The Purlins for a Gambrel Roof calculator computes the length and number of rows of purlins needed for a gambrel roof based on the dimensions. 
INSTRUCTIONS: Choose units and enter the following:
- (L) Ridge Length
- (S) Span of Roof
- (P1) Lower Pitch
- (P2) Upper Pitch
- (LH) Loft Height
- (oH) Overhang
- (PoC) Purlin Spacing
Gambrel Roof Purlins (nP): The calculator returns length and number of rows of purlins, and the total board length of purlins for a gambrel roof. The lengths are returned in feet can be automatically converted to compatible units via the pull down menu.
Purlins and Girts
Purlins are rows of boards nailed horizontally to a roof's frame to act as a base for surface materials such as a metal roof panels. Purlins are usually nailed but sometimes screwed to rafters or trusses and spaced in horizonal rows. The metal roofing panels are then screwed onto the purlins vertically forming the roof up to the ridge cap and down to the drip edge of the overhang.
Girts are like purlins and used on walls to be the base of metal panels for siding. 
Girts are horizontal boards nailed or screwed to vertical posts or studs, and they are used as the support structure to vertical wall panels such as metal siding. Girts are often 2x6 boards.
Gambrel Roof Calculators
- Gambrel Roof Surface Area: This computes the total surface area of a gambrel roof, and the number of 4x8s and bundle of shingles needed for a roof based on the dimensions below.
- Trusses Needed for Roof: This computes the number of trusses needed for a roof based on the ridge length and spacing.
- Sheathing for Gambrel Roof: This computes the number of 4x8 sheets to cover a gambrel roof based on the dimensions of the roof. It also includes the number of framing nails needed to nail the sheets to the roof based on whether clips are used or blocking.
- Gambrel Roof Shingles: This computes the number of bundles of shingles and ridge shingles needed for a gambrel roof based on the dimensions and bundle coverage.
- Roofing Nails for Gambrell Roof: This computes the number of roofing nails to shingle a gambrel roof based on the dimensions and wind conditions.
- Underlayment for Gambrel Roof: This computes the total surface area of a gambrel roof for underlayment based on the dimensions below and the estimated cost based on the area and unit price of underlayment material
- Purlins for Gambrel Roof:
This computes the length and number of rows of purlins needed for a gambrel roof based on the dimensions - Metal Panels for Gambrel Roof: This computes the length and number of vertical metal panels needed for a gambrel roof based on the dimensions. It also provides the length of the trim pieces.
- Horizontal Siding for Gambrel Wall: This compute the number of horizontal siding panels (e.g., vinyl or cedar) for a wall under a gambrel shaped roof line.
- Screws for Gambrel Metal Roof: This computes the number of screws to attach metal panels needed for a gambrel roof based on the dimensions. It also includes the total square feet and the number of metal screws needed at 0.75 screws per square foot.
- Metal Panels for Gambrel Wall: This computes the number of vertical siding panels, their lengths and the total length of vertical panels on a wall under a gambrel roof. It also includes the total square feet and the number of metal screws needed at 0.75 screws per square foot.
- Gambrel Pitch Angles: This computes the upper and lower pitch angles and rafter lengths bases on the span, total height, and height and width of the loft.
- Gambrel Rafter Lengths: This computes the upper and lower rafter lengths, loft width and total height based on the upper and lower pitch, span and loft height.
- Gambrel Angle: Compute the interface angle where the two pitched surfaces meet on the roof.
- Screws for Metal Siding Gambrel End Wall: Computes the number of metal panel screws needed for vertical metal panels on a wall under a gambrel roof.