Building Felt

[Danny]

Well probably a silly question here. Just inspected a house and the shake roof was shot. Had a lot of rot, moss and repairs. While in the attic it appears that they re-roofed and put felt paper under the shake? No sheathing, but it's my thought that the felt paper is not allowing the shake to dry thoroughly and causing premature failure. Any thoughts on this?

[mthomas1]

Generally, a good source for wood shingle/shake information:

http://www.cedarbureau.org

The felt is required:

http://tinyurl.com/2638c9

http://www.cedarbureau.org/installation ... -fig-4.gif

Spaced sheathing is recommended:

http://www.cedarbureau.org/faq/installation.htm

If installed over solid sheathing (not recommended by most manufacturers), best practice is to elevate the shakes above the sheathing on sleepers.

In the suburbs north of Chicago there are places where the shake roof of every other Cateau-To-Go is deteriorating before they are occupied because of improper installation.

[Danny]

Thanks for the info. Here in CA I hardly ever see that type of installation. Most roofers usually just do the spaced (lath) sheathing and then nail off the shake to that, leaving the shake visable in the attic area. Looks like some manufactures like to see the felt paper too though.

[carle3]

Danny,

Just an observation here. The installation you describe is for cedar shingles yet you call them shakes. A cedar shingle installation is usaully done on 1x4 roof boards spaced off about 3/4" to allow air to dry the shingle from the back side. If these are shingles and they have installed a felt underlayment then these will probably rot out from being wet the felt will restrict air flow to the back of the shingle keeping it wet. Now a shake roof is different in that it is usaully installed over plywood sheathing and with a double layer of felt. The shakes are not water proof so the felt is needed as an added layer of protection.

[Bill Kibbel]

Felt interlay is required for shakes, not shingles, by the IRC.

..it's my thought that the felt paper is not allowing the shake to dry thoroughly and causing premature failure

I agree. I've seen shake and shingle roofs documented to be 50-60 years old before replacement was needed. With felt, or on solid sheathing, it's a miracle if they'll last 15.

Now a shake roof is different in that it is usaully installed over plywood sheathing and with a double layer of felt.

The felt, cut in 18" strips, should be interlaced with each course.

The shakes are not water proof so the felt is needed as an added layer of protection.

I disagree. The felt, that is now required, is to prevent wind-driven snow from entering the attic.

[carle3]

quote:The shakes are not water proof so the felt is needed as an added layer of protection.

I disagree. The felt, that is now required, is to prevent wind-driven snow from entering the attic.

Bill,

I should have stated that this was a personal opinion and not a statement of fact. If wind driven snow can get through whats to stop the water.

[Kyle Kubs]

Just to add clarity for those who don't know. Wood/cedar Shingles & Shakes are two different things. Shingles are sawn with a perfectly flat surface, usually about a 1/2" at the thickest edge (vary's with quality level) Shakes are split not sawn. They split with the grain very often making them wavy and not at all flat and are usually quite a bit thicker. Bill, as usual, is right. Felt is only required with shakes as with the wavy, undulating surface they don't lay flat and wind can blow snow/water up under them - this also allows them to dry underneath. I would agree wind blown rain is also a problem, snow of course can blow a lot easier, but I think the point Bill was trying to make is that the felt is required not because the shakes aren't water proof, their less prone to water absorption then shingles which are sawn through the grain, but because of the open nature of the shakes that can allow wind to push rain/snow under them. Felt under wood shingles... Bad, way bad.[:-dunce]