Groups with
Learning Difficulties.


Important note:

Typical section details have been provided in these guidance notes for the
more common construction methods used in dwellings. These details are suggested methods of
construction and are for guidance
only. You are advised to contact a suitably qualified and
experienced property professional for details and specifications for the most suitable form and
method of construction for your project.







Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


8

1.0 Engaging a
p
roperty
p
rofessional

Extensions are no
rmally complex projects and unless you are experienced in construction you

will need to get some professional advice
/help

from the following:

1. Appointing a suitably qualified and experienced property professional who will prepare

drawings and designs f
or your proposal, obtain the necessary approvals and if required

they will also help you to find a suitable builder and manage the project for you.


2. Appointing a specialist company who can offer a one stop shop for extensions, they can

prepare drawing
s and designs for your proposal, obtain the necessary approvals and carry out all

the necessary construction works to complete the project.

3. Using an experienced builder.


2.0 Obtaining Building Regulations approval

The building owner or agent must make

a building regulations application & pay a fee for the
construction of a new extension. All work must comply with the 20
1
0 Building Regulations and
the technical design and constructional requirements of the current Approved Documents A to P
and Regulatio
n
-

7 Materials and Workmanship.


The person carrying out the building works is to liaise with and meet the requirements of the LA
Building Control/Certifying Body, giving required notices of stages of works as required by the
Building Regulations includin
g:



Foundation excavations before any concrete is laid



Over site covering to ground floors before any concrete is laid



Foul & surface water drainage before any pipes are covered over



Structural timbers (upper storey floor joists/beams and roof structure bef
ore any coverings
are fixed



Completion of building
-
prior to occupation


There are two methods of making a Building Regulations application as follows:


2.1 Full Plans
a
pplication

This is often thought of as the traditional way of applying for Building Regu
lations Approval. The

building designer will draw up detailed plans and supporting information for the proposed scheme

and will send them to us together with a completed application form and the necessary fee which

are available to down load from our we
b site at:

www.fdean.gov.uk
. We will then check the

details and following any necessary consultations and liaisons with the building designer a

Building Regulations Approval will be issued.


Work can start any tim
e after the application has been received although it is wise to wait until

the scheme has had its initial check under the Building Regulations, this usually takes between

two and three weeks.


Our team of surveyors will liaise with your builder and insp
ect the work as it progresses on site.

When the project is satisfactorily completed a Building Regulations Completion Certificate will be

issued showing that the project has been independently inspected and that it complied with the

Building Regulations
.


2.2 Building Notice
a
pplication

This system is best suited to minor domestic work carried out by a competent builder. Under this

scheme no formal Approval of plans is issued and work is approved on site as it progresses.


To use the Building Notice pro
cess you or your agent will need to submit a completed

Building Notice application form together with a site location plan and the required fee
.


The application forms

are available to down load from our web site at:

www.fdean.gov.uk
.

W
ork can commence 48 hours after the notice has been received.





Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


9

When work commences one of our surveyors will meet with your builder to discuss your

intentions, to agree how the work should be carried out, agree when the work will

need to

be inspected and to establish whether any further information will be required
.


When the project is satisfactorily completed a Building Regulations Completion

Certificate will be issued showing that the project has been independently inspected
and

that it complied with the Building Regulations.


3.0
Exempt buildings and work

The following list is a brief extract of the more common building and works that are exempt the

building regulations, and for full details see Schedule 2 of the Building R
egulations 2010.



Green Houses & agricultural buildings
:
Buildings used for agriculture or keeping of animals
providing no part is used as a dwelling and is more than 1.5 times its height from a building
containing sleeping accommodation


Temporary build
ings
:
Buildings erected for less than 28 days


Ancillary buildings
:
Buildings used in connection with the sale of buildings or plots on that site,
or in connection with a building project or mine/quarry and contains no sleeping accommodation.


Small detach
ed buildings (garages, workshops or sheds)
:
A detached single storey building
with less than 30m
2
internal floor area, with no sleeping accommodation. If constructed
substantially of combustible materials it must be positioned at least one metre from the b
oundary
of its
curtilage
.

Other detached buildings with less than 15m
2
internal floor area, with no sleeping
accommodation. (no boundary restrictions if constructed of combustible materials)


Conservatory, porch, covered yard/way & carports:
A detached si
ngle storey building with
less than 30m
2
internal floor area, fitted with safety glass in critical locations in compliance with
ADN.
Existing walls, doors & windows of the building separating the conservatory or porch is to
be retained or, if removed are

replaced with elements that meet the energy efficiency
requirements of ADL1B. The heating system of the dwelling must not be extended into the
conservatory or porch. Carports must be open on two sides
.


4.0 Competent Person Scheme

Certain works can be car
ried out by an installer who is registered with a Competent

Persons Scheme and will not require building regulations approval.
For a list of all

scheme members go to
www.competentperson.co.uk


5.0 Planning Permission, listed building & conservation area
consents

Planning permission, listed building/conservation area consents may be required for your

proposed development and no works should be commenced until approval has been

given by the planning department.


If the requirements of the building regula
tions will unacceptably alter the character or

appearance of a historic/listed building/ancient monument or building within

a conservation area, then the requirements may be exempt or improved to what is

reasonably practical or acceptable and would not
increase the risk of deterioration of the

building fabric or fittings in consultation with the local planning authorities conservation

officer. For any further information, p
lease contact the FODDC duty planning officer on

01594 810000.







Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


10

6.0
The Pa
rty Wall Act 1996

The Party Wall Act 1996 came into effect on 1 July 1997 to provide guidelines for preventing or

resolving disputes between neighbours regarding their party walls. If you intend to carry out work

that affects a wall between you and your
neighbour, for example:

1.

