Best low slope valley construction

I have an addition which will have a valley with about 1/12 pitch, Asphalt shingles. I’m thinking butyl membrane under the shingles, 18in up each side.

Just slap peel and stick in valley ,cheap,ez,lasting.

Anything that flat requires flat roofing material, not shingles. You’re asking for trouble trying to make shingles work even with membranes and tapes underneath.


The main house is 5/12 pitch. The addition is 3/12 or better. The valley is about 1/12. What do I do at the valley. Also I could do the whole addition, not large - 12x12, in EPDM or something but want it to look halfway decent.

Shingles are not an option. You could put three layers of epdm and the first nail you put through compromises it.


You can get modified bitumen products that will have granules and match the shingles.

I’d recommend seeking out a roofer experienced with torchdown.

There are self adhered modified products available but these are very expensive and vastly inferior to torch applied systems.


Oops, My valley slope is 2/12, not 1/12. That helps, probably doesnt change a lot.

Something does not add up, a 5/12 meeting a 3/12 will not result in a lesser pitched valley. Do you have any pictures?

I think he is referring to a low slope valley, sometimes called a ‘Hog’ or ‘Trough’ valley.

Had trouble with my computer, but here is a drawing, attached.

Thinking of reducing the addition from 13ft square to 10ft. That would help a little.