Purlins for Dormers

The Purlins for Dormers calculator computes the total number and length of purlins (roof support boards) for needed for one or more roof dormers based on the dimensions.

INSTRUCTIONS: Choose units and enter the following:

• (DD) Dormer Depth
• (DW) Dormer Width
• (P₂) Pitch of Dormer Gable (choose pitch from list)
• (P₁) Pitch of Main Roof (choose pitch from list)
• (n) Number of Dormers
• (pS) Purlin Spacing

Purlins for Dormers (PRLN): The calculator returns:

• (TA) Area: Total surface area of dormer(s) in square feet.
• (nP) Number of Rows : Number of rows of purlins on a single dormer.
• (pL) Purlin Length: For each row (both sides), the length of the purlin. 
• (TBL) Total Board Length: The sum of the lengths of the purlin boards

Items with units can be automatically converted to compatible units via the pull-down menu.

The Math / Science

Dormer Calculators

• Surface Area of Dormers: This computes the roofing surface area for dormers based on the dimensions and number of dormers.
• Metal for Dormers: This computes the metal roof materials (panels, ridge cap and trim) for one or more roof dormers based on the dimensions
• Screws for Metal Dormers: This computes the number of metal panels screws needed for one or more roof metal paneled dormers based on the dimensions.
• 4x8s for Dormers: This computes the number of 4x8 sheathing needed for one or more roof dormers based on the dimensions.
• Shingles for Dormers: This computes the number of shingle bundles needed for one or more roof dormers based on the dimensions. It also includes ridge shingles, valley lengths for flashing, and roofing nails.
• Underlayment for Dormers: This computes the amount of underlayment needed and estimates the cost of underlayment materials.
• Roofing Nails for Dormers: This computes the number and weight of roofing nails needed for one or more roof dormers based on the dimensions.
• Purlins for Dormers: This computes the total number and length of purlins (roof support boards) for needed for one or more roof dormers based on the dimensions.
• Dormer Geometries: This computes the diagram measurements for a dormer based on the dimension.

Roof Types

Roofing Calculators