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.

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