Work to an existing wall or structure shared with another property including:

a.

support of a beam,

b.

insert dpc through wall,

c.

raise wall or cut off projections,

d.

demolition and/ or rebuilding,

e.

underpinning
,

or

f.

inserting a lead flas
hing etc

2.

Building a free standing wall or a wall of a building that is up to or astride your boundary

3.

Excavating within 3 meters of an existing structure where the new foundations will go
deeper than the adjoining foundations, or within 6 meters of an ex
isting structure where
the new foundations are within a 45 degree line of the adjoining foundations,

then you must find out if the Party Wall Act is relevant in your case. If the work you carry out is

covered by the Act, then you must follow the relevant
procedures to inform your neighbours that

such work is to take place.


Informing your neighbours
:
If the work you are undertaking is covered by the Act, then you

must inform your neighbours with at least the following information:



Your name and address



The buildings address if different from your own



A clear statement that your notice of intention to undertake the work is under the

provisions of the Party Wall Act.



Full details of your proposal



When you propose to start the work

You must serve the not
ice at least two months before you start the work on party walls or one

month for party fence walls of excavations that are close to your neighbours walls. The notice is

only valid for one year.


After the notice is served
:
Once you have served a notice

on your neighbour they can:



Give written consent within 14 days for the work to take place



Serve a counter notice requiring additional work to be carried out



Object to the work being done. If after 14 days your neighbour has not replied to


your notice
, a dispute is deemed to have arisen.

If you receive a counter notice requiring extra work to be carried out, you must respond to it

within 14 days. If you fail to respond to this counter notice a dispute will be regarded as having

arisen.


Resolving dis
putes
:
If either you or your neighbour have objected to the others notice and the

dispute cannot be settled by way of a friendly discussion, then the problem should be resolved by

the appointment of surveyor. A surveyor may be appointed by both parties o
r each party may

appoint their own surveyor. The surveyor or surveyors will draw up a document which will

include:



A description of the work that is to be carried out



When and how the work is to be carried out



A description of the condition of the neig
hbour's property prior to the work commencing



Conditions allowing the surveyor(s) access to inspect the work as it is carried out

The surveyor will decide who pays the fee for drawing up the document, although it is usual for

the person undertaking the w
ork to pay all costs.


Conclusion
:
As most buildings or building work will be close enough to the neighbour's property

to be covered by the Act, it is essential that all those involved in the construction process

understand the purpose and effects of the

Act.

For further information and an explanatory booklet

on The Party Wall Act is available free of charge from:
www.communities.gov.uk


Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


11

7.0
Rights of Light

Introduction
:
Rights of Light are rights that can be enjoyed by a building. Put simply it is a r
ight

of a building to enjoy light coming in over someone else‘s land. If Rights of Light are in place

they are protected by law, and court action can be brought against someone who has ―injured‖

them or, quite importantly, someone who intends to injure

them. The right is limited, but the

courts are severe where a right is proved to be ―injured‖.

The general principles on which the courts rely are those, established over many years,

summarised below. These general items are not an entire list of all p
rinciples involved, and the

descriptions given are not legal definitions. Expert advice is usually needed not only on the

principles applying to any particular situation, but also for the detailed calculations needed to

establish if an ―injury‖ can be
proved. Legal advice is usually necessary relating to provisions

within Deeds and Covenants:


Does a Right of Light exist?

A room within a building may enjoy a right of light, but it may not

necessarily do so as explained below. Unless granted by a Dee
d, an Implied Grant, or some

other agreement, a right of light normally has to be gained. It would be unusual for a right to be

in place as soon as a building is constructed.

The law sets a period of twenty years for a room to gain a right of light th
rough its window(s).

However, the ability to gain a right can be prevented, for all time by restrictive wording in the

Deeds, or temporarily by obstruction during the twenty year period, or other legal means. For

example much former Coal Board land, o
r Forestry Commission land, prevents rights of light ever

being gained. Expert or Legal advice should be sought on these matters.

A room cannot gain a

right to a view or a right to sunlight. Also, open spaces such as garden areas cannot have Rights

of

Light.


What is a Right of Light?

Where a right of light exists the building has a beneficial advantage,

legally an Easement, over the adjoining property. The building has a right to the light entering its

windows across that adjoining property. It is
fundamental that there must be a dominant and a

servient tenement (two properties) and that the owners must be different persons. The property

enjoying the right of light is the dominant tenement.

Even with an established right of light there is nothing

to prohibit the amount of light entering its

windows into a room being reduced, so long as a certain minimal standard remains within that

room. If the adjoining owner (the servient tenement) does something so as to interfere with the

amount of light t
o the extent that the minimal standard is transgressed, an ―injury‖ results which is

actionable at law. Further, the right to light is a property right and so action can be taken in

advance of a transgression happening, so as to prevent the injury.


So
what is an Injury?

It has been determined in the courts that the minimum amount of natural

light on a working plane in a room should be one lumen. That is a fairly low lighting level, but it is

based on the eye being able to cope with a reasonable discr
imination of detail. The lighting level

is equivalent to one candle held one foot away from a surface, with no other light input. Even

then there is a ―working rule‖, accepted by very many legal precedents, that however much area

of a room originally h
ad one lumen or more, and ―injury‖ would only be proved if the room in

question were to be left with less than about half its area (50/50) receiving one lumen.

The working rule of 50/50 is used to determine if an injury has occurred. Further if Damages


(rather than an Injunction: see later) becomes the issue at law, the amount by which the 50/50

area is transgressed can be used to calculate financial loss in a structured and equitable manner.

This technique applies a ―value‖ for the right of light a
s a proportion of rental, but for any

capitalisation calculations specialist advice will be needed.

