Roofing Calc

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Calculator / Last modified by AndrewBudd on 2019/03/01 16:28
Area of a Roof Sheeting for Roof
Roof Pitch Sheathing Cost Estimate
Truss Count Shingles for Roof
Rafter Count Shingle Cost for Roof
Rafter Length Weight of Snow on Roof
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The Roofing calculator has equations and data items for simple gabled roofsroofer.pnggabled roof including trusses, roof area, roof sheeting, and shingles.   It will even tell you how much snow weighs on the roof.  

A simple gabled roof is commonly seen on Cape Cod or Colonial style homes, common sheds and barns.  Simple gabled roofs have rectangular and sloped faces.  This calculator currently does not support other styles of roofs with multiple valleys or blunted ends.

Roofing Calculator Functions:

  1. 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.  
  2. Roof Pitch:  This is the angle of incline in the roof in both degrees and rise over run (e.g. 26.6: 6/12) based on the length of the rise and run.
  3. Truss Count: This is the number of trusses needed based on the roof width and the truss spacing.
  4. Rafter Count: This is the number of rafters needed on one side of a gabled roof based on the roof width and rafter spacing.
  5. Rafter Length:   This is the length of rafters based on the pitch and the length of the span.
  6. 4x8 Sheeting for Roof: This calculates the number of 4x8 sheets needed to cover a roof.
  7. 4x8 Sheeting Cost Estimate: This is a rough cost estimate for the total number of plywood or OSB sheets to cover a roof.
  8. Shingles for Roof: This calculates the number of standard bundles (33.3 ft).  This includes the double row at the bottom of the roof-line.
  9. 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.
  10. Weight of Snow on Roof: This is the weight of snow on a roof based on the roof dimensions and the depth and type of snow.

Price Survey Data

One  should use the pricing for roofing materials that can be bought locally.  However, the following prices are for different quality grades of shingles in the United States:

All prices are for one bundle of shingles which covered 33.33ft2

This is only an estimate, and may vary based on the price of shingles that you purchase. Furthermore, it does not include the cost of ridge shingles, under cover (tar paper or felt), or other materials such as flashing, nails and glues.  

Gabled Roofs

220px-Gables.jpgA single-story house with yellow gables
A '''gable''' is the generally triangular portion of a wall between the edges of a dual- .  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. Thus the type of roof enclosing the volume dictates the shape of the gable. A '''gable wall''' or '''gable end''' more commonly refers to the entire wall, including the gable and the wall below it.

A variation of the gable is a '''', which has a stairstep design to accomplish the sloping portion.   Roof-Combined.png  One and two sided roofs 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, creating a force of lift on the  top of the roof. 



See Also