Closed Cut Valleys
Closed cut valleys start with a row of ice shield installed through the center to serve as a water proof liner. The “gasket” effect of the ice shield sealing around any and all nail holes that puncture the membrane is effectively the last line of defence in your valley. This liner is very important for maintaining a trouble free valley. Shingles are then installed on the lower slope (or the slope with the lowest water volume rate). These shingles will overlap the valley. Next, shingles are installed on the higher slope through the valley center. Finally, the shingles on the higher slope are cut by following a chalk line 2” off center.
Open Metal Valleys
For the same reasons closed cut valleys use ice shield, open metal valleys also start with a row of ice and water shield serving as a water proof liner. Next, a prefabricated metal valley flashing is installed over the liner. (There are several options for flashing metal. Logik Roofing recommends and uses a pre-painted 26 ga steel for valley material. Thinner steel or inferior metals can compromise the quality of the valley system.) Finally, shingles are installed over the valley flashings with the center line remaining uncovered by shingles. The exposed metal should gradually widen to handle the increased volume of water at the lower parts of the roof.
Pros And Cons For Each
Each system has its own advantages and disadvantages. Some of the more industry agreed pros for closed valleys are:
Aesthetically pleasing final product, quicker install and typically more cost effective price, acceptable by most manufacturers.
The cons include:
Higher fail rates in Ontario, requires more skill and attention to detail despite quicker install time, technique seems to fail before the rest of the entire roof assembly.
The advantages of the Open Valleys include:
Less skill required to make a leak free system, longer life span, able to handle heavy rain and snow on roofs between 3/12 and 6/12
The disadvantages often include:
Higher cost due to material cost and install time, some consider these systems less attractive from the ground, not always the best choice when the two converging roof planes have very different roof pitches.
So which one is actually better?
The debate on this topic has been going on for years, not only between contractors, but even between shingle manufacturers. The manufacturers that Logik Roofing prefers will accept both techniques without compromise to your shingle warranty. However, we do have our preferred method. From our experience, open metal valleys seem to perform better for 2 main reasons:
- With less friction on steel than on a shingle, snow, ice and heavy rain will shed quicker out of an open metal valley, leaving less chance of a leak. This is particularly important on lower sloped roofs (6/12 and less)
- Metal seems more durable than shingles in a valley. The abuse a valley faces from collecting water off of two converging roof planes and lingering snow causes the shingle granules of a closed cut valley to debond prematurely. This causes the shingles to wear quicker in valleys. The result is a beat up and withered looking valley near the end of the roof’s life, while the rest of the roof looks much better. Open metal valleys, however, seem to stay in much better condition over the roof’s life span.
In closing, I think it’s important to note that both techniques require an experienced and trained installer to ensure the valleys will perform adequately over the roof’s lifespan. If the installer is not trained to know things like a closed cut valley must be cut two inches off center to work properly, or that an open metal valley cannot have shingles coming into the valley that are cut to a point (they must be chamfered), then problems will most likely ensue.
If you have any questions on valleys or any other aspect of your roof assembly, please contact our office.