The Gable Roof Geometries calculator computes the lengths and measurements for a gabled roof based on the ridge length, pitch, span and overhang. Measurements include rafter length, rafter board length, angle of roof, rafter cut angle, soffit and facia plate width, length of ridge board, length of rafter ties and collar ties and the total surface area.
INSTRUCTIONS: Choose units and enter the following:
- (L) Ridge Length
- (S) Roof Span
- (P) Roof Pitch
- (CD) Collar Tie Drop (default: 24")
- (oH) Overhang (default: 12")
- (oC) Rafter Spacing (default: 24")
- (BW) Width of Rafter Board (default: 5.5" for 2x6)
Rafter Boards (RB): The calculator computes the following rafter framing materials:
- (RL) Rafter Length
- (BL) Rafter Board Length
- (θ) Angle of Roof
- (α) Rafter Angle
- (f & s) Soffit and Facia Plate Width
- (R) Length or Ridge Board
- (nRB) Number of Rafter Boards
- (RT) Length of Rafter Ties
- (CT) Length of Collar Ties
- (SA) Surface Area of Gable Roof
The Math / Science
The Roof Rafter calculator is meant to help with material estimates. In all cases, confirm your estimates with a professional estimate and adhering to local building codes.
The rules in this calculator are as follows:
- The length of the Ridge is the length of the ridge plate
- The choice of rafter boards is 2x4 for rafters shorter than six feet (6'), 2x6s for rafters between 6 feet and 10 feet, and 2x8s for up to 16 foot long rafters. Consult your local codes for the required material specifications.
- Collar ties are included when the total rise is above 48".
Rafter ties or Ceiling Joists keep the rafter boards from kicking out under the downward load on the roof. Collar ties are suggested for roofs with a rise greater than forty eight inches (48"). There is one collar tie per rafter. Note: some builder use a collar tie on every other rafter. The collar tie length is a function of the pitch of the roof and the position of the collar tie. This algorithm puts the collar tie two feet below the ridge, but only if the ridge is 48" above the rafter ties.
Gable Roof Calculators
- Gable Roof Area: This computes the surface area of a gable roof based on dimensions and pitch.
- Trusses Needed for Roof: This computes the number trusses need for a roof including gabled roof.
- 4x8 Sheathing for Gable Roof: This computes the total surface area of a roof, the number of 4x8s and framing nails needed for a gabled roof based on the length, span, pitch and overhang.
- Gable Roof Sheathing Cost: This computes the number of 4x8 sheets (32 ft² each) needed to cover a gabled roof based on the ridge length, roof span, overhang and the pitch and applies the unit cost of a 4x8.
- Nails for Gable Roof Sheathing: This computes the approximate number of nails needed to nail 4x8 sheets to trusses or rafters on a roof based on the dimensions of the roof, spacing of nails on the edges and field of the 4x8, and whether blocking or clips are use.
- Purlins for Gable Roof: This computes the total number and length of purlins for a simple gable roof based on the ridge length of the roof, the roof pitch and the span of the roof.
- Metal for Gable Roof: This estimates the metal panels and trim needed for a metal roof for a simple gabled roof based on the roof dimensions.
- Metal Screws for Gable Roof: This computes the number of special screws needed for a metal roof.
- Shingles for Gable Roof: This computes the number of shingles (bundles), underlayment, ridge shingles, starter strip, and roofing nails for a gable roof.
- Gable Roof Shingle Cost: This estimates to shingle a basic gable roof based on dimensions (length, span, pitch and overhang) and the unit price of a bundle of shingles.
- Underlayment for Gable Roof: This estimates the cost of underlayment to cover a basic gable roof based on the area of a roof computed from the dimensions (length, span, pitch and overhang) and the unit price underlayment material.
- Roofing Nails for Gable Roof: This estimates the number of roofing nails needed for a common gabled roof based on roof dimensions and wind conditions.
- Rafters for Gable Roof: This computes the total number of rafter boards (roof joists) for a gabled roof based on the ridge length, pitch and span. It also returns the length of the ridge board, and the length and number of rafter ties and collar ties.
- Rafter Length: This computes the length of the rafters based on the span, pitch and overhang.
- Gable Roof Geometries: This computes the length of rafters, pitch and cut angles, soffit and facia base widths of a gable roof.
- Weight of Snow on Roof: This computes the weight of snow on a gable roof based on roof dimensions, depth and type of snow.
Building Calculators
- Area of a Roof
- Pitch of a Roof
- Number of Trusses Needed for a Roof
- 4x8s needed for a roof
- Shingles needed for a roof
- Number and Length of Metal Roof Panels
- Number and Length of Purlins
- Number and Length of Rafters
- Number and Length of Rafter and Collar ties
- Number and Length of wall top and bottom wall plates
- Number of Studs for a Room
- Number of Studs in a Wall
- Room Interior Area (wall and ceiling)
- Cubic Feet in a Room (volume)
- Number of 4x8 or 4x12 Sheets for a Room
- Number and Length of Floor Joists
- Number of Joist Hangers
- Compute the Cost of Floor Joists
- Compute iJoists for larger floors
- Compute the Number of 4x8 Sheets to cover the Deck or Floor
- Compute the number of Decking Boards to cover the deck or floor
Roof Types
