crawlspace insulation


Old 04-23-03, 07:05 PM
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crawlspace insulation

I have a crawl space under my den approx 2 feet off dirt floor. Recently I noticed a very bad odor in the room. I opened up the boarded up crawlspace to find that there was insulation under the floorboards. I am pretty sure that the odor is from the old insulation. There is a plastic film covering the insulation (some torn). What is the best type of insulation to use on the floorboards?
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Old 04-24-03, 07:08 AM
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Cover dirt with plastic.

The dirt in the crawl space is the source of the moisture and it is the moisture that is causing the odor. Dirt even though it may appear to be dry, it does have moisture in it. Moisture in the ground evaporates into the atmosphere but when confined inside a crawl space, the moisture in the air gets absorbed by its surroundings. Example insulation and structual members inside the crawl space. Plastic over dirt prohibits the evaporation inside the crawl space and forces the moisture in the ground to evaporate outside the crawl space.

It is good to note that this actually lowers your energy bill and improves the comfort in the rooms above the crawl space. The reason for this is that it takes heat to cause evaporation. In other words, the evaporation inside the crawl space will extract heat from the ceiling above it. By prohibiting the evaporation inside the crawl space, it will not only reduce your energy costs but will improve the comfort in the rooms above. Much more so than the insulation in the floor will.

Unfortunately you are going to have to remove the insulation. The 2 reasons for this is the odor is probably a result of mold growth and the other is termite inspection. Once you solve the moisture problem, you have to make sure there isn't any damage. If there isn't any damage, I recommend insulating the ceiling of the crawl space.

As far as ventilating the crawl space, you will hear conflicting ideas. This is because there are 2 schools of thought. One argues that ventilating this area increases energy costs and the probability of moisture problems and the other argues that it reduces the probability of moisture problems and does not dispute the increased energy costs. My position of this issue is ventilating the crawl space. I base my position on the facts that insulation and vapor barriers do not stop heat or moisture flow, they slow it down. Which means there is a constant flow of heat and moisture into the crawl space during the heating months. And the other fact is Equilibrium Relative Humidity (ErH%). A process where air at a lower humidity level will extract humidity from other air and/or objects that possess a higher humidity level, until the humidity levels in the other air and/or objects are equal.
Old 04-24-03, 04:45 PM
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crawl way

And my 2 cents. What I have learned over 35 years. Had one way back, cant do it anymore. The heat just blowed down into the crawlway and had the registers cut in the floor around the home this worked like a big heat sink . Poly down and insulation all on the walls and sill plate no vents at all. There where 5 other homes like this but they had duct work on the furnace in the crawl way. When we started to check it out this home with the say open crawl way had the lowest fuel bills of all of the other homes. After that we have always put 6 mil poly on the ground over lap it 12" and tape it.Up the walls 12 ". A 2 " or 3" polystyrene on the walls up to the joist. Cut block like of R 19 F G and put this up in the joist space there on the sill plate all around the home.You could put a small heater and dehumidifier down there. You said opened up the boarded up crawl way???? When we have had a room or part of a home say on blocks. Like where the crawl way can be open all around we but a 6mil poly down on the the top of the floor joist then start the floor. put a R19 up in the joist space and a cheap ply on the bottom side of the joist. let the whole space under the room open. This way it works out just like the other walls in the home ED
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