Gable Roof Calculator

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The Gable Roof Calculator has equations and data items for a common gabled roof including trusses, roof area, roof sheeting, shingles and underlayment.

This roofing calculator provides simple calculations that are useful to roofers and homeowners:

Area of a Roof: This computes the area of a roof based on the pitch and the dimensions of the area covered by the roof. It also returns the number of 4x8 sheets to cover the roof, the number of standard bundles of shingles to cover, and the number of roofing nails for both normal and high wind environments.
Roof Pitch: This is the angle of incline in the roof in both degrees and rise over run (e.g. 26.6^o: 6/12) based on the length of the rise and run.
Truss Count: This is the number of trusses needed based on the roof width and the truss spacing.
Rafter Count: This is the number and length of rafters needed based on roof dimensions and pitch.
Sheathing for Roof: This calculates the number of 4x8 sheets needed to cover a roof.
1. Sheathing Cost Estimate: This is a rough cost estimate for the total number of plywood or OSB sheets to cover a roof
Shingles for Roof: This calculates the number of standard bundles (33.3 ft² for 3-tab or 32.8 ft² for architectural shingles), ridge cap, underlayment, starter stirp and roofing nails.
1. Shingle Cost Estimate: This is a rough estimate on the cost of shingles for a roof based on the roof dimensions and price point ranging from economy (low budget) to premium.
Metal for Roof: This computes the total number and length of metal panels needed for a roof based on the ridge length of the roof, the roof pitch and the span of the roof.
Purlins for Roof: This computes the total number and length of purlins (roof support boards) based on the ridge length of the roof, the roof pitch and the span of the roof.
Underlayment for Gable Roof: This computes the amount of underlayment material needed for a gabled roof.

Gabled Roofs

A gable is the generally triangular portion of a wall between the edges of a dual sloped roof. The shape of the gable and how it is detailed depends on the structural system used (which is often related to climate and availability of materials) and aesthetic concerns. The two most common applications of a gabled roof are using either roof trusses or roof rafters. Both translate the load (weight) of the roof material and anything laying on it (e.g., snow) across the open space of the building to the walls.

A variation of the gable which has a stairstep design to accomplish the sloping portion. Crow-stepped gables were used in and as early as the seventeenth century. Examples of the crow-stepped gable can be seen at and , both 17th century Scottish buildings. Other early examples are found in parts of Denmark and Sweden.

Gable ends of more recent buildings are often treated in the same way as the Classic form. But unlike Classical structures, which operate through , the gable ends of many buildings are actually bearing-wall structures. Thus, the detailing can be ambiguous or misleading.

Gable style is also used in design, with varying degree sloped roofs, dependent on how much snowfall is expected.
Sharp gable roofs are a characteristic of the Gothic and classical Greek styles of architecture.

The gable end roof is a poor design for hurricane regions, as it easily peels off in strong winds. When wind flows over a gable roof, the surface behaves like a wing. Lift is created on the top of the roof.