Replies

1. 
   Malcolm_Taylor | May 09, 2021 06:06pm | #1

   Davin,

   My experience has been that even a fairly flat first layer ends up telegraphing through the new shingles. When you step back, what you are really doing is postponing work that will have to be done at some point. Pity the next guy in a couple of decades who finds out he is facing peeling off two layers.

   All that said, it's something that is done fairly regularly, and I can't think of a compelling building science reason against it.

1. Expert Member
   BILL WICHERS | May 10, 2021 07:44pm | #4

   The only technical reason I can think of against this is that it adds additional dead load to the roof, which can be an issue in areas prone to heavy snowfalls -- you're reducing the roof's available capacity to handle a heavy snow load without failure.

   I know of one houe that had a broken ridge beam due to too many shingle layers (it was something crazy like 5 layers). Remember how heavy all those shingles are. Aside from the weight, I can't think of any other technical issue with this.

   Bill

2. 
   user-723121 | May 09, 2021 07:02pm | #2

   I have found the roof over shingles to last about half as long as normal, 15 years vs 25 or 30 for a complete tear off and new roofing. I once did a roof that had 3 layers to be removed, the first layer being cedar shingles. 2 layers of shingles will not fare near as well with hail than will a single layer.

3. 
   Davin_ | May 10, 2021 10:30am | #3

   Thanks for the replies! Doesn’t seem like a layover is worth the savings.