drywall vs OSB

[big e lewis]

New polebarn, I will be putting in insulation in roof and walls for inside heating for Michigan winters. Surprisingly, the cost is about the same for either locally. I would prefer OSB on the walls, to make it easier to build shelves, ect onto. Is this a problem, or is there a reason to use drywall? Thanks, Earl

[Mike Dobony]

Fire resistance and vapor barrier fiberglass requires a fire resistance covering (drywall) per code and manufacturers instructions.

[marson]

messagenews: [e-mail]...

If it attached to your house, then you will need a one hour separation which would require drywall. For a freestanding polebuilding, I know of no code that requires you to drywall it.

[Cindy Hamilton]

We're in Michigan, and we used OSB instead of drywall in our fully detached "garage" (which is in use as a woodshop for my husband). We had a variety of reasons, including giving the space more character, having somewhat greater resistance to damage, and being able to get by without mudding. We have a good relationship with the building inspector, and we talked it over with him before buying the OSB.

You'll still want to hang your shelves from the studs, I should think, so the OSB and drywall are similar from that perspective.

Cindy Hamilton

[Mike Dobony]

What about insurance companies dropping coverage for not following manufacturer's instructions?

[marson]

What manufacturer's instructions are you talking about?

[trader4]

Yes, good question. I was wondering what manufacturer he was talking about too.

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[Mike Dobony]

Read the vapor barrier on fiberglass insulation. It requires flame retardant covering.

[marson]

I haven't used kraft faced fiberglass in years and years.

[Robert Allison]

Me either. It is against code to use it here if you have housewrap on the exterior.

[Mike Dobony]

So what type of facing do you use? Foil? Plastic? None?

[Mike Dobony]

The houses here have both kraft faced insulation and house wrap.

[Robert Allison]

You are then creating a pocket of space that will store moisture and therefore create the perfect environment for mold and decay. It is against code to encapsulate a wall that way here. It could be a regional thing, I don't know.

If you MUST use faced insulation in this area, then you MUST cut slices in the paper to ventilate the secondary vapor barrier.

I will give you an excerpt from this site:

In mixed climates (not fitting either of the above definitions), the vapor retarder should be placed to protect against the more serious condensation condition, summer or winter. If in a mixed climate the winter indoor relative humidity is kept below 35 percent, a vapor retarder at the interior side of the insulation is usually not required, and an exterior vapor retarder strategy is most effective. Where winter interior humidity is not controlled or if a humidifier is used, an interior vapor retarder is most useful. Vapor retarders should never be placed on both sides of a wall. Where a vapor retarder is employed, the opposite wall surface must provide a permeable surface to allow drying to occur. Thus, in hot, humid, cooling climates, where a vapor retarder is employed at the exterior, the interior wall surfaces should be permeable. No vapor retarder paints, kraft-faced insulation, or vinyl wall coverings should be used. Conversely, in northern heating climates, with interior vapor retarders, the exterior wall coverings should be vapor permeable.

[marson]

And in cold climates, we use 6 mil poly, caulked to the floor plywood, with all electrical outlets and attic bypasses etc caulked and sealed. Seams taped or caulked. This is required by code. Our local inspectors would never let kraft paper pass in any case. As Robert says, the exterior is covered with felt or building paper.

Regarding the OSB in lieu of drywall, I'll point out that OSB can be used as a thermal barrier covering foam insulation in a heated crawlspace. I suspect that codes would allow it in a detached shop, though I am no code expert.

[Wayne Whitney]

I thought house wrap is supposed to be vapor permeable while keeping out liquid water?

Cheers, Wayne

[Robert Allison]

It is supposed to be. However, in the instance of the south, our building codes consider it to be a vapor retardant and don't allow the use of an interior and exterior vapor retardant. If you use felt on the exterior, then you can use faced insulation here. If you use Tyvek, you cannot have a faced insulation on the interior.

Believe me when I tell you that I have been red tagged for faced insulation with housewrap. All I had to do was cut the paper to get a pass on the insulation inspection (energy inspection).