A 12x20 shed is a very large shed. It is on the boarder of being a garage. When building a shed the idea is to keep things simple but a shed as large as a 12x20 starts to complicate the construction process simply by the sheer size of the building. Everything from the foundation to the roof becomes more complicated. The roof trusses for a 12 foot wide shed need a few extra additions to make sure that they are strong and adequately cover the shed. There are a few construction techniques that can make the trusses for larger sheds stronger. It is easiest to explain these shed building techniques while describing the various parts of a roof truss.
The Truss Top Chord
Every roof truss has a board at the top that supports the roof decking. This board is called a top chord. The angle of this part of the roof truss is determined by the slope of the roof.
The Truss Bottom Chord
The bottom of the truss rests on and reaches from wall to wall. The truss top chord typically rests on the bottom chord. The two chords are attached to each other using a gusset.
A truss gusset is the plate that holds the truss members together at their connections. When building trusses on the job site the gusset is usually made using pieces of ½” O.S.B. cut several inches larger than the truss chords so the joint can be adequately covered and nails can be put through the gusset into the truss chords. There are three key points to remember when attaching gussets.
- Make sure that the gusset material is substantially larger than the joint so that the nails do not split out the truss members.
- Make sure that a gusset is placed on each side of the truss joint, like a truss sandwich.
- Make sure that the nails are far enough from the ends of the boards so they do not split out and weaken the wood.
Truss King Posts
When building trusses for the larger span that a 12x20 shed requires it is important to install a kind post in the center of the truss. The king post is attached to the truss using a gusset just like all the other connections. This important structural member is simply a piece of 2x4 lumber that is centered on the truss and is installed directly under the ridge down to the bottom chord. The top is cut with the angles of each side of the truss and the bottom is flat to sit on top of the bottom chord.
If each of these truss parts are used correctly the larger trusses needed for a 12x20 shed plan should have plenty of strength to handle regular roof loads. If your area has extreme weather conditions like heavy snow loads or high winds you should consult a structural engineer and your local building department to find out if there are other design elements that need to be added to your large shed design.
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