In this HowTo we will cover the 4 basic parts of a house structure.

Yes I know you are saying there are so many items in a house how can it be 
brought down to just 4 main parts. Well here we will be covering the 
structure
of the home better known as the Framing.

Framing can be thought of as the shell or skeleton of the home. Parts of it 
are made of Dimensional Lumber such as 2×4's, Beams, Plywood and others that
we will group into this category for now include the Foundation walls. What 
we are trying to understand is what gives our house its shape and stability
on which all other items rely.

The four basic parts are

Vertical Supports
Horizontal Supports
Sheathing
Decking

Lets start off with Vertical Supports.
This group includes all the items that give the height  of the structure and 
distribute loads from the top of the roof all the way down to the ground the
home sits on.

The Footing At the bottom of our house and the first thing to be installed 
is our footing. This is usually a 1 foot tall by 2 foot wide continuous 
block
of concrete that runs around the outside of our building. The footing 
transfers the load of the entire building into the soil so the soil it sits 
on must
be stable bedrock or highly compacted soil / gravel with no organic 
materials.

 As we travel up the side of the house we have the Foundation Walls. 
Foundation walls are usually made of poured concrete or block and rest on 
top of the
footing. The normal dimension is 8 inch width and will travel the whole 
perimeter of the building. If you are installing brick on the outside walls 
of
the home a ledge will be added to the top of the foundation wall for the 
brick to sit on. Foundation walls carry the total load of the house down to 
the
footing.

Posts and Stud Walls
Most people have seen a stud wall before but they may not understand how 
they work. On the perimeter of the home the stud wall is a load bearing wall 
this
means it will carry the loads of what is above it whether it is the second 
floor of the building or just the roof system. Although there are various 
methods
and materials used load bearing walls are usually made out of a bottom and 
top 2×4? plate which runs horizontal and Stud Grade 2×4's which have been 
tested
for quality to carry a specific load. The spacing between the studs in the 
wall is commonly 16 inches on center this means if you measure from the 
center
of the first 2×4 to the center of the next 2×4 they should line up at 16 
inches. This distance gives architects and builders a common understanding 
of
how much weight can be supported by that wall. In some instances such as a 
wall that will support hot tubs or pianos the architect may increase the 
width
of that stud wall or use a Post in the wall to support a beam.

Posts in wall system work just like posts on your outside deck. If you have 
taken a look under someones deck you will see 6×6 inch or larger posts that
are used for the vertical supports. Under decks we do not want to build a 
wall system that will inhibit traffic especially if its a second story deck 
so
we use a larger 4×4, 6×6 or 8×8 inch post that are set from 4 to 10 feet 
apart.

 Inside your homes walls you may see posts used around your Stairs or in 
great rooms that have a 2 story ceiling. More common is around windows and 
doors
such as your garage door or in a living room where there is a glass wall.

These posts will either be actual dimension or they can be built up with a 
series of 2×4s that are nailed together but no matter what type of post or 
stud
is inside your wall it is there to transfer loads to the foundation and then 
down to the footing.
Horizontal Supports

Horizontal supports are the load carriers for your floors and we are also 
going to include the roof trusses / rafters in this group.

As we just learned our vertical supports include stud walls and posts and 
also our foundation walls but without horizontal members everyone is going 
to
be living in their basement.

Horizontal supports include Joists, Beams, Headers and Rafters.

Joists are the long 2×12? pieces of lumber that span the distance between 
our outside walls. They look similar to a 2×4 stud wall laid on their side 
but
they are thicker because they need to carry loads from the center of the 
span / room out to the edge of the wall where the stud wall or foundation 
supports
it.

Joists are laid out in a similar pattern to a stud wall with a rim joist at 
the outside to provide lateral stability and to tie all the joists together.
They are also laid out 16 inches on center and they should line up within an 
inch or two with the studs in the wall below it.

In residential construction a common house width may be 30 feet but the 
longest practical 2×12? joist is about 16 feet. This means our home will 
need a
center load caring Beam.

Beams can be made of Steel, Dimensional Lumber or Glue Laminated products.

For small spans around stairways you will probably see a combination of Glue 
Laminated and Conventional Lumber with a plywood center.

