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Re-roofing - metal panels over wooden shakes

M

MikeC

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May 17, 2012
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240
Location
NW Pennsylvania
I am looking at IRC 2009 R907.4. As a firefighter, I am having a difficult time figuring out what is being accomplished here. Any fire in the attic will still expose the underside of the wood shakes to fire through any gaps in the old decking.

Can somebody help me understand reasoning of this R907.4?
 
The NY (modified) Residential Code 907.1 sends us to the back of the book, to Appendix J "Reroofing": (this section from the previous version):

AJ502.4.2 Recovering versus replacement. New roof coverings shall not be installed without first removing existing roof coverings where any of the following conditions occur:

1. Where the existing roof or roof covering is water-soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing.

2. Where the existing roof covering is wood shake, slate, clay, cement or asbestos-cement tile.

3. Where the existing roof has two or more applications of any type of roof covering.

Exceptions:

1. Complete and separate roofing systems, such as standing-seam metal roof systems, that are designed to transmit the roof loads directly to the building's structural system and that do not rely on existing roofs and roof coverings for support shall not require the removal of existing roof coverings.

2. Metal panel, metal shingle, and concrete and clay tile roof coverings shall be permitted to be installed over existing wood shake roofs when applied in accordance with Section AJ502.4.3.
 
The section is strangely worded.

My interpretation would be a metal roof installed above, but not in contact with, the wood shingle/shake.

Installation above creates an air space of "x" inches, thereby creating a concealed space containing combustible material.

Installing of the metal roof directly on, and in contact with, the existing wood shingle/shake, does not create a significant concealed area.

mj
 
New York has similar language to the code I am questioning.

NYS 2010:

J502.4.4 Roof recovering. Where the application of a new roof covering over wood shingle or shake roofs creates a combustible concealed space, the entire existing surface shall be covered with gypsum board, mineral fiber, or glass fiber securely fastened in place.
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What I am questioning is: 2009 IRC R907.3, exception #2:

Installation of metal panel, metal shingle and concrete and clay tile roof coverings over existing wood shake roofs shall be permitted when the application is in accordance with Section R907.4.
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R907.4: Roof recovering. Where the application of a new roof covering over wood shingle or shake roofs creates a combustible concealed space, the entire existing surface shall be covered with gypsum board, mineral fiber, glass fiber or other approved materials securely fastened in place.
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I am trying to figure out the intent of this section. Can anybody tell me what the commentary says?
 
Okay, I will tell the story that brought me here. A homeowner wants to replace a roof that has 2 layers of asphalt shingles and the original layer of wood shakes at the bottom. There are large gaps in the old sheeting and they don't want a mess in their attic. They have done their homework and are aware of R907.3 exception #2. They want to remove the asphalt shingles, place a ASTM E108 class "A" fire rated underlayment over the wood shakes and then install a metal panel roof over it.

I can't see where I can deny this, but I really don't understand it.
 
By the time they get the asphalt shingles off I suspest that most of the shakes are going to be broken and or torn up also. The 2 layers of asphalt shingles are both nailed directly to the shingles. This issue may solve itself.
 
Kaplagh said:
By the time they get the asphalt shingles off I suspest that most of the shakes are going to be broken and or torn up also. The 2 layers of asphalt shingles are both nailed directly to the shingles. This issue may solve itself.
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Good point and add to that a requirement for a flat substrate to secure the steel panels. Usually a 2"x4" lattice.

As for the mess in the attic. Tell them to cut a few big a*s holes and spread 10 mil Visqueen in the attic. 10'x10' squares that they can roll up and drag out of the attic.
 
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MikeC said:
I am looking at IRC 2009 R907.4. As a firefighter, I am having a difficult time figuring out what is being accomplished here. Any fire in the attic will still expose the underside of the banks outer roofing shakes to fire through any gaps in the old decking.

Can somebody help me understand reasoning of this R907.4?
Click to expand...

Hello,
Ideally a metal tile, shake or shingle roof should only be installed over one or, at most, two layers of existing roofing, and providing that the existing roof framing and decking is in good condition. A good way to determine "good condition" is to walk around on the roof you're considering covering to look for soft spots or evidence of weak, rotten, or compromised structural components. If there's any question about the integrity of such components, then removal should become an instant high priority. If the roof appears to be straight and solid, and there is no evidence of persistent leaks inside, then it's probably a good candidate for an over-top application.
 
You can also consider sistering additional Roof joists to the existing to improve stiffness on older framing.
 
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