The Double Hip Roof Area calculator computes the
surface area of a hip roof with a hip roof dormer based on the dimensions.
INSTRUCTIONS: Choose units and enter the following:
- (S) Span of Main Hip Roof
- (L) Length of Main Hip Roof
- (θ) Pitch of Main Hip Roof (choose pitch from list)
- (R) Span of Dormer
- (K) Length of Dormer
- (Φ) Pitch of Dormer Hip and Sides
- (OP) Out Put (AREA or DETAILS)
Hip Roof Area (sA): The calculator returns the total surface area in square feet (ft2). However, this can be automatically converted to compatible units via the pull-down menu. If DETAILS are chosen, the calculator also returns the following:
- estimated number of 4x8s sheets to cover roof
- number of standard bundles of shingles (33.3 ft2) to cover roof
- number of ridge bundles of shingles (25 ft per bundle) for the main roof ridge, the four main roof hip ridges, the dormer ridge, and the two dormer hip ridges.
- the length of valley flashing (2 x dJ in the drawing below)
- number of roofing nails for both normal and high-wind conditions.
The Math / Science
A hip roof is basically a rectangular trapezoid volume has regular trapezoids in the front and back and triangles on the sides. The bottom and top rectangles are centered, form parallel planes and separated by the height. The complication of the hip roof dormer introduces the intersection geometries. All of the lines have to be computed based on the specified lengths and pitch angles. Fortunately, trigonometry wins!
The total surface area is the area of the main hip roof plus the dormer sides (tan) and end (green), minus the end of the dormer that covers part of the main hip roof (red).
Roof Types
