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    © Mark Saville 2006  

How to Do Roof Valleys


Most roof valleys you see as you drive down the street will be the old exposed metal flashing type for reasons which we're not really sure of but that method did nothing but cause water backup because of the freeze thaw process in colder climates with a lot of snow. In warmer areas with high winds and lots of rain, water can actually be blown up under the shingles if there was no sealant applied.



Use a rubber membrane in the valley under the shingles instead of metal flashing and then install the shingles to match the photo below. This creates even heating in colder climates with snow while the exposed metal keeps melting and causing ice buildup when the sun hits it.

roofing valley

The image to the left is an example of how a valley should be done. You continue one side of the valley shingles up a couple of feet past the other side of the valley and then bring the other side over and cut them off in a nice straight line. This creates a much better look as well as a leak-proof valley. With the rubber membrane under the shingles as added protection if any water did manage to get in there which is highly doubtful, it would just drain out into the eaves trough.






Where the ridge intersects the other roof the roofing shingles must cover over the lower roof so make sure you install the shingles on the lower roof first. This way the overlap is the proper way and any water from the higher roof will be drained out of the valley. The ridge cap on the lower roof can also go under the overlap on the upper roof.



Roof Valley Intersection
This makes a nice neat job where the valleys intersect.

A roof is there to keep water out so that should be the first concern. It's a fairly simple job to install asphalt shingles in a straight line but when it comes to valleys, chimneys and installing step flashing you need to know how to do this properly. Never rely on caulking where there should be a flashing. Everything you do on a roof should stick to the basic method that shingles use to keep water out of your house. Shingles are overlapped so the water drains off of one and onto the next one below it. This process continues until the water reaches the edge of the roof. Never create a spot for the water to pool because this is where you get leaks and leaks mean costly repair.



© Mark Saville 2006 Reprint with Permission only.

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