How do you design a basic wood roof truss?


Quick Answer

To design a basic wood roof truss, place a joist member at the bottom. Two raft members attach to the joist member and meet in the middle in order to create a triangle. Depending on preference and functionality, either the raft or the joist should overlap each other to create the roof's eaves. For support, two diagonal braces are inserted between the joist and raft members.

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Full Answer

Before building a basic wood roof truss, determine if the plans meet the municipalities building codes and if the structure will withstand wind and snow. Select kiln-dried or seasoned 2-inch by 4-inch lumber, preferably straight in both grain and appearance, to construct the truss.

Place boards on a flat surface in the shape of the truss. Place the raft members on top of the joist member and mark which area of overlap to trim. Use a speed square and the pitch of the roof to determine the angle at which the area where the raft members meet should be cut.

Determine the positioning of the diagonal braces by dividing the total length of the joist member by three. Starting from each edge, measure the result; these spots are where the braces will reside. Use one of each member and the braces as patterns to cut subsequent sides of the roof truss.

Assemble the truss using nails, and reinforce each connection with a metal or plywood joint. Do the same for other trusses, and then stack them on top of each other to make sure they align. Once alignment is confirmed, the truss is ready to be installed on the roof.

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