The Purlins for a Roof calculator 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.
INSTRUCTIONS: Choose units and enter the following:
- (L) Ridge Length (Note: this should include rake overhang)
- (S) Roof Span
- (P) Roof Pitch
- (oH) Overhang
- (PoC) Purlin On-center spacing (default: 24")
Purlins for a Roof (RP): The calculator returns the number and length of purlin rows for the roof. To calculate the number of boards needed for purlins, divide the length of the purlin rows by the length of boards you are using (e.g. two boards of length eight feet for each 16 foot long purlin row).
Purlin and Girt Calculators
- Purlins for a Gabled Roof
- Purlins for a Hip Roof
- Purlins for a Shed Roof
- Purlins and Girts for a Shed
The Math / Science
A gable roof is the most recognized shape of a roof. It has a ridge down the middle and two equal area sloped sides. Roofing material is needed for the sides to prevent water from entering into the building.
The Purlins for a Roof calculator is meant to help with material estimates for a metal roof. Purlins are typically 1"x4"x12' boards, sometimes called furring strips, that are used under metal roofs. They are typically untreated wood since moisture should be blocked by the roofing material. In all cases, confirm your estimates with a professional estimate and adhering to local building codes.
The calculator uses the ridge length for the length of the purlins. The spacing is used with the total rise and run to compute the number of purlins.
Roof Calculators
- Gabled Roof
- Hip Roof
- Shed Roof
- Dormers
Building Calculators
- Total Building Materials Calculator
- Pitch of a Roof - Computes angle of incline in the roof in both degrees and rise over 12" run (e.g. 26.6o : 6/12) based on the length of the rise and run.
- Number of Trusses Needed for a Roof - number of trusses needed based on the roof width and the truss spacing.
- 4x8s needed for a roof - Calculates the number of 4x8 sheets needed to cover a roof.
- Roofing nails needed for a roof - Calculates the number of roofing nails needed for a roof in normal and high wind conditions.
- Number and Length of Metal Roof Panels - Computes the length and number of metal panels and trim pieces for a metal roof.
- Screws for a Metal Roof - Computes the number of screws needed for a metal roof.
- Number and Length of Purlins for a Roof - Computes the number of purlins for a roof based on dimensions and spacing.
- Number and Length of Rafters - Computes the number and length of rafter boards based on roof dimensions and spacing.
- Number and Length of Rafter and Collar ties - Computes the number and length of rafter ties and collar ties based on roof dimensions and spacing.
- 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
Roofing Geometry Calculators