The Purlins for a Roof calculator 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.
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).
See also, Metal for Roof to compute the number and length of metal roof panels.
The Math / Science
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.
Building Calculators
- Total Building Materials Calculator
- Metal for a Shed or Animal Run-in
- Purlins for a Shed or Animal Run-in
- Roofing Calculators
- Metal for a Roof - Calculates the number of metal panels for a roof.
- Area of a Roof - 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.
- 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.
- Shingles needed for a roof - Calculates the number of standard bundles (33.3 ft2) of shingles for 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.