How Much Roofing Underlayment Do I Need

Underlayment should cover the entire roof deck.

How much roofing underlayment do i need. So covering 240 squares would require 60 rolls of underlayment. The average roll of 15 pound roofing felt covers about 400 ft 2 or 4 squares while the average roll of 30 pound roofing felt covers about 200 ft 2 or 2 squares. Inquire at the hardware store regarding the amount of underlayment nails required. If you are installing synthetic underlayment 6 inch overlap is sufficient.

Rubberized asphalt roofing underlayment should be added at valleys and around roof protrusions. While it is possible to estimate the amount of necessary materials using only the total roof area measurement as can be seen from the table depending how large the pitch of the roof the actual area of the roof can differ by up to 2 236 from the measured total area at a pitch of 24 12. So in the gable roof example above you would need 240 squares of underlayment. It is advisable to use plastic cap nails to fasten down the underlayment with 12 inches on center spacing at the top and bottom of each course.

Gcp applied technologies grace ice water shield roofing underlayment requires side laps to be a minimum of 90 mm 3 5 in and end laps a minimum of 150 mm 6 in. These spots often get leaky first. For a new roof you will also need the same amount of underlayment. The underlayment protects the edge of the roof deck from water damage.

Always use 1 in 2 5 cm nails. Underlayment usually comes in rolls of 4 squares each. This correction factor will take into account the greater area of the roof due to the pitch. Why do you need roofing underlayment.

Minimum overlap guidelines are set by the manufacturer. Roofing underlayment or felt is usually required for the ul fire rating to apply since shingles are usually tested with underlayment. The nails should be 12 inches 30 cm apart along the edges and 24 inches 61 cm apart in the middle of the underlayment strip. Consider other underlayment options as needed such as rubber or tar products.

Multiply the total area determined in step one by a correction factor to account for the roof pitch. If your roof pitch is 3 12 or 4 12 multiply by 1 25. 1square of roofing covers 100 square feet of roof a bundle is 1 3 of a square. There is a direct connection between membrane performance and proper application.

No underlayment is needed if you are applying shingles directly over an existing asphalt roof. The roof deck should be sound and level before laying the underlayment. For roof pitches of 5 12 to 7 12 use a factor of 1 3. Get the square footage of roof and divide it by 100 and it will give the number of squares you need and for every decimal number over 3 buy a bundle to achieve the amount of material.

Rolls of felt are 36 wide x 144 long for 15 and 72 long for 30. Fifteen pound or heavier felt underlayment is required by code in some areas.