HausCraft

Gambrel roof calculator

Give it a width, a length and the two pitches. It frames a barn-style gambrel roof, steep below and shallow above, and lists every rafter.

ft
ft
in 12
in 12
in

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Building…

HausCraft
PieceSizeLengthHow many
Rafter2×611 ft 11 3/4 in26
Rafter2×65 ft 8 1/8 in26
Ridge board2×612 ft 11 1/2 in6
Barge rafter2×611 ft 11 3/4 in4
Barge rafter2×65 ft 8 1/8 in4
Lookout2×61 ft 7 1/2 in16
Corner rafter2×64 ft 3 15/16 in4
Sub-fascia2×612 ft 10 7/16 in4
Top plate2×49 ft 7 1/8 in8
Top plate2×45 ft 7 3/4 in8
Stud2×41 ft 10 in to 10 ft 3 7/8 in56

In all 2×4: 520 ft · 2×6: 703 ft

How it is worked out

  • Each side has two runs of rafters. A steep one rises from the wall to where the slope turns, and a shallow one runs from there to the ridge.
  • The slope turns a quarter of the building’s width in from each wall.
  • Where the two runs meet they butt a board along the turn, as the upper ones butt the ridge board at the peak.
  • Lower rafters are notched over the wall’s plate and run on to the overhang.
  • The gable ends are framed up to the roof in studs, and each rake has a barge rafter on lookouts.
  • What holds a gambrel’s shape, gussets at the turns or a floor across, is yours to add.

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 are the angles of a gambrel roof?
A steep lower slope near 60° with an upper near 30° is a common barn shape. This starts close to that, and both are yours to change.
Where does a gambrel roof break?
Here, a quarter of the width in from each wall. The height of the break follows from the lower pitch.
Does it draw the gussets?
It frames the rafters and the boards they meet on. Gussets and collar ties at the turns are yours to add.

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