I am reworking my roof on the front of my house. The previous roof had been leaking down the corner of the house where the garage and porch roofs come together. The previous roof had a sort of false roof added to create a plane moving away from the sidewall, although this seemed to move the problem down.

1. Roof Valley Before

Roof Valley Before

2. Roof Valley Before Showing Corner Damage

Roof Valley Before - Corner Damage


I have seen some references to low slope roofing membranes like these: http://www.gaf.com/Roofing/Residential/Products/Low_Slope_Membrane/Liberty, is this the way to go?

I just want to make sure water flows out of this area and over the corner without leaking as shown in the pictures.

3. Roof Valley Now enter image description here

  • You have to build that area up so there isn't a valley. There isn't a magic solution to put over it to keep water from coming in. I have done tar over metal sheathing. Fire the architect too.
    – DMoore
    Dec 3 '14 at 3:10
  • Agreed. Reconstruct the area so the inner corner is higher than the outside, so water runs out rather than accumulating. Flash the resulting drain path all the way from partway up all three walls down to and over the edge, then apply shingles "for pretty", minimizing how many holes you put through lower portions of the flashing and trying to ensure that any you must make are well sealed.
    – keshlam
    Dec 3 '14 at 5:00
  • And cover the whole area with rain shield material, the self sealing sheeting used under shingles and in valleys.
    – Michael Karas
    Dec 3 '14 at 6:47

Solution I ended up with:

enter image description here enter image description here

I extended the shingles well over the edge (not shown) and also added some kick out flashing (not shown) to further divert water away from the side wall and to the roof plane below. enter image description here


Ideally, you could use a pvc membrane and weld it all aover that place to make it fully watertight. Something like this: https://www.youtube.com/watch?v=AsJlBUmouw4

But it's likely that you do not have equipment or the PVC materials to do this. So I would go to Home Depot, and get a roll of GAF Deck Armor, and a tube of Quad Roof caulk.

Start from the very bottom, and work your way up with putting the membrane to the roof (at least 24" away from the wall, and at least 8" up the wall.

Fold around the codrners and overlap by at least 6" each side (12" total overlap). In the actual dead valley, fold it in, but do not make any cuts.

When you nail down shingels later, try to stay away from the wall at least 3-6" with nails.

This video may give you an idea of waht exactly I'm talkig about: https://www.youtube.com/watch?v=ZhrEMDFi28w

You can then put a piece of aluminum over the membrane in the very corner, just to hide Deck Armor from sun.

Also you can use EPDM rubber to seal there. You can get a small kit at rubberroofrepairkit .com - use 12" or wider membrane.

The most important thing is to overlap in the correct direction and let the water run off. Hope this helps. Good luck.

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