"Understanding Your Home" by Building Inspector Mark Visser
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Valleys in split level homes. Usually the water from the upper roof valley is being discharged on the lower roof shingles and as a result this section of shingles is always worn out prematurely. When it was time to install aluminum soffits, fascia, eavestroughs, and downspouts on my 40 year old home I talked to the workers and asked them to make me two valley extensions. Once installed they redirected the water from the top roof valley to the top roof eavestrough. Also the downspout from the top roof was extended to the lower eavestrough. These two measures, valley and downspout extensions, are a real shingle saver!


Roof Flashing
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Flashings are pieces of roll roofing or metal that prevents water from entering the house. Flashing is required in the following areas:
- Around roof penetrations for vents, chimneys and dormers.
- Where two roof panes meet (valleys.)
- At the junction of flat roofs and walls.
Step flashings are rectangular or square pies of metal bent along the center at a 90 degree angle. They are used at the intersection of shingled roofs and walls, dormer walls or chimneys. One side is nailed to the roof, the other side is placed against the wall (no nailing) and covered by the wall finish or counter flashing.
Cant strips are rectangular shaped pieces of wood or pre-shaped metal that are installed on flat roofs along the outer edge of the roof and where flat roofs meet chimneys, adjacent masonry walls or parapet wall. For more information on parapet walls click here.
The cant strip is needed to avoid a right angle bend in the roofing. The roofing should be extended over the cant strip and at least 6" (150 mm) up the wall and capped with counter flashing.
Open valleys can be made of two layers of roll roofing or one layer of metal not less than 24" (600 mm) wide.
Valleys should be 4"-6" (100-150 mm) wide at the top and wider at the eaves where water runoff is the greatest.
Closed valleys can be flashed with one layer of metal, polyethylene or Type S roll roofing. Each course of shingles is continued across the valley.

Valley extension - a real shingle saver!
Personally, I don't think a closed valley or a valley made of roll roofing is such a good thing. Valleys handle a lot more water than the rest of the roof and water runoff speeds up the aging process. I have seen too many roofs where the roll roofing valley or shingles in the closed valley were completely worn out while the rest of the roof shingles were still in perfect condition.

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