Where domestic properties are concerned the ―working rule‖ of 50/50 has been slightly modified,

and it has been shown that up to 55% of the working plane
should remain ―well lit‖ by natural light

to the one lumen standard. If less than 50% an injury would most certainly be proved, but if 50



55% remains well lit the injury is not so clear cut. Over 55% remaining well lit (again to the one
lumen standar
d) shows no injury.


How do you establish if there is an Injury?

The method of establishing if an injury has

occurred is to perform calculations to create a line, drawn on the plan of the room, where just one

lumen of natural light is received on the wor
king plane (850 mm above floor level).

To do this the Expert knows that the whole hemisphere of the sky provides 500 lumens

Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


12

(accepted by the courts as being equivalent to an overcast winter). For the on lumen level

therefore, a point on the working pl
ane must receive just one five hundredth of that amount. Put

another way a point on the working plane must be able to ―see‖ just 0.2% of the sky, that is quite

a small amount.

The calculations are normally undertaken by an Expert using Waldram Diagrams
or computer

modelling to consider various points in the room. These techniques map the window(s), and the

obstructions outside, onto a grid of the sky so as to correct for curvature. Examining the results

allows a line to be drawn on the plan of the r
oom, at working plane level, showing the limits of

where the one lumen requirement is achieved. The Expert then calculates what percentage of

the room area receives one lumen or more, and what does not. If a new obstruction, such as a

tall building prop
osed near a room‘s windows, reduces the amount of light to below the minimal

standard (the 50/50 or 55/45 rule) only then can an ―injury‖ be proved in court.


What happens where there is an Injury?

A right of light is protected by law and if the owner of

a servient tenement injures a dominant tenement in the way described, an Injunction may be

obtained through the courts. This means the building work can be prevented or, if it is underway,

stopped. Even more dramatic is the likely hood that the offend
ing part of a new building has to

be knocked down.

The courts may hold, only in a minority of circumstances, that Damages are

more appropriate than an Injunction. The award of Damages does allow the ―offending‖

development to remain (or to proceed), bu
t awards compensation. However for Damages to be

the outcome, the legal precedent set in Shelfer v City of London Electric Lighting Company: 1895

must be observed. The more likely outcome if an injury is proved, is for an Injunction to prevent,

or rem
ove, the new structure.


Reference Sources
:
For further information and interpretation of all the above Expert and

probably Legal advice is required. ―Anstey‘s Rights of Light‖ which is published by the Royal

Institution of Chartered Surveyors (RICS Book
s ISBN 9781842192221).


8
.0 Construction (Design and Management) Regulations 2007 (CDM)

The Construction (Design and Management) Regulations 2007 apply to every

construction project. If you are about to undertake construction work, which could include

alterations, extensions, routine maintenance, new build or demolitions, then you need to

know to what extent these Regulations will apply to you and whether you are a duty

holder under these Regulations.


With non
-
domestic* projects expected to last lon
ger than 30 days, or more than 500 man

hours, you will require the assistance of an advisor called a CDM Co
-
ordinator, who

should be appointed at the earliest opportunity, before detailed design work is complete.


If you are a Client thinking of commissi
oning work, a Designer appointed to work on a project, or

a builder/developer about to undertake work, you should be aware of your responsibilities or

duties under CDM 2007.

*Non
-
domestic Clients are people who commission building works

related to a tra
de or business, whether for profit or not. This work can be carried out on a

domestic property; it is the type of Client that matters, not the type of property.


9
.0 Protection of Bats

For all works including demolition, conversions, extensions and or alt
erations that would involve
changes to the roof
-
space, please note that
all bat species are protected under schedule 5 of the
Wildlife & Countryside Act 1981, and also under Schedule 2 of the Conservation of Habitats &
Species Regulations 2010. It is an o
ffence to: intentionally or recklessly kill, injure or capture
(take) bats; intentionally or recklessly disturb bats (whether in a roost or not); or damage, destroy
or obstruct access to bat roosts. If you think that bats may be using
the
property or you
discover
a bat whilst development work is being undertaken, stop the work immediately and contact the
National

Bat Helpline on 0845 1300 228.




Building
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ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


13

10
.0 Preliminaries

for p
reparation, protection, access and demolition

Demolitions,
existing structures to be suppo
rted & protected where necessary

& new openings
formed

to structural engineers design

& structural calculations where necessary
,
any existing sub
structures (e.g.
foundations and slab etc
)
,
taken up & removed off site to a licensed tipping site.

Where the
demolition of a structure or part of a structure exceeds 50m3
,

a notice of the proposed
demolition should be sent to
the local authorities
building control

department

before works
commence.

Standard format notice is available to down load at our web site:
www.fdean.gov.uk
.


Provide all necessary
health and safety requirements including;
site security, scaffolding, access
ladders, material hoists, temporary protection and working platforms etc which are to be erected
,
maintained, certificated, dismantled and removed by suitably qualified and insured specialists.


All plumbing, drainage, heating, electrical services etc including re
-
siting of heating
appliances/boilers/flues etc to be altered/modified/adjusted as nece
ssary by suitably qualified &
experience specialists or registered competent persons, tested & appropriate certification issued
where required in this specification.


Any asbestos/contaminated soil
/lead paint

is
to be inspected & removed by a specialist.

Asbestos
is to be

removed and disposed off site by a specialist licensed contractor

as required under the
Control of Asbestos Regulations 2006
.


Ground to be prepared for new works as described including location and alteration/

modifications to all exis
ting services as necessary, including sealing up, capping off,
disconnecting, removing redundant services as necessary. Prior to and during works, the person
carrying out the works is to liaise with and meet the requirements of the relevant Service
Authori
ties, including the location and protection of all services as necessary.


External paths, drives, patios, walls, fences & gardens etc, to be taken up and relayed/

extended
as necessary to accommodate the new works as described.


