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Roofing And Valleys

Do you have any tips about valleys, when re-roofing a house? The information you have is great and the pictures are extraordinary. Thanks for already helping. We have heard that valleys should be flashed and then rolled roofing and finally shingles added. What is the best way to protect from leaks? 


I recently bought a book called "Roofing - The Best Of Fine Homebuilding", published by Taunton Press. I couldn't find any books on roofing at any stores so I ordered it online.

But I'm not sure I would recommend the book for you, because only one article is all that useful. The rest of the book discusses elaborate and unusual roofing techniques and materials.

The pertinent article describes 3 types of valley roofing methods: Closed Valley, Open Valley, and Woven Valley.

1. Closed valley: This is the method we used on our recent re-roofing job, which is what everybody has been doing lately around here, and because it looks neat and tidy. 

The shingles on one roof face run past the valley and extend up the other face for at least 12 inches. No nails are allowed within 6 inches of the centerline of the valley. That face of the roof can be done all the way up, and then a chalk line snapped to mark the centerline of the valley, which acts as a guide for cutting the shingles for the adjacent face.


The shingles from the other face run up to the valley and are cut along the chalk line. Again, no nails are allowed within 6 inches of the valley. When all the shingles were done, we ran a bead of roofing tar (which comes in convenient caulking tubes) under each cut shingle where it ended at the valley. This prevents water from getting under the shingles as it races down the other face towards the cut shingles.

Also, and this is CRUCIAL, we first applied a layer of Grace Ice and Water Shield to the valley (seen in first photo). This rubberized asphalt sheet is tricky to install (because it sticks to everything) but is GREAT because it seals around all the nails that penetrate it. In some cases it helps to install a length of metal flashing BEFORE the Ice and Water Shield, because the I&WS sticks REALLY WELL to metal, and sticks only "quite well" to wood.

2. Open Valley: This method has been preferred for many years but seems to be falling out of favor, perhaps because Ice and Water Shield has solved many of the problems that formerly were associated with the closed valley method. The open valley often starts with a layer of metal flashing along the valley, but that is not required necessarily. Then a layer of roll roofing is laid in the valley. This material comes in 36 inch wide rolls, and most people cut a strip about 10 feet long and then cut it length-wise to 18 inches wide. This strip is applied in the valley and nailed along the edges. End joints are overlapped 6 inches or more. Then chalk lines are snapped about 4 inches away from the centerline, on each side. These lines indicate where to trim the shingles when they reach the valley area.

3. The woven valley is done by alternately letting each row of shingles run past the valley. This requires that all the shingle rows line up correctly, which can be tricky.

It really takes a diagram to fully explain these concepts. If you are still in the planning stages, look at your local library for this book (or other books). Also, the Asphalt Roofing Manufacturers Association sells a book called the Residential Asphalt Roofing Manual, though I have not read this book.


Bruce W. Maki, Editor.



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Copyright 2001

Compiled October 25, 2001