Our Structures (4parts)

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The Structure of our homes

The structure better known as 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

Let’s 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 some ones 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 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 beam 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 beam or even a wood beam 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 we 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 your home.
 

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