I'm planning on reroofing my house myself. The house is a ranch home in SE Michigan, 4 x 12 pitch, and has four valleys. I've already decided on a tear-off and using dimensional shake shingles and ice & water shield at the eaves and valleys. My question is, should I go with the California cut or open valleys flashed with aluminum? Which is better?

Or perhaps I could flash under the California cut?

ALL the reroofs in our suburban neighborhood have the California cut with dimensional shake, but I heard (from this site) that open valleys flashed with aluminum are more robust because they are more resistant to the wash and abrasion from the weather. Since I'm doing it myself on my own home, and I'm not trying to beat the 'flat rate', I'm looking to do it the best way possible.

 

Id have a sheet metal shop break up some valley for me. We do it all the time for the roofers here. We make what is called a storm valley. Its made out of 24"X 96" so it ends up in 8 ft long . It look like a W. the center line is up about a 1/2" and both edges are bend over 160o. That way you have two valleys like for the water to run down . Also that center dont let the water run over and under the shingles on the other side of the valley.

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I am not a roofer,but in talking to a rep from a large roffing contractor about putting metal under my valleys he said don't do it as the metal soaks up heat and cooks the asphalt. The expose metal sounds good to me. Tom

 

"... metal soaks up heat and cooks the asphalt."

I happen to be a materials engineer. The above statement doesn't make sense. If a metal valley is not exposed to the sun, it can't really soak up heat from the sun. The best it can do is transfer the heat further below... but no more than if the metal layer was not there in the first place.

If it was exposed to the sun, I believe metal - such as shiny aluminum - would reflect more heat than would a shingle.

What I'm really after is a robust valley for my conditions. Since valleys are prone to be the first to give a problem with age, I'd like to delay any problems.

 

Then get a 26 ga storm valley made up for you job. You hold the valley down with clips on the side and just over lap the 8 ft about 6". That way it can all move for expansion. Go copper or galvanize.