Sill Framing

solesudaneseUrban and Civil

Nov 25, 2013 (3 years and 9 months ago)

127 views

Floor Framing


Sill Framing



2 main functions of a sill
-

establish a straight, solid, level bearing surface
for the floor joists, and provide the member that can be bolted to the
foundation as a connection between concrete foundation and wood framing.

Balloon Style Framing

In Balloon Style Framing, t
he wall studs rest directly on the sill plate (in this
case a 2x8).


However, the studs rest outside the header/joist frame against
the outer wall.


Instead of the studs sitting on the floor joists, the stud
s sit
outside and run up the entire height of the house.

This
provides a sound framing;

however, it is more complicated

so it isn't used
as often for most houses.


NOTE:

This
is older c
onstruction. It made for quicker builds
but it was
dangerous when it

caught fire

because there was no break between floors.


Platform Framing

(Box
-
sill Framing)

The most extensively used sill framing in Canada.


Joists rest on the sill plate,
with the header board (both 2x8) framing the butt end of the joist.


The
sub
f
looring (usually 4’x8’ sheets of plywood) is

then nailed on top of the joists,
and a wall plate is nailed on top of THAT, with the wall studs being attached to
the wall plate.


The main advantage is that wall sections can be framed
separately

from the floo
r as one unit, and then attached once the floor is
finished.


This saves a lot of
time;

however there are now FOUR timber
members in the frame that may shrink over time, causing settling in the walls.




Floor Joists

Fun
ction of the floor joists

-

Support
weight of floor, walls, furniture and load
of residents, and tie together and stiffen the framework of the house.

The size and wood type of the joist affect how much load it can carry, so the
length and spacing of the joists will vary greatly.


Most common

wood type is
pine, and usually 2x8 joists are used.


They are usually spaced 16" apart, and
meet over a central support girder or beam.


This beam is usually made of 3
2x8s nailed together (and often laminated) that run parallel to the length of
the house
.


Most commonly, the joists overlap and are nailed together over the
beam.


This overlap must be a 3" minimum.


Also, joist hangers are becoming
more common, and they are nailed into the central beam and the joist rests in
its nest.


Also, a ledger board
may be used, which runs along the bottom end of
the beam, and the joist rests on it.


This is not seen as being as stable as a joist
hanger, or o
verlap, and is not used often n
owadays


Floor Rough Opening


Floor Trusses

Gaining a lot of popularity, pre
-
formed floor trusses are more solid, shrink less,
and are easier
to install that traditional floor joists.


Most houses use wood
trusses, but larger building would use steel.


The main advantage is ease of
install (you just place them and nail them, they come pre
-
formed), as well you
would need
fewer

trusses than joists
, and they do not need a central girder
support.


However, they are much more costly than constructing simple joists.





Bridging

If you are using joists, and

not trusses, you will need support
bridging

between
the joist members.


Bridging

provides stability and rigidity between joists, by
helping to prevent warpage when shrinkage occurs. Support
bridging

comes in
three main forms
-

solid, strap and diagonal.

Solid
bridging

is usually made from wood the same size and type as the floor
joists, often from scrap leftovers.


They are nailed at intervals between the
joists, and if you are using plywood sub
-
flooring, you will need solid
bridging

as
a horizontal membe
r to nail the edge of the plywood sheets to.

Strap
bridging

is made from thin metal straps that are wound from the top of
one joist to the bottom of the next, then up to the top of the next joist, and so
on until you reach the end, and then reverse the pro
cess.


The top and bottom
of the straps are nailed to the joist members.

Diagonal
/Cross

bridging

comes in two main types
-

wood and metal.


Wood
bridging
, or herringbone, are 2x2 or 1x3 stock that cross between two joists to
prevent twisting.


Metal diago
nal
bridging

is the same, except the bridge
members are made of metal.


Herringbone
bridging

is rarely used, as they are
more time consuming as the individual members must be cut to size, and then
have the ends cut on diagonal lines to fit into the opposit
e joists.


Most houses
use solid wood
bridging
.


Truss
-
constructed houses require no
bridging

members, as the trusses support the weight perfectly.


Horizontal wood pieces
many be used between trusses to provide the nailing surface needed for the
plywood s
ubflooring.










Subfloor Construction


The subfloor platform caps the foundation. It provides the base for
framing the walls and roof. Before start
ing, it's important to check
the squareness of the foundation perimeter by measuring diagonally
from the corners. This way, you know what you're dealing with. If
the distances aren't quite the same, repositioning the sills may be
necessary.



Setting Sil
l Plates

You usually need to drill holes in the sill plates so they'll fit over
the anchor bolts cemented into the foundation.

Transpose each
bolt location onto the sill plates by measuring in from the sill edge
and over from the sill end.

