Alaska Home Inspectors

John H Cooper · Home Inspector

Today as I was inspecting a house I came across a section of OSB sheathing covered with water resistant drywall. (see attachement). The seller indicated that they had problems the previous winter with icicles, and the builder had come back in and added ventilation and apparently this drywall? The only thing I can figure is that they thought it might insulate the bottom of the sheathing some? I couldn't see any deterioration of the sheathing in the immediate vicinity, and no evidence that they were trying to encapsulate something. Any ideas?

**Chris Roust** · Site Admin

I have never seen this in any of my inspections. I did send an email to a friend knowledgeable in building science and will post his reply when received.

I cannot imagine that this would solve any problems that existed in this attic. When you think of the uses of drywall and the possible problems in the attic, they do not seem to indicate that this is a good idea.

What are the dark areas at the edges? Are they construction adhesive?

**Chris Roust** · Site Admin

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I asked Marquam George, Assistant Professor and Department Head of Construction Technology, UAS, what he thought of the drywall in the attic.

Quote:

Chris: Is there some building science that would support this?
Would you recommend it be removed? I am not sure if it would be detrimental to the condition of the attic except that it may cause the sheathing to deteriorate if moisture were to get between them. The sheathing would not be able to dry.

Quote:

Marquam: I cannot think of one good reason drywall should be used in that application. I would go further that water resistant drywall is already an aberration.
Yes, I would definitely recommend that the drywall be removed. I do not believe it would ever be very dry, it could sure absorb a lot of moisture and then be left against the sheathing, very risky to be left there.

Marquam George has been the President of blu Spruce Construction and a General Contractor with Residential Endorsement since 1982. Marquam is a research committee chair for the Cold Climate Housing Research Center, a regional project manager for the Building America program in Alaska, and a committee member of ASHRAE 62.2, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings. He is a State of Alaska Energy Rater and has instructed for the Alaska Building Science Network, the Alaska Craftsman Home Program, and the American Lung Association of Alaska.

John H Cooper · Home Inspector

Ok, I got to the bottom of this one by calling the builder. This was an attached home... a "townhome." This wall was the common wall, with a valley between the two units. Basically two gable roofs with a horizontal valley in between. Not a very BRIGHT way to construct a roof in Alaska, but it makes for a more interesting roof line between two attached homes. They then installed inverted crickets on the front and rear to create two additional valleys to cover that one long horizontal valley.

The bottom line is, they installed fire resistant sheathing in the roof on both sides of the 2 hr rated wall so they would not have to install a parapet. However, the two units were not aligned with each other. This unit extended past the front wall of the other unit. The builder did not install fire resistant sheathing where the roof extended past the other unit. The city inspector decided that this did not meet the requirements of IRCR317.2.2.2 So, in accordance with the same section, the builder mitigated it with "one layer of 5/8-inch (15.9 mm) Type X gypsum board is installed directly beneath the roof decking or sheathing for a distance of 4 feet (1219 mm) on each side of the wall."

So, it is code. Not good code for an area with documented moisture issues in attics, and not even the way I would have interpreted the code, but I am not a code inspector. I did note in the picture that the adhesive looked red. Well it is. It is fire rated. As Marquam pointed out, it will probably be a moisture magnet. I already pointed that out to them. But it is a common wall between units. It extends PAST the other unit, but it is the common wall. [img][/img] Here is a picture of the outside of that corner. I presume that in the other unit, not inspected, I would find the same thing on the back of the house.

Carol Perkins · Home Inspector

You are right not a very good design for any where there is rain or snow.

I did know green board had a firerating. Could find any information that supported it use as a Type X product. What is the green stuff on the insulation and truss webs?

John H Cooper · Home Inspector

The picture was a little dark. When I used Photoshop Elements to lighten it up, the green reflection off the green board really showed up on the insulation and truss. It is just the reflection.