A roof’s valley is very prone to leaks, especially if you have an older roof. The reason why the roof valley is such a vulnerable area of the roof has to do with all the rainwater and/or melting snow that accumulates and flows through the valley of the roof before draining into the gutters.
Roof leaks are also very common in the winter, when all the snow accumulating on a roof creates a potential for a leak to develop, especially if the roof’s valley on your home is not properly flashed and or if there is a substantial accumulation of melting and refreezing snow in and around the roof’s valley.
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There are many factors that can contribute towards a failure of a roof valley flashing; structural issues, inadequate construction, improper roofing methods, and the roofing material deterioration.
Common Causes of Roof Leaks in the Valley and How to Address Them
Missing Ice & Water Shield. A properly flashed roof valley should have an ice and water shield installed, with roofing felt being properly secured over the ice and water. If the ice and water shield is missing, then you will have to remove the shingles on both sides along the valley, put ice and water shield in place and re-shingle the roof.
You could check to see if the Ice-and-Water shield is installed by going into the attic and looking up through the spaces in between the boards of the roof deck to see whether there are any obvious holes in the valley, which would indicate that the Ice and Water shield may be missing. This may be a generally viable way of checking for leaks and assessing some of the damage, as long as you know what to look for, provided there are some spaces in between the boards comprising the roof deck where the valley is located.
Note that you will probably not be able to see much through the attic, especially if there are plywood boards installed over the roof deck (a large percentage of residential roofs will just have boards comprising the roof deck).
Here is a preferred method of checking: You can also put up a ladder towards the valley on the roof, lift up a few shingles and check to see if the ice and water is in place. If it is missing, then you will have to make sure it gets put in place.
If you have multiple leaking and failing valleys on the roof, then you may want to consider a complete re-roofing job, especially if the current roof is rather old, and will need to be replaced soon regardless.
Aging shingles in and around the roof’s valley can develop fissures and cracks that permit moisture to pass through. Intact shingles create a water shedding barrier in a new and/or a well-maintained older roof.
Exposure to the sun, wind, rain and snow can gradually cause asphalt shingles to dry out, shrink and break apart. Eventually the loose pieces of roofing shingles may actually get blown off or washed off the roof. When this happens, the underlying roofing materials get exposed, and an unwanted roof leakage become a very real possibility, and a potentially costly repair for the homeowners to deal with.
Improperly placed roofing nails during the roof valley shingling/installation can accelerate the shingle aging process. When roofing nails are placed within the seam areas of the roof’s valley, they can draw moisture through. Unwanted Tension in the roofing shingles can also be one of the cause of the leaks whenever asphalt shingles are nailed way too close to the roof’s valleys. This stress can later result in premature wear and cracking, causing speedy aging and failure of the roofing shingles. Roofing nails instead should be placed a minimum of six to ten inches away from the seam to reduce the pressure on the roofing materials.
Strong winds can sometimes lift up, damage, and even blow away some of the poorly installed asphalt shingles from the roof’s valley, particularly if the edges of the shingles are not nailed in place because of shingle strain, described above. Cut roof valleys also can easily be dislodged because of rain and wind. Damage to the roof and the interior of the house can be minimized or eliminated, as long as the affected materials are replaced quickly.
A roof’s valley can collect dirt, leaves, tree branches and limbs, snow and ice. The natural downward flow of water is interrupted when these foreign objects pile up in the valley, causing rainwater to pool and become trapped, ultimately seeping through underneath the shingles inside the house. To avoid this build-up, inspect your roof a minimum of two times per year. Removal of the debris accumulating in the valleys and gutters will allow rainwater to quickly drain away, thus protect shingles and flashing.
Pro Tip: Sometimes an older roof is more prone to leaks in the valleys because of the old repairs that didn’t fully resolve the underlying issues with the roof. The sealants and roof patching materials used in previous repairs, can crack and chip away over time. If your roof’s valley leak is an old repair gone bad, then consider having a professional repair the leak properly. Note that some of the surrounding shingles and flashing may need to be completely removed and replaced, but an otherwise “healthy” roof can be saved with a thorough quality repair.
As a temporary measure, you may be able to apply some roof sealant and roof cement to flash out the source of a leak provided that you can locate it, without removing all the shingles around the valley. It may be possible to do it, but it will likely be only a temporary measure that will work only for a short period of time. Eventually, you will need to remove all the old shingles from around the valley, install ice and water shield, underlayment, and properly re-shingle the roof.
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