The roofing company I hired finished applying Polyfresko bitumen on my garage, and instead of welding the beginning and end of new layers at the edges, they overlapped one layer over another by about 6 inches, resulting in a “hump” of overlapping layers.

Is this normal? I thought the membrane would be completely flat. First example:

enter image description here

The overlap can be seen from the driveway:

enter image description here

Where one sheet ends, they overlapped the new sheet by about 6 inches instead of welding at the edge of the sheet:

enter image description here


No, it’s not normal for the edges to be loose.

Poly glass is a self sealing modified bitumen roofing product. See here:


As you can see in Item #6 of the installation instructions, the seams are to be lapped 6” and side lapped 4”.

I think it’s installed correctly.

If there are loose edges you could have leaks, blow-off, etc. AND your warranty is void.

  • 1
    Op is not stating that the seams are loose. He is asking if the edge should overlap 6" verse edge against edge butt seams. I have no experience with the material under discussion, but I would guess that the overlaying makes a more water-tight seams. like installing shingles on a roof. Jun 13 '20 at 21:20
  • 1
    @Programmer66 Oops...you’re right. See changes in my answer.
    – Lee Sam
    Jun 13 '20 at 22:02

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