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I'm considering buying a house, but in the crawl space, they installed the insulation like you would from the inside -- by stapling it in using the kraft paper.

Of course this means that there is exposed kraft paper (fire hazard?), and likely no vapor barrier.

Would it be worth flipping the insulation so it's installed correctly? If the only issue is the vapor barrier being a fire hazard, should I just peel that off and install wires to hold it up?

And in case it's a factor, the area can get quite cold in the winter -- it's on a mountain at 1700 feet (~520m) above sea level. It's in Virginia, if that would affect any codes regarding insulation.

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Nearly all of Virginia is considered to be in the "mixed-humid" zone. On an annual average, moisture migration is fairly evenly distributed (alternating toward the interior and toward the exterior).

Moist air tends to migrate toward the cold side of a wall. The vapor retarder is installed correctly, in your crawl space, to discourage exterior humidity from migrating toward the interior, during the Summer, especially if air-conditioning is used.

By maintaining space between the un-faced side of the batt insulation and the ceiling drywall (R-19 in a 2x8 stud bay with faced-side stapled to top of Floor Joists [FJ's]), an air channel was created to facilitate drying (of sorts) via the wood FJs.

In areas (climates) that have a distinct Summer vs Winter there is a good chance (depending on humidity, the use of air-conditioning, and moisture permeability of the structure's siding material) that the air retarder of batt insulation will be on the "wrong" side of the building's heating/cooling envelope half the time.

One reason why old (19th Century U.S.) homes don't suffer from moisture damage, mold, mildew in the exterior wall cavities (unless caused by some drainage or structural failure) is that the wall cavities either had no insulation or the insulation (sawdust, newspapers, sheep's wool, etc.) permitted fairly quick drying of the wall cavity.

  • Thanks. That makes a lot of sense, now that you've explained it. – Joe Feb 1 '17 at 20:07
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Kraft paper is a vapor barrier (or more accurately a retarder), and in my opinion it's no more a fire hazard than the lumber it's stapled to and all the stuff you have in your home. Inspectors sometimes call it out to justify their existence, and buyers sometimes use it as price leverage, but it's not a real concern. I'd leave it alone unless you have better reasons to change it.

You don't say what R-value the insulation has, but chances are it's adequate for a floor in your climate zone.

With the insulation upside down the kraft paper is not working as it is intended. Moisture from inside the house can now accumulate in the insulation which will drastically reduce the "R" value.

  • R-19, installed into 2x8s ... It's stapled into the side of the joists, so it might be compressed if it requires a full 7.5". (I know it's compressed around the plumbing ... but I didn't think to take an IR camera with me when inspecting. (just after freezing rain, so it would've been really obvious if it was leaking heat)) – Joe Feb 1 '17 at 18:55
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    FYI, R19 is usually installed in 2x6 walls, so it takes 5-1/2". – isherwood Feb 1 '17 at 19:15

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