All structural timber
is to be grade C24, stress graded to BS 4978 and sawn to BS 4471. All
timber is to be protected on site to minimize moisture content which must not exceed 22%.


Builder to allow for opening up existing structure where required for inspection purposes in
a
reas/locations as requested and making good all disturbed structures and finishes to match
existing.























Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


14

1
1
. Technical & practical guidance for
domestic extensions


Part A: Structure


A1: Sub structure



Foundations (including retaining
walls & basements)

Foundations

to be in accordance with Approved Document A1/2,

and
constructed at a minimum
depth of 750
-
1000mm, below the influence of drains, and or surrounding trees
,

on level firm
natural undisturbed ground of adequate ground bearing
capacity to the approval of the building
control surveyor.


Strip foundations

Strip foundations to
have
a minimum width of 600mm and thickness of 2
00
mm
.

The concrete mix
should be ST2 or GEN1.


Diagram 1:
Strip

foundation
section
detail

(not to scale)



Trench fill foundations

Trench fill foundations should have a minimum width of 450mm and a minimum 500mm
thickness of concrete. The concrete mix should be ST2 or GEN1.



Diagram
2
:
Trench fill
foundation
section
detail

(not to scale)






600 wide x 200mm thick concrete strip foundation
to be 750-1000mm deep depending on sub soil
conditions. Actual sizes and depth to be agreed
on site with building control surveyor. Foundation
depths in relation to trees to be in accordance
with NHBC tables- contact building control for
guidance.
600mm
Ground level
Cavity wall as guidance details
450-500 wide x 500-750mm thick trench fill
concrete foundation to be 750-1000mm deep
from ground depending on sub soil conditions.
Actual sizes and depth to be agreed on site
with building control surveyor. Foundation
depths in relation to trees to be in accordance
with NHBC tables- contact building control for
guidance.
450-500 mm
Ground level
Cavity wall as guidance details
Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


15

Alternative

fou
ndation designs

Alternative foundation designs, i.e. raft, piles, retaining walls & basement to be designed by a

suitably qualified person and approved by building control before works commence on site.

Where applicable, a suitable basement tanking syste
m is to be assessed & designed by a

tanking specialist suitable for the site conditions & proposed building construction to prevent the

passage of moisture into the building, which must be approved by building control before works

commence. Retaining wa
lls require 100mm diameter slotted ground water drainage pipe laid

around the outside base perimeter of any retaining wall at 1:60 gradient and taken to a suitable

sized soak away system.



Sub structure

Foundations are to be provided centrally positi
oned under all exterior, party and interior load
bearing walls, steps in foundation level should not exceed its thickness and should overlap by
twice its thickness

as detailed in the diagram below
. Two layers of
B
503 mesh reinforcement or
stronger are to
be provided, one top and bottom with 75mm cover to the foundations in the Forest
of Dean mining and Mineral Valuer areas (please contact building control for area details).


Walls below DPC level up to 1m deep are to be constructed with two skins of 7N/mm²

100mm or
140mm if over 1m deep concrete blocks 1:3 cement mortar in
-
filled with concrete to a maximum
of 225mm below DPC level. Block and cavity width and wall tie spacing, etc, to be same as the
wall above, but with a row of wall ties to support the cavi
ty wall insulation below DPC level.

All
materials to be frost resistant.



Diagram 3
: Stepped foundation
section
detail

(not to scale)


















Foundations should unite
at each change in level
L
S
T
S should not be greater than T
(for trench fill foundations, minimum
overlap L = twice height of step or
1metre, whichever is the greater)
Minimum overlap L = twice height
of step, or thickness of foundation
or 300mm, whichever is the
greater
Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


16

Ground bearing solid concrete floor
s

Suitable for basic radon protection only

(U
-
value 0.22 W/m².k)



T
opsoil and vegetable matter to be cleared from site and floor to be in filled
between walls
with
minimum 150mm/maximum 600mm clean sand blinded compacted hardcore.


1200g (300 micrometer)
continuous polythene D
amp proof membrane (DPM) and
radon
gas
proof
barrier is to

be

laid
over
sand
blinded hardcore
, lapped & sealed at all joints

&

linked to
DPC‘s in walls.
To provide basic protection from radon

gas
, the damp
-
proof course within
the

cavity wall should be in the form of a cavity tray
& sealed to DPM
to p
revent radon from entering
the building through the cavity. Sealing of joints in the barrier and sealing around service
penetrations are also required

with radon gas proof tape

in compliance with part C of this
guidance
.


F
loor grade insulation

to be laid

over DPM, minimum

thickness and type in
accordance with
t
able
below

including

25mm thick insulated up
-
stands between slab and external walls.


1
00mm
minimum
thick ST2, or Gen1 concrete floor slab with a t
r
owel

smooth surface

ready for
finishes

to be laid
over insulation, (note:
500g polythene separating layer
is
to be installed
between the

concrete slab and insulation if using a foil faced polyurethane/

PIR type insulation
board.
)

Insulation to be omitted and concrete thickness increased in areas where non
-
load
bearing partitions are built off the floor slab. Where area of fill exceeds 600mm the floor is to
be
suspended as detailed in this guidance.



Diagram
4
: Typical section through a ground bearing solid concrete floor

& foundation
.

