Saltbox roof calculator

How it is worked out

• The ridge sits off the middle. Short rafters rise steeply from the front wall to it, and long ones fall from it to the back wall.
• Both walls are the same height, so the back slope’s pitch follows from where the ridge is. It is given above the list.
• Rafters are notched over the plate on each wall and run on to the overhang. They butt a ridge board along the peak.
• The gable ends are framed up to the roof in studs, and each rake has a barge rafter on lookouts.
• A back 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 is a saltbox roof?

A gable roof with its ridge off the middle, so one slope is short and steep and the other long and shallow.

How do I get a lower back wall?

Many saltboxes drop the back wall a storey. This one keeps both walls at one height and gets its long back slope from the ridge sitting forward.

Why was my roof turned down?

Most often the back rafter would be longer than a 20 ft board. Moving the ridge toward the middle or narrowing the building brings it back.