TradesHow this works
Underlayment and nails come off the roof area in squares, where a square is 100 square feet. Rolls are sized in squares of coverage, so the rolls you need is just the area divided by the roll's coverage, rounded up for overlaps. Nails scale per square with the shingle count and how many nails each shingle gets.
The tool gives the rolls for each underlayment and the nail count and weight for your area, then frames the two decisions: synthetic versus felt, where synthetic wins on coverage and durability for more cost, and standard versus high-wind nailing, where six nails a shingle is what holds the roof in a storm. Size from the sloped area, not the footprint, or use the roofing-squares engine to convert.
Common questions
How many rolls of underlayment do I need?
Divide the roof area in squares by the roll coverage. Synthetic underlayment covers about 10 squares a roll, #15 felt about 4, and #30 felt about 2, where a square is 100 square feet. A 2000 square foot roof is 20 squares, so it takes 2 rolls of synthetic or 5 of #15 felt, plus a little for overlaps.
Is synthetic underlayment better than felt?
Synthetic covers more than twice the area per roll, weighs less, and does not tear or wrinkle in wind and foot traffic before the shingles go on, which is why most roofers have switched to it. Felt is cheaper per roll up front. The tool shows the roll count for each so you can weigh the cost against the coverage and durability.
How many roofing nails per square?
About 320 nails per square at four per shingle, which is roughly 2.5 pounds of 1-1/4 inch roofing nails. In a high-wind zone or where the shingle warranty calls for it, you go to six per shingle, about 480 per square, and roughly half again as many pounds. The tool figures the count and weight for your area and exposure.
Sources: Roll coverage: synthetic 10 sq, #15 felt 4 sq, #30 felt 2 sq per roll (industry standard) · Shingle nails: ~320/sq at 4 per shingle, ~480 at 6, ~2.5 lb/sq (typical). Engine version 1.0.0. Risk tier 1.