Roof Valley

What would write about this roof valley?


Closed cut valley using laminated shingles. Shingles are cut 2" off the centerline of the valley.
Looks ok to me. :slight_smile:

Yup, the installation of this closed-cut valley looks very good.


90% of these valleys will leak when this roof gets older…old school way of roofing out here in CA we call that a california valley.

Brian, there is a distinct difference between our conventional closed-cut valey and the alternate closed cut valley called the “California Valley”

CertainTeed highly recommends the conventional one over the other and the 3-tab should not be used with the California cut valley.


true, however in my 15,000+ roof inspections over the last 10 years I have seen both styles leak…I always use valley metal on our new roofs and weave my felt underlayment!

I’ve seen the closed-cut done two ways… overlapped by two inches +/- and held back 2"+/-… the tech document Marcel refers to appears to say to cut it back 2" vs. overlapped… which is technically correct?

The steeper or higher roof should run through onto the opposing slope.

In “California” valleys, shingles are not cut at the valley. Instead, shingles on the first slope are run through onto the adjacent slope. On the second slope, a single row of shingles is then installed vertically up the valley parallel to the valley centerline with the cutaways facing way from the valley centerline and each shingle course is started at the valley and cut off at the rake.

You can identify them by spotting the bottom of the lowest shingle (in the row run parallel to the centerline) at the base of the valley. It forms a small triangle that doesn’t match anything else in that area.

As Brian says, it’s always a good idea to use valley metal. As Marcel says, CertainTeed does not recommend the California method, but many, many are installed because they cost less to install when the installer is not very skilled.
When work is slow, they hire less skilled peope in an attempt to stay profitable. When there’s lots of work, they hire less skilled labor because they have trouble finding enough help.

Ken, should a conventional closed cut valley be overlapped by 2", in the middle of the valley or cut back 2"… I see it all three ways, I though cut back 2" was the correct method.

Lapped shingle drainage valleys are suseptible to leakages over time, and will not last as long as other roof shingle areas. Installations of metal valleys would be more appropriate, and would last much longer. Suggest monitor roof drainage lapped valleys seasonally. Replace if deterioration is noted.

I see many lapped valleys leak here in KC all the time after about 8 years of comp roof age. Many are standard comp, and leak at joints. Cut joints will leak at some point, and lapped will age quicker than metal and other flat shingles.

Jeff, the proper method is like shown in this detail for conventional cut-valleys.

The logic behind it is to keep the water shedding down the valley as much as possible and not running along the cut edge and underneath those shingles.
The top 2" of the shingles are diagonally cut to help divert the water.
That is if it is done right.
Therefore, if you pick up the shingles, you should be able too see if done right. :slight_smile:

Marcel I wasa taught to never seal uner a valley but to cut the tips on the cut side to stop water following back under the shingles. If that makes sense. It does work well.

You are correct Curtis, I misspoke confusing myself with the California valley and the alternate closed cut valley where in that detail it is required.
The closed Valley application per CertainTeed does not call for sealant and requires the cut 2" diagonal off upper corner of trimmed shingle.

Thanks for correcting me.
I edited my post above to make the correction.:slight_smile: