Insulating a crawlspace the Norwegian way
Reader unaware of potentially serious problemsBy Paul Bianchina, Friday, September 29, 2006.
Q: I'm originally from Norway and I've seen several Norwegian Web sites that say you should cover the underside of the insulation in your crawlspace with exterior-grade plywood. However, the American sites say to leave the bottom of the insulation open or to cover it with a non-tight covering. I tend to trust the Norwegian way of doing things because they have to deal with such crazy weather, but I want to make sure I'm not missing something here if I don't do it the "American" way. --Rune I.
A: Air will naturally move from a warm area to a cold area. The warm air in your house wants to move toward the colder crawlspace, and as it does it will take any moisture vapor it contains along with it. For that reason, when installing floor insulation, the paper or foil face of the insulation is installed facing up, against the underside of the subfloor, to create a vapor barrier that prevents most of that moisture from ever reaching the insulation.
However, that floor insulation vapor barrier still has gaps in it, so some moisture vapor will still get into the insulation. Having the insulation open below – facing the crawlspace – allows that moisture to escape. On the other hand, if you have added exterior-grade plywood below the insulation, which has several moisture-impermeable glue layers in it, you have now created a second vapor barrier below the insulation. Any moisture that gets into the insulation is now essentially trapped there, and if it builds up in sufficient quantities it can cause potentially serious structural and mold problems.
One last thing – when you insulate your floor, make sure that you add a vapor barrier over the ground, and that any water pipes in the crawlspace get insulated as well.
Q: I removed wallpaper from some of my bathroom walls, and it took of some of the paper face of the drywall. I've patched most of it with joint compound, but in some areas it still looks wavy. What is my next step? --Tom S.
A: Typically, if you have removed enough of the surface paper of the drywall to expose the gypsum core, the gypsum should be sealed first with a product such as Sherwin-Williams Drywall Conditioner – other manufacturers also make similar products –to prevent the porous gypsum from absorbing too much moisture from the drywall compound. I'm assuming that no sealer was applied, so that could be your problem here.
You mentioned that this is a bathroom. If the original drywall was waterproof – it will have a greenish-colored top paper and the inner core will appear more gray than white – and you have a number of areas where the paper was damaged, your best bet is to remove the drywall completely and install a new sheet or two.
If it was not a waterproof drywall and it is not in an area that gets a lot of moisture, you can try sanding off your patches and then applying a thin coat of all-purpose drywall compound. Let it dry, sand again and then skim coat the entire wall with the same material. Let it dry, sand smooth and then apply a sealer such as Sheetrock's "First Coat." Apply whatever texture you want, apply another coat of sealer, and then paint with satin or semi-gloss paint.
Q: About how long would it take a pro to install brick veneer on a 14 x 14 patio, and how long should a rookie expect to take if this is the first I've even done it? --Mike P.
A: It depends somewhat on the complexity of the design and the number of cuts required, but in general I would say that a pro could do the installation of the bricks in one to two days, with one additional day for grouting. The rookie has to deal with a lot of "head-scratching" as to layout, spacing and other installation details, as well as getting a feel for the use of the tools, so I would roughly double that time frame.
Remodeling and repair questions? E-mail Paul at email@example.com.
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