For decades roofers have fitted a layer of felt over a roof s sheathing or roof deck before installing shingles.
Two layers of felt on roof.
Most often made out of plywood this roof layer is installed over the framing in a typical roof install.
Apply another layer of adhesive to the top for maximum waterproofing.
On 4 12 or greater slopes the balance of the roof shall be one layer of 15 felt.
You can cover the surface of the felt with gravel for added strength.
Though the requirement is 2 layers 15 felt in my area northern california the roofers spec 30 whether for 2 layer low slope or 1 layer normal high slope.
Why use roofing felt paper.
Add the second layer.
Assuming your roofing contractor is using standard 36 wide 15 roofing felt double coverage means that each layer of felt put down across the roof laps 19 over the upper half of the previous course.
This will help the two layers adhere to each other.
Saving on the initial shingle installation doesn t solve the long term cost of adding a second layer of shingles.
So anywhere along the gable end that you can see the felt you ll see two layers.
I am aware of the best practise of at least one layer of underlay nailed to the deck before a cap sheet is glued to the top with cold adhesive.
On roof slopes of 2 12 to 4 12 the remainder of the roof shall be two layers of 15 felt applied in shingle fashion or 1 layer of ice dam protection.
Two layers of shingles trap more heat which in turn damages the shingles and shortens the life span of the roof.
The key to weatherproofing your flat roof is adding a total of 3 layers.
It provides backup protection in the event of ice or water damage.
If i were you i d at least follow up with that roofer on why they chose to spec 2 layers felt just for piece of mind and in case he turns out to be the better roofer or not.
Wind driven rain or snow can trap water under your shingles putting your roof deck and inner residence at risk of moisture.
I have been supplied with way too much felt.
The first course starts with an extra 1 2 wide run.
In northern climates ice or snow dams are another common.
It provides structure by tying.
It didn t come with any underlay but i have worked out i could felt the roof twice with the cap sheet felt they have supplied.
Cover the edges of the roof with strips of felt before laying out the final layer.
Here are the layers of a roof in order of application bottom to top.
Roofing felt offers an additional layer of protection against the elements.
You will follow the same process as in step 2 for the last layer.