Mid Span between our joists in the basement you will most often see a Steel 
Ibeam that can be resting on each end of the foundation or with center 
supports
for the beam made out of block, concrete or steel posts.

To support our second floor areas midspan you will most likely see 2 
conventional 2×12's with a center steel plate called a fletch plate to 
strengthen the
beam or you might see a steel ibeam or even a wood ibeam or glue laminated 
beam. It all depends on the weight it will support and its length.

In the Attic if you have a conventionally framed attic you will most likely 
have a 2×6 or 2×8 floor joist and the overhead rafters that support and form
the roof peak will be made from 2×6? lumber.

There are many products that can be used for both the Joists and the Beams 
and the selection is made by an architect that calculates loads.

The main idea is that the weight of the floor and all the contents of the 
home will travel out to the edge of the joist where it sits on top of a stud 
wall
or beam and then that load will take the total weight of everything and send 
it down to the foundation wall and into the footing.

Any place that you need to span an area and redistribute its load from a 
direct up and down vertical you need to use a Joist, Beam or Header.

Headers can be thought of as small beams that sit inside a stud wall to 
allow openings for things like windows and doors.
Sheathing

Sheathing is the part of the wall that gives it surface area. As we just 
learned the Studs or Posts in a wall are used to support the loads of things 
that
are above them either the second floor or roof.

Sheathing serves 2 purposes in walls on the inside of the stud wall we place 
drywall to give a nice appearance and living space. On the outside of the 
wall
we apply Plywood or a similar material like OSB to protect the home and to 
give lateral strength to the wall.

When you apply Plywood Sheathing to the outside of a home it comes in 4×8 
foot pieces. There is a directional structure in the plywood and on the face 
it
will tell you if you can apply it horizontally or vertically. For the most 
part it should be applied Vertically but in larger wall system 10 or 12 feet
in height the contractor may start with a half sheet at the bottom and then 
apply a full vertical piece above it.

When it is nailed to the plywood it is best if construction adhesive is also 
used but it is not totally necessary.

Nails should be 6 inches on center running up and down the stud wall which 
can be tricky since you can't see inside the wall. It is often best to check
the plumb and bow of a stud wall before you apply the plywood.

Some contractors will apply the plywood before lifting the stud wall 
vertical. This is a good solution if you have more then a few men to help 
lift the
wall. If not you can build the stud wall and then apply the plywood after.

Lateral Movement. The plywood helps stabilize the wall so that it will not 
fall down like a deck of cards in a storm or earth quake. It is important to
know your seismic stress loads for your location when building the stud wall 
and applying the sheathing because you may need to add additional bracing
or brackets.
Decking the final piece

Decking is the plywood that covers the joists to make up the floor.

Just like the joists are thicker then the studs in walls the Decking plywood 
material is thicker then the sheathing plywood that covers the outside of 
the
home. In new homes 3/4 inch plywood or OSB decking is used and it should be 
glued to the Joists. This is not a step that can be missed because without
the construction adhesive you will end up with squeaks and pops.

Another feature of Decking for floors is its Tongue and Groove. This makes 
positioning the plywood a little more difficult as you work the tongue into 
the
previous pieces groove but it is important because it locks the whole floor 
decking together in one piece.

In older homes you may find that they used boards instead of plywood this is 
not a problem because you can usually match up any area that needs to be 
fixed
with new plywood decking and at worst you can shim the joists with strips of 
2x material to get the proper level.
As we included rafters in the Horizontal Support system we also include the 
roof sheathing in the Decking because it supports both wind and snow loads 
it
needs to be handled a little different then wall sheathing.

Roof decking does not have tongue and groove ends and it does not need to be 
glued but it is important that you use 1/2 inch plywood instead of standard
OSB sheathing material because it will need to withstand much more rain, 
ice, wind loads and rot.

When you install the roof decking you should use clips between the 16? or 
24? spans  of the roof rafters to provide additional support.
We have gone over the highlights of the basic parts of the house structure.

There are many more options then can be handled in this overview and you may 
find that some of the methods are different in your home but for the most 
part
these 4 items make up the basic shell of your home.

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