How to Install Felt Underlayment for a New Roof

Once you have properly installed the plywood, flashing and freeze barrier to your roof, the next step is the felt paper. Installing the felt on your new roof will help the shingles to repel moisture as well as help to insulate the house. To properly install the felt paper only takes a little time, a few tools and a bit of know-how.

Things You'll Need

• Rolls of felt
• Button cap nails
• Small nail gun
• Compressor
• Razor knife
• Ladder
• Safety glasses
• Leather work gloves

Instructions

1. Roll the first layer of felt onto your roof. Begin at the bottom of the roof and roll out the felt. Cut the felt paper with your razor knife leaving a couple of inches extra on each side. Line up the felt paper so that the bottom of the paper hangs over the bottom of the roof 1 inch.

2. Fasten the felt to your roof. Shoot button cap nails into the felt making a row of three nails placed every 18 inches. Place these nails into the bottom two-thirds of the felt paper leaving the top one-third nail free.

3. Roll out the next layer of felt onto your roof. Leave an extra couple of inches on each end. Lap the second layer over the first by covering the first layer of felt by one-third. There are lines on the felt breaking it into thirds.

4. Line up the bottom of the second layer with this line and secure it to the roof by shooting button cap nails into the felt into the bottom two-thirds of the felt paper. Continue laying and securing felt paper with a one-third overlay to the peak.

5. Cut your felt paper so that it fits securely around any obstructions in the roof. When you get to the gap in the plywood at the peak of the roof be sure to end your felt paper even with the plywood so that it does not cover the space for the roof vent.

Tips & Warnings

• Leave the overhang on the sides and bottom until after the shingles are installed. The finished product will get trimmed evenly together after installation is complete.

• Working on a ladder or roof poses a fall hazard. Always use caution and common sense when working at heights. A safety harness and lanyard are recommended anytime a worker is more that 6 feet off the ground.

• Nail guns and other power tools run by a compressor are hazardous. Never disarm the safety mechanism in your nail gun. Please read and follow all of the manufacturer's recommendations before and during use of tools run by compressed air.

• Always wear proper safety equipment, such as safety glasses and leather work gloves, when using tools.

• Razor knives pose a cut hazard. Please use caution and common sense when using this, or any other knife.

References

• More Information on Roofing.