How to Repair a Roof Leak in a Valley – DIY Guide

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.

Three Types of Valley Flashing: Open, Closed, and Woven (also closed)

Open vs. closed valley flashing approaches
via Titan’s Roofing

There are three main types of valley flashing approaches:

  1. Open valley flashing approach that makes use of sheet metal flashing and is by far the most preferred and reliable type.
  2. Closed valley approach with the trimmed shingle edges on both sides of the valley. This approach doesn’t use sheet metal valley flashing, and hence is prone to failure.
  3. Woven shingles valley application with shingles from both sides of the valley overlapping with each other in a woven pattern. This approach doesn’t use sheet metal valley flashing, and hence is prone to failure.

All three valley flashing approaches use an Ice-and-water style membrane in the valley as a base level. Ice-and-Water shield is a waterproofing membrane that is applied directly to the roof deck, running from the peak of the valley (the point in which two roof slopes converge) to the gutter.

In this guide, we focus on the roof leaks that are due to closed and woven style valleys.

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.

Ice and Water shield rolls

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 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.

Installing roofing felt over ice and water shield in a valley

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 causes of the leaks whenever asphalt shingles are nailed way too close to the roof’s valleys (which can happen with both closed and woven valley shingling approaches). This stress can later result in premature wear and cracking of shingles, 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, 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, but only if the affected materials are replaced quickly.

WinterGuard Ice and Water Shield for Eaves and Valleys in Cold Climates

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.

Shingling a roof valley

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.

Temporary Repairs

As a temporary measure, you may be able to apply some roof sealant and roof cement to flash out the source of a leak if 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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2 thoughts on “How to Repair a Roof Leak in a Valley – DIY Guide”

  1. Last week, my roof started leaking because some snow and ice had accumulated in the valley of my roof. I inspected the shingles and found that the water shield was missing. I don’t think that one had ever been installed and so I am considering having a roofer come and install one. Would it be better for us to wait until spring to get the Ice and Water shield put on or is this something that we should have done immediately? If we were to wait until spring, then we would definitely need to rely on a temporary fix in the meantime.

    • Hi Faylin,

      So, not all roofs necessarily have to have the Ice-and-Water shield installed in the valleys and at the eaves of the roof deck. That said, the valley of the roof should at a minimum have 30 lbs felt/roof underlayment centered and installed before the shingles are installed. One of the best roofing underlyments in our view is DeckArmor, a breathable synthetic underlayment by GAF. It’s impenetrable to water and acts as if it were a roof underneath the roof.

      You see, asphalt shingles are not really a waterproof material, but rather they are a water shedding material, hence asphalt roofs must rely on slope for shedding away the rainwater, while ensuring a proper and unobstructed flow of water (unobstructed in the valley) to shed the rainwater away from the roof. That said, the underlayment underneath the shingles such as the Deck Armor from GAF we mentioned earlier, will catch any water that may seep through the shingles and let it run down the into the gutters.

      So, if the roof deck has neither the Ice and Water shield nor roofing felt/underlayment in place, then you absolutely positively must address that asap, or you could incur expensive water damage should the shingles fail to deflect the rainwater

      As far as the building codes are concerned, many northern states and places that experience significant snow and ice in winter, will require the installation of the Ice and Water shield or equivalent in the valleys and at the eaves of the roof deck (not over shingles), while the roofing felt or underlayment will need to be installed underneath the shingles whether or not the Ice and Water Shield is adhered to the roof deck.


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