Drill the holes

and ream them just a bit larger than the anchor
bolts. This way, getting the sill plate started over several bolts will be easier. Also, put a
sill gasket under the plates to insulate and prevent air infiltration. You may even want to
caulk around both si
des of the plates.

Codes require using pressure
-
treated lumber sill plates.
Pressure
-
treated sill plates resist

wood rot that can be caused by close proximity to soil and moisture.

Depending on the project, local codes may require 2x6s or 2x8s. A wider sil
l plate gives
more room for the joists to set on and provides a larger nailing surface.

When all the sills are in place, toenail them together at the corners. Then snug the anchor
bolt nuts. After the floor joists are on, you can go back and cinch them do
wn tight.

NOTE:

When installing the sill plate, your plan may call for setting the exterior wall
sheathing flush with the outer foundation wall. So set the sill plates back the thickness of
the exterior wall sheathing.



Installing Rim

(Header)

Joists

Rim

(Header)

joists are next. If you're using joist hangers, nail those
to the rim joists before setting them in place.

On top of the sill plates, set the rim joist boards on edge
--

flush with
the outside edge of the plates
--

and toenail the rims inwar
d into the
sill plates.

Then check the work again. Measure the span between the side joists at both ends and in
the middle. Make sure the distances are correct
--

so the floor joists will fit. Once the rims
are set, nail them together at the corners.



Se
tting Beams

If the floor system is wider than can be accommodated with a single
span of lumber, an intermediate beam or a bearing wall may be
necessary. Beams are usually steel I
-
beams or laminate veneer
lumber (LVLs).

NOTE:

Some beams required renting
a crane &
operator.

The ends of some beams set in pre
-
made notches in the foundation block so
the beam sets flush with the foundation top. Other beams may set on top of
the foundation. If this is the case, you may be able to nail on joist hangers to
the b
eam to accept floor joists.

After the beam is installed, you may need to install steel posts (on concrete
footings) under the middle of the beam for additional support.



Installing Floor Joists

Floor joists are usually spaced on 16" center. Floor joist
s run
perpendicular over a beam and overlap or butt together over it
--

and
sometimes joists fit in hangers fastened to the beam's sides, instead
of setting on the top.


If you're using joist hangers, installing floor joists can simply mean dropping them
in
place.

Fit the floor joists in the hangers nailed to the rim joists (and beam if you have one).
Hanger brackets can really save you time, but they can get nailed on crooked, so make
sure the joists are level to each other across their tops.

If you're
not using joist hangers, toenail them directly to the rim joists.

NOTE:

Any floor joists that have a crown (bow) in them should be installed crown up.
Over time, the crown will straighten out.

While there's still good access to the floor joists (before
the
decking goes on), install the
bridging
. Fasten
bridging

at the
mid
-
point of the joist span, between the floor joists, to give them
stability and to prevent the floor from squeaking.

The extra weight of the floor joists push the sill plate down and
exp
ose a few more threads on the anchor bolts. So once the joists are installed go back
and tighten down the anchor bolt nuts.



Fastening Subfloor Decking

Next the actual floor "decking" can go on. It's also called the
subfloor. It's usually 3/4" plywood.

Utilize the factory
-
cut edges at joints when possible. And carefully
try to get straight cuts so when you do use a scrap piece with a cut
edge the joints fit together nicely.

N
OTE
:

When installing any plywood decking, stagger the joints and
leave a

gap
o
f about
1/32"
in the sheets
to allow for expansion due to moisture.

Use construction adhesive and subfloor nails or screws to secure the sheets to the floor
joists.

TIP:

For an even stronger, more stable floor, special subfloor materials are now
availabl
e. These are slightly thicker than standard plywood and have tongue and groove
joints.


Floor Framing Questions

This information will be on future tests/quizzes and the exam.

1)

What is the function of a girder?


2)

From what materials are girders usually made?


What is the most
common method of making girders from residential use?


3)

What are the two main functions of a sill?


4)

Find a definition, and draw a diagram showing

Balloon Framing and
Platform Framing.


5)

What is a floor joist for?


What does it do?


What si
ze board are most
floor joists made from?


6)

Draw a diagram showing how floor joists are commonly hung


7)

What purpose does the header board serve?


8)

What is an improper way of hanging a floor jois
t?


Why is it a bad idea
to hang

joists across the whole length
of the floor?


9)

What are trimmer joists?


10)

How far apart do most common floor joists have to be?


11)

Draw a diagram showing the most common method of framing floor
openings?


12)

What are THREE common types of
bridging
?


What materials are
bridging

commonly made fr
om?


13)

What is the purpose of
bridging
?


14)

What is the most common material used for laying subflooring?


15)

Name at least FIVE problems with improperly laid joists and
s
ubflooring.


16)

What is a crown? How should the crown be laid?


17)

What is the main purpose

of the

subfloor?


18)

Describe, in a paragraph,

the steps involved in
construct
ing

a
subfloor from scratch.