S
uitable for
basic

radon protection

only

(not to scale)






65mm thick bonded cement/sand
screed (optional)
100mm minimum thick concrete slab
Separarating layer if required beween
slab & insulation - see guidance for
details
Floor grade insulation (see options in
guidance table)
1200g damp proof membrane/radon
gas barrier*
Sand blinded hardcore mechanically
compacted in 150mm layers. (floor
slab to be suspended where depth of
fill exceeds 600mm deep)
600mm
All external widows and doors to be double
glazed (see options in guidance table)
100mm minimum width insulation block (see
options in guidance table)
Wall grade insulation (see options in guidance
table)
50mm clear cavity if using partial fill cavity wall
insulation (see options in guidance table)
Stainless steel wall ties and spacings as detailed
in guidance
100mm minimum width external wall in
materials to match existing or as specified in
planning permission
25mm wide insulation to prevent cold
bridging
radon dpc tray sealed
with gas proof tape to
dpm/radon barrier*
Back fill cavity with
concrete
600 x 200mm concrete strip foundation or
trench fill foundation as detailed in specification,
to be 750-1000mm deep depending on sub soil
conditions. Actual sizes and depth to be agreed
on site with building control surveyor. Foundation
depths in relation to trees to be in accordance
with NHBC tables- contact building control for
guidance.
*Note: Ground supported floor slabs are only suitable for basic radon
protection- see other options in guidance for full radon protection.
Damp proof course
and insulated closer
DPC 150mm above
ground level
Weep holes
Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


17

Suspended reinforced in
-
situ concrete ground floor slab supported on internal walls
.
Suitable for basic & full radon protection

Topsoil and vegetable matter to be cleared from site and floor to be in filled bet
ween walls with
minimum 150mm/maximum 600mm clean sand blinded compacted
hardcore.

Where full radon protection is required, a sub floor sump, depressurization pipe with up stand is
to be positioned below the over site concrete floor slab in radon gas perme
able hardcore
-
in
accordance with sump manufacturers details and part C of this guidance.


Shutter
and cast

reinforced
concrete floor slab
supported on inner leaf of the cavity
wall in
accordance with structural engineers details and calculations to preve
nt settlement of the slab
and rupture of the radon
-
proof barrier.
1200g (300 micrometer) continuous polythene
d
amp proof
membrane (DPM)
/
radon gas proof barrier is to be laid over
concrete slab surface,
lapped &
sealed at all joints & linked to DPC‘s in wal
ls. To provide basic protection from radon gas, the
damp
-
proof course within the cavity wall should be in the form of a cavity tray & sealed to DPM to
prevent radon from entering the building through the cavity. Sealing of joints in the barrier and
sealing

around service penetrations are also required with radon gas proof tape
.


Floor grade insulation to be laid over DPM, minimum thickness and type in accordance with table
below including 25mm thick insulated up
-
stands between slab and external walls.

75mm
minimum thickness sand/cement screed
be laid over insulation

with a trowel smooth surface
ready for finishes.

(note: 500g polythene separating layer is to be installed between the
screed

and insulation if using a foil faced polyurethane/ PIR type insulatio
n board.) Insulation to be
omitted in areas where non
-
load bearing partitions are built off the floor slab.


Diagram
5
: Typical section through a
suspended reinforced in
-
situ c
oncrete
ground
floor
slab
supported on internal walls.
Suitable for basic & ful
l radon protection
(not to scale)








75mm thick bonded cement/sand screed
500g separating layer between foil
backed insulation & screed if required
Floor grade insulation (see options in
guidance table)Insulation can also be
positioned below slab with separating
layer between concrete & insulation as
above
1200g damp proof membrane/radon gas
barrier
Suspended steel reinforced concrete slab,
shuttered and supported on inner leaf of
cavity wall- sizes of steel mesh, slab
thickness and minimum bearing to be
designed suitable for clear spans and
loadings in accordance with structural
engineers details & calculations
Radon gas sump and depressurisation
pipe for full radon gas protection must be
installed below the concrete slab &
upstand extended above ground level
with cap & radon pipe signage ready for
connection of future radon gas fan & flue
if required
600mm
Insulated cavity wall construction
as guidance details
radon dpc cavity tray
sealed with gas proof
tape to dpm/radon
barrier
Sand blinded gas permeable hardcore
mechanically compacted in 150mm layers.
600 x 200mm concrete strip foundation or
trench fill foundation as detailed in guidance,
to be 750-1000mm deep depending on sub soil
conditions. Actual sizes and depth to be agreed
on site with building control surveyor. Foundation
depths in relation to trees to be in accordance
with NHBC tables- contact building control for
guidance.
DPC 150mm above
ground level
Back fill cavity with
concrete upto radon/
dpc cavity tray level
Weep holes
Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


18

Suspended beam & block ground floor
s

Suitable for basic & full radon protection

(U
-
value 0.22 W/m².k)
.
Remove top soil & vegetation, apply total weed killer


minimum space
below underside of floor to be 150mm. PC
C beams to be supplied and fixed to

beam
manufacturers plan layouts
and details. (copies to be sent to Building Control and approved
before works commence on site).


Typically for domestic loading and spans pre
-
stressed beams are 155mm deep X 125mm wide
an
d fixed at 520mm
centers
, minimum bearing 100mm onto DPC course and load bearing walls.
All garage floors to be designed suitable for loadings.


W
et and grout all joints with 1:4
cement/sand mix.

Below non
-
load bearing parallel partitions provide double be
ams.

Sub structure
void to be vented on opposing sides to provide cross ventilation using 225 X 150mm proprietary
ventilators at 2
.0m centers
,
sub floor
level to be above external ground levels.



1200g (300 micrometer) continuous polythene Damp proof memb
rane (DPM) and radon gas
proof barrier is to be laid over beam and block floor, lapped & sealed at all joints & linked to
DPC‘s in walls. To provide
basic r
adon gas

protection
, the damp
-
proof course within the cavity
wall should be in the form of a cavity
tray
& sealed to
the DPM
to prevent radon

gas

from
entering the building through the cavity. Sealing of joints in the barrier and sealing around service
penetrations are also required with radon gas proof tape.
Where full radon protection is required,
prov
ision is to be made for connection of future depressurization pipe to vented floor & up stand
in accordance with
manufactures details
.

