Roof truss calculator

How it is worked out

• Every truss is in one plane, with two top chords up to the peak and a 2×4 bottom chord on edge from the outside of one wall to the outside of the other.
• Its heels sit on the outer edge of the walls’ plates, and it spans the building from wall to wall on its own.
• A web stands plumb under the peak, with more between so each panel of the bottom chord is 6 ft or less. A diagonal crosses each panel, which makes a king post truss where there is one web and a Howe truss where there are more.
• The eaves are framed as a rafter roof’s are, with a sub-fascia along each and a barge rafter up each rake on lookouts.
• The gable ends are framed in studs.
• Trusses span one rectangle of walls. A roof too low to fit a web is turned down, and we say why.

We lay out and count the sizes you pick, close enough to plan a weekend and price the lumber. Span tables, your local code and, on a bigger job, an engineer settle what size each board has to be.

Questions

How many trusses do I need?

One at each spacing along the building’s length, and one more to finish. The list counts their chords, with two top chords to a truss and a bottom chord that comes in two lengths where it is longer than a 20 ft board.

What kind of truss is this?

A king post truss on a short span, and a Howe truss, with plumb webs and diagonals between them, on a longer one.

Can I build trusses from this?

It is made for planning and counting. The trusses that go on a roof come engineered from a truss maker, who sizes the plates and members from numbers like these.