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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?
Mary
We
recently bought a book called "Roofing - The Best Of Fine
Homebuilding", published by Taunton
Press. We couldn't find any books on roofing at any stores so we
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. |
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| 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. |
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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 seen this book.
Bruce W. Maki, Editor.
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