Floor grade insulation to be laid over DPM, minimum thickness and type

of insulation to be

in
accordance with table bel
ow including 25mm thick insulated up
-
stands between screed and
external walls.

75mm sand/cement structural screed to be laid over insulation

with trowel smooth
finish ready for finishes
, (note: 500g polythene separating layer is to be installed between the

concrete slab and insulation if using a foil faced polyurethane/PIR type insulation board.)
Insulation to be omitted where non
-
load bearing partitions are built off the beams to beam
manufacturers design details.


Diagram
6
: Typical section through a sus
pended beam & block ground floor

(not to scale)

Suitable for
basic &
full radon protection




600mm
Alternative postion for
1200g radon gas barrier
over complete foot print of
building and no more than
225mm below ground level
600 x 750mm (adjusted to foundation depth)concrete trench
fill foundation as detailed in specification, to be 750-1000mm
deep depending on sub soil conditions. Actual depth to be
agreed on site with building control surveyor. Foundation
depths in relation to trees to be in accordance with NHBC
tables- contact building control for guidance.
Damp proof course & insulated
closer
Weep holes
225 x 75mm grilled air bricks
& proprietary telescopic vents
through opposing walls at
2.0m ctrs*
DPC 150mm min above gl
Double glazed windows as detailed in specification
Cavity wall construction as detailed in specification
Continuous dpc tray sealed with gas proof tape to dpm
75mm sand/cement screed
Floor grade insulation (see options in guidance table)
1200g dpm/radon barried
Pcc beam suitable for spans & loadings
as beam manufacterers details

100mm dense conc blocks
75mm min
air void
*Note: for full radon protection a radon gas fan & flue should be connected to
the floor vents if required
dpc under beams
75mm concrete blinding layers to protect
alternative radon gas barrier position
225mm max
to radon barrier
Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


19

Table 1: Ground bearing slab & suspended beam & block ground floor insulation
requirements.
U
-
value no worse than 0.22 W/m²k

NOTE:
Where P/A ratio has not been c
alculated use insulation thickness stated in 1.0*

Required thickness of insulation (mm)

Insulation
product

K
-
value

Calculated
Perimeter/Area ratio

(P/A)

1.0
*

0.9 0.8


0.7 0.6 0.5 0.4 0.3 0.2 0.1

Kingspan

Kooltherm K3

0.021

75

70

70

70

70

70

60

60

50

20

Celotex

GA4000

0.022

75

75

75

75

70

70

65

60

50

20

Knauf Polyfoam

Standard
floorboar
d

0.029

100

100

100

100

85

85

75

75

50

50

Jablite Jabfloor

Premium

0.030

100

100

90

90

85

80

75

65

50

30

Styrofoam

Fl
oormate 300A

0.035

100

100

100

100

90

90

90

80

60

50

Rockwool

Rockfloor

0.038

135

130

130

130

125

120

115

100

80

30

Note 1. Figures indicated above should be adjusted to the insulation manufacturers nearest

thickness

Note 2
*
. Where P/A ratio has not bee
n calculated use insulation thickness stated in 1.0
*

above

Note 3. Insulation to be installed in accordance with manufactures details


Floating floor

Alternatively instead of cement/sand floor screed, a floating timber board floor can be laid over
the in
sulation using 22mm
minimum
thick moisture resistant tongue and grooved timber floor
board sheets with all joints glued and pinned, in compliance with floor board manufacturers
details and current BS EN standards. Minimum thickness and type of insulation t
o be in
accordance with the table below
.


Table 2: Floating floor insulation requirements.
U
-
value no worse than 0.22 W/m²k

NOTE:
Where P/A ratio has not been calculated use insulation thickness stated in 1.0*

Required thickness of insulation (mm)

Insu
lation product

K
-
value

Calculated Perimeter/Area ratio (P/A)


1.0
*

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2

Kingspan Kooltherm K3


0.021

100

95

95

90

85

80

70

60

40

Kingspan Thermafloor

TF70 & Celotex
GA4000


0.02
3

105

100

100

95

90

85

75

65

40

Note 1. Figures indicated above should be adjusted to the insulation manufacturers nearest

thickness

Note 2
*

Where P/A ratio has not been calculated use insulation thickness stated in 1.0
*

above

Note 3. Insulation to be i
nstalled in accordance with manufactures details












Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


20

Suspended timber ground floor

Suitable for basic & full radon protection

(U
-
value 0.22 W/m².k)

Remove top soil & vegetation, apply total weed killer & 150mm min thick sand blinded hardcore,
lay 1
00mm min thick reinforced concrete over

site (concrete mix should be in accordance with BS
8110, BS 5328, mix type ST2 or GEN1), on
1200g (300 micrometer) damp proof membrane
(DPM)/radon gas proof membrane
which should extend across
foot print of building
and

cavity
wall
for

basic
r
adon
gas
protection
. Radon barrier should be no more than 225mm below external
ground level

and positioned to prevent water collection.

Where full radon protection is required, a
sub floor sump, depressurization pipe with up stan
d is to be positioned below the over site
concrete floor slab in radon gas permeable hardcore
-
in accordance with sump manufacturers
details and part C of this guidance.


Allow a ventilated air space at least 75mm from the top of the over

site concrete to
the underside
of any wall plates and at least 150mm to the underside of the suspended timber floor or
insulation. Provide sub floor ventilation using 225 x 75mm grilled air bricks & proprietary
telescopic vents through two opposing external walls at 2.0m
c
enters

to vent all parts of the floor
void.


Joists to be supported off proprietary heavy duty
galvanized

joist hangers. Hangers to be built
into new masonry walls or fixed to treated timber wall plate (same size as joists), resin bolted to
existing walls

at 600mm
centers

using 16mm diam
eter

high tensile bolts. Where necessary, floor
joists can be supported on treated wall plates &
damp proof course (DPC)

onto masonry
honeycombed sleeper walls
built off
over

site concrete.

