I added a room to the side of my house, and the new roof goes onto the existing roof. I am almost done roofing it. The image below depicts the current status. I put roofing felt down under the two rows of the existing shingles as shown in the image. I have a roll of aluminum flashing that I plan on putting over the felt at the roof intersection where there is about a 1/2" drop from the new roof OSB to the existing roof. After that I have just one more row of rolled roofing to install. Here are my questions.

  1. Does the new felt go far enough under the shingles?
  2. Should the flashing cover the end of the new felt as well as the intersection?
  3. How far under the shingles does the rolled roofing need to extend?
  4. How do I attach the flashing and rolled roofing under the shingles?

I'm thinking that I would lift up the second or third row of shingles and nail under them with the rolled roofing in place.

enter image description here

1 Answer 1

  1. The new felt should go under the old felt.

  2. The new flashing should go under the old felt and over the new felt and new roll roofing.

  3. Depends on the slope of the new roof. The lower the slope the further it should extend.

  4. Roofing nails to the existing structural sheathing.

The big idea is that layers of the lower roof should sit below corresponding layers of the upper roof. That is:

  • Everything should lap just like shingles.

  • Nothing should back-lap.

  • The flashing should double lap the roll roofing.

  • Even though the higher roof was installed first, the end result must be the same as if you started at the eave and worked all the way to the ridge.

  • Thank you. I wast thinking that would be the best way to do it. I had some bad advice from a couple people.
    – drolex
    Sep 15, 2014 at 15:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.