Shed roof calculator

How it is worked out

• One run of rafters slopes from the low wall up to the high one, at the spacing you choose.
• The high side is raised on a short framed wall on top of its own wall, with studs 16 in on centre under a plate, as tall as the pitch needs.
• The two end walls are framed up to the slope the same way.
• Each rafter is notched over the plate at both walls, and runs on past each to the overhang.
• A sub-fascia closes the rafters’ ends at the low eave and the high one, and a barge rafter on lookouts runs up each side.
• A rafter that would need to be longer than a 20 ft board 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

What pitch should a shed roof have?

Your roofing decides. Shingles want a steeper roof than metal or a membrane does, and the maker of yours gives the least pitch it is good for.

How much taller is the high wall?

The pitch times the distance between the two walls’ plates. It is given above the list.

Is this a lean-to?

It frames a shed roof on four walls of its own. A lean-to against a house is the same slope with the house’s wall as its high side, where a ledger carries the rafters.