Floor joists sizes as stated on p
lans, or
t
able below. Joists to be grade C24 kiln dried floor joists fixed at 400mm
centers
(depth to be
increased where necessary to match floor levels). Proprietary galvanized steel strutting to be
fixed at mid span for 2.5
-

4.5m span and 2 rows at 1/3r
d points for spans over 4.5m.


Floor to be insulated with floor grade insulation thickness and type in

t
able below, friction fixed
between joists. Fix
22mm thick moisture resistant tongue and grooved timber floor boards deck
sheets with all joints glued an
d pinned, in compliance with current BS EN standards

laid with long
edge across the joists. All joints to positioned over joists, glued & nailed using 55mm X 10g
annular ring shank nails.


Diagram
7
: Typical section through a suspended timber ground floor
(not to scale)

Suitable for basic
radon protection
(& full radon protection if
radon
sump
is
provided below slab)


225mm max
to radon barrier
600mm
Double glazed windows as guidance table
Insulated cavity wall construction as guidance details
22mm moisture resistant t & g flooring sheets
Floor joists (see options in guidance table)
Galv hangers built into walls or fixed to wall plates resin
bolted to walls
Insulation fixed between joists & supported on battens
fixed to joists (see insulation options in guidance table)
w/plate on dpc
honey combe sleeper wall 75mm
min
100mm oversite concrete slab
Blinded hardcore
600 x 750mm (adjusted to foundation depth)concrete trench
fill foundation as detailed in specification, to be 750-1000mm
deep depending on sub soil conditions. Actual depth to be
agreed on site with building control surveyor. Foundation
depths in relation to trees to be in accordance with NHBC
tables- contact building control for guidance.
Damp proof course & insulated
closer
Weep holes
Dpc tray
225 x 75mm grilled air bricks
& proprietary telescopic vents
through opposing walls at
2.0m ctrs
DPC 150mm min above gl
150mm
min
*Note: for full radon protection a radon gas sump and depressurisation pipe must be
installed below the oversite concrete slab & upstand extended above ground level with
cap & radon pipe signage ready for connection of future radon gas fan & flue if required
dpc
1200g basic radon gas
barrier over complete foot
print of building and no
more than 225mm below
ground level
Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


21

Table
3
:
Suspended timber ground floor

insulation requirements
.

U
-
value no worse than 0.22 W/m²k

Required thickness of insulation (mm)

Ins
ulation product

K
-
value

Calculated Perimeter/Area ratio (P/A)


1.0
*

0.9 0.8 0.7 0.6 0.5 0.4


0.3 0.2

Kingspan TF70


0.023

110

110

110

110

110

100

100

90

70

Celotex FR4000


0.022

110

110

110

110

110

100

100

90

70

Jablite Jabfloor

Premium 70

0.030

130

130

125

125

120

110

100

85

60

Jablite Jabfloor 70


0.038

160

150

150

145

140

130

120

105

70

Rockwool Flexi


0.038

140

140

140

140

140

140

140

120

90

Knauf Earthwool loft roll
40

& loft roll 44


0.040

0.044

2
00

200

200

200

200

170

150

150

150

Note 1. Figures indicated above should be adjusted to the insulation manufacturers nearest
thickness

Note 2
*
. Where P/A ratio has not been calculated use insulation thickness stated in 1.0
*

above

Note 3. Insulation to b
e installed in accordance with manufactures details


Garage
ground bearing
concrete floor

Power floated 150 mm thick concrete slab (concrete mix should be in accordance with BS 8110,
BS 5328, mix type ST2 or GEN1), with 1 layer A252 steel mesh positioned

mid span of slab on
1200g
polythene damp proof course/
radon barrier on sand blinding on min. 150 well consolidated
sulphate free clean hardcore.(no reclaimed demolished material is permitted).


1:80 fall on floor from back of garage to front garage door,
floor to be thickened to 300mm at
garage entrance.


Provide 25mm polystyrene compressible clay

board to perimeter of walls.

If hardcore is more than 600mm deep
-

slab to be reinforced further, to NHBC/LA/Engineers
requirements.


100mm thick masonry
step

do
wn into garage to be provided at doorways.


Radon
gas
protection to be
provided in garages integral with the dwelling in accordance with the
above ground bearing/suspended floor details

















Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


22

Diagram
8
: Typical section through a
ground bearing ga
rage
floor & foundation (not to
scale)





































150mm thick concrete slab
1 layer A 252 steel mesh mid span
1200g damp proof membrane
Slab thickened at doorway
600mm
DPC
600 x 225mm concrete
strip foundation or
trench fill foundation as
detailed in specification,
750-1000mm deep as
agreed on site with
building control surveyor
Sand blinded hardcore
mechanically compacted in
150mm layers. (floor slab to be
suspended where depth of fill
exceeds 600mm deep)
Painted render on 100mm dense
conc block or bricks
Piers built off fnds & extend full
height of walls & gables
Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


23

A2: Superstructure


External walls


Cavity walls
(U
-
value not worse than 0.28 W/m².k)

External wall constructed in either 100mm thick reconstituted stone facings,100mm thick 5N/mm²

(min) facing brickwork or 2 coat render on 100mm thick dense concrete block skin (in materials
and finishes to match existing where necessary and dependent upon exposure) with a 100mm
(min) thick 2.8N/mm² (min) insulation/dense block inner leaf with eithe
r a 15mm lightweight
plaster finish or 12.5mm plasterboard on dabs skimmed dry lining as table below. Where
required, 100
-
150mm thick matching external natural stone facings to be tied to 100mm thick
dense concrete block backing course (or British Board of

Agreement (BBA) approved proprietary
cavity spacer system and omit concrete block), connected together with wall ties as detailed
below and foundation widths increased by 150mm.


