Valley Roofs

Valley roofing result from two sloped panels of a roof that intersect at an angle which is lower than the subsequent portions of those roof panels. The intersection of where the two roof panels meet forms an inside angle and creates a valley or channel. Valley roofs can cause problems, especially when water and debris build up within the channel that connects the two roof sections. Proper construction and maintenance can prevent leaks and thus the need for repairs.

“The valley is the area along the connection of the roof panels and this area can be the single-most likely source of roof problems during the life of the roof. This is because debris can build up along the valley, making it harder for water to travel down along the channel and into the gutter system. When rain or ice build up along the valley, it can result in roof leaks.”

Basics Of Valley Roofing

Most homes have multiple roof lines due to varying architecture. This can be seen, for example, where the main part of a home’s roof meets the roof over the garage, which is a different height, or when there are varying heights or slopes of roofs that come together to add interest to a home’s roofline. When those roof lines come together and meet, they form a valley where they connect.

Valley Roofing Are More Prone To Leaks

Valley roofs account for a larger than average portion of all roof leaks. This is due to the fact that the valley, or channel, forms an area where water, ice and snow can naturally accumulate. If this water does not run down the channel and off to a gutter system correctly, it can penetrate the roofing material, resulting in a leak. Some of the reasons that can lead to leakage include:

Aging Or Deteriorating Shingles
As the roofing shingles begin to age, they can crack or pull up, exposing areas underneath that can allow water to penetrate. This is more likely to happen within the channel between adjoining roofs than along the flat surface of the roof.

Nail Locations
Proper nail placement is extremely important. If the nails are placed right in the middle of the channel or too close to it, standing water can start to seep into the nail hole or the nails can cause too much tension on the shingles, causing them to bend or break. Either way, leakage can result.

Improperly Installed Or Missing Flashing
It is important this roof type is properly installed roof flashing in order to provide added protection against leaks. This is usually a metal flashing that sits in the channel where the roofs connect to catch any water that penetrates through the shingles and to direct it down and off the roof. Some roofers in certain parts of the country may prefer to weave shingles together in the valley rather than installing flashing, but this is not a recommended practice. Flashing does a better job of preventing water penetration than woven shingles, which can warp, crack or split over time. Hemming the edges of the flashing will provide extra protection against any water seeping out along the edges of the flashing, rather than running down to the gutters.


Improperly Installed Shingles Over Flashing
When roofing shingles meet at the corner of the valley over the flashing, they must be properly installed. This requires the roofing shingles to be cut at the proper angle so they sit adjacent to one another from each plane of the roof, without causing an area where water and debris can collect. If the angles are not properly cut, leakage can result. Some roofers create a herringbone-like pattern of roofing shingles in the valley area.

Debris Build Up
If debris collects within the valley, it can deter water from flowing freely down the roof. If water is allowed to sit for a prolonged period because its path is blocked by debris, a leak can result. Built-up ice functions in a similar way. Another problem with a build-up of debris or ice is that it can slightly move, bend or break the shingles, leaving a vulnerable spot in the roof for water to penetrate.

Avoiding Leaks

The best way to avoid leaks is to make sure that all materials on the roof have been properly installed, including roof flashing and shingles. Ensure that nails have not been placed in any vulnerable locations. There are also moisture barriers that can be laid below any flashing or roof shingles to provide extra protection. Ice dams, gutter systems, etc. can be put in place and should be periodically checked to make sure they are working properly.

The roof should also be periodically inspected to make sure that there are no bent, warped, split, broken or loose shingles and that there is no build-up of debris sitting along the channel. With proper installation and periodic maintenance, these roofs should provide no problems and should last for many years.