Walls to be built with 1:5/6 cement mortar and tied with BBA approved stain
less steel wall ties
suitable for cavity width at maximum spacing of 750mm horizontal (increased to 600mm if
retaining partial fill insulation using proprietary retaining rings as manufacturers details), 450mm
vertical and 225mm at reveals, verges and clos
ings for cavities up to 100mm wide. Wall ties and
spacing for cavities over 100mm wide to be in accordance with wall tie manufactures details.


Cavity width and insulation details to be constructed as table below to achieve a U
-

value not
worse than 0.28
W/m².k. Wall insulation to be continuous with roof insulation level and taken
below floor insulation levels as manufacturer‘s details.


Sizes of structural elements, thickness of walls, height and size of buildings to be in accordance
with ADA 1/2. Openin
gs, buttressing and sizes of openings and recesses to be in accordance
with diagrams 13, 14 and 15 of ADA1/2. Openings exceeding 2.1m in height or openings less
than 665mm measured horizontally to an external corner wall should be in accordance with
detail
s and calculations from a suitably qualified person




Table 4: Partial cavity fill
i
nsulation requirements for external cavity walls
100mm dense
brick or rendered block external skin & 15mm internal lightweight plaster/plasterboard on dabs
finish. U
-
value

no worse than 0.28 W/m²k

Clear cavity

width required

Insulation type &

Minimum thickness

Overall cavity

width required

Internal Block Type

& Thickness

50mm
1

40 mm Kingspan

Kooltherm K8 or

Other approved with

K value of 0.020

90mm
1

100 mm insulation blo
ck
-


K value 0.15 or lower

(Celcon Standard)

50mm
1

40mm Celotex

CG4000 or other

approved with K value

of 0.022

90mm
1

100 mm insulation block
-


K value 0.11 or lower

(Celcon Solar or

Thermalite Turbo)

50mm
1

50 mm Kingspan

Kooltherm K8 or

Other appro
ved with

K value of 0.020

100mm
1

100 mm dense concrete

block (K value 1.13)


50mm
1

60mm Celotex

CG4000 or other

approved with K value

of 0.022

110mm
1

100 mm dense concrete

block (K value 1.13)


Notes: 1. Clear cavities can be reduced to 25mm in c
ompliance with certain insulation

manufacturers details
-

subject to any building warranty providers approval where

applicable



Building
c
ontrol guidance for
DOMESTIC
EXTENSIONS
:

May 2011


24

Table 4
.1
:
Full

cavity fill
i
nsulation requirements for external cavity walls
100mm dense
brick or rendered block extern
al skin & 15mm internal lightweight plaster/plasterboard on dabs
finish. U
-
value no worse than 0.28 W/m²k


Clear cavity

width required

Insulation type &

Minimum thickness

Overall cavity

width required

Internal Block Type

& Thickness

n/a

100mm Dritherm 37

or other approved

with K value of 0.037

100mm

100 mm insulation block
-


K value 0.11 or lower

(Celcon Solar or

Thermalite Turbo)

n/a

100mm Dritherm 34

or other approved
with K value of
0.034

100mm

100 mm dense concrete

block (K value 1.13)

n/a

85mm
Dritherm 32

or other approved

with K value of 0.022

85mm

100 mm insulation block
-


K value 0.16 or lower

(Topblock Toplite

Standard)

Notes: 1. Clear cavities can be reduced to 25mm in compliance with certain insulation

manufacturers details
-

su
bject to any building warranty providers approval where

applicable



Walls between heated and un heated areas

(
U
-
value

0.28 W/m².k)

Walls between heated and

unheated
areas

such as garages etc, to be constructed and insulated
as external walls or construct
ed
with

2.8/mm² 100
/215
mm solid dense concrete blocks with
light
weight plaster/plaster board on dabs finish to one side,
50 X 75mm deep timber studs or
proprietary metal stud partition wall system

to the opposite side,

with insulation friction fixed
betwe
en vertical studs (as detailed in table below),finished with 12.5mm vapour checked plaster
board (or 500g polythene vapour check) a
nd 3mm skim

coat plaster


Table
5
: Insulation requirements to
solid walls between heated & un heated areas

U
-
value no worse t
han 0.28 W/m²k

Insulation product

Minimum
t
hickness

(
mm
)

Kingspan

Kooltherm K
12

or other approved with
a K value of 0.020
-
0.022

7
0


External timber framed walls with render finish
(
U
-
value

0.28

W
/m².k)

Render finish (to comply to BS 5262)
-

to match exi
sting or as specified to be applied in 3

coats at least 16mm


20mm thick overall to render lath

as detailed below
.
First &

second coats

1:3

(cement : sand with plasticizer). final coat 1:6 (cement : sand with plasticizer)
-

proportions by

volume. Render
should be finished onto an approved durable render stop, angle beads or

jointing sections
-

stainless steel or other approved using drilled or shot fired fixings only.


Stainless steel render lath fixed (using stainless steel staples) to vertical studs at
600mm max
ctrs. laps wired together at 150mm ctrs. (Mesh to be backed by a water resistant membrane) &
fixed to: Treated battens
-

25 x 50mm preservative treated battens fixed vertically to studs at max
600mm ctrs using 75mm long hot dipped galv or stainle
ss steel annular ring nails, fixed to:


Breathable membrane
-

‗Tyvek or similar approved suitable for timber framed walls to current
BBA certification, fixed to:

External quality plywood
-

12mm thick marine ply wood (or other
approved) fixed to:

Treated timb
er frame constructed using: 100/150mm x 50mm head & sole
plates and vertical studs at 400mm ctrs,