Crawl Space Insulation


Old 02-16-01, 06:36 AM
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My crawl space is directly below our main living area (kitchen, livingroom, etc..). This living area is the coldest in the house. I want to insulate the crawl space but cannot seem to get a feel for the right way to do it. The house is appr. 40yrs old and the crawl space is completely closed in and has a cement floor. There are currently 2 vents which are blocked by insulation. There are no signs of any moisture either past or present in the space. The walls are cement block covered by 1/2" black particle flake board like you would see behind aluminum siding. The above flooring has open joist some of which has piping and duct attached to the bottom of the joist. Should I insulate the joist or the walls. Given that there is no sign of moisture, do I need a vapor retardent? If I do insulate the joist, how should I deal with the ducts and pipes as they are secured to the bottom of the joist. Was splitting the atom this confusing?

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Old 09-03-01, 04:06 PM
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Just came across this post and realized it's very similar to my situation. Anyone have any suggestions. RawRookie - what did you end up doing?
Old 09-05-01, 08:30 AM
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Several years ago I drveloped a system that performs superior to anything I had encountered.

You probably have FG between the joist at the ribbon board. Remove this as it is practically useless and can cause your rim board to rot out.
This system does not require vents, so SEAL those.
Even if you do not see signs of WATER you still have moisture from the ground.

Install 2 layers of 4 mill plastic(crossed) over the gound with a 6" overlap of the seams. ONE layer going up the side wall and attached to the side of the top plate.

Install a 48" wide radiant barrierr (RB) around the perimeter, again, attached to the side of the top plate and let it hang down to the vapor barrier. Do not trim if the wall is shorter than 48", just pull the bottom edge towards the center to reduce the floor space area. The RB to use should be a plastic film with foil both sides. A paper base product is OK, the plastioc is easier to work with.

Cut RB pcs that are slightly larger than the space between the joists. Install them at te rim board, but, not on the rim board. Leave an air space.

Although I have not done a crawl space with a concrete floor the results will be the same as a wood floor, unless the floor edge is not insulated to the outside. And that could affect the results regardless of what you do.

The results are that you will not have to worry about frozen pipes. The crawl space temperature should be within 5 degrees of the upstairs. If you have had mildew in the rugs, that should go away. Because of the floor mass you might have to put a RB over the plastic to further warm up the concrete. This has never been required with a wood floor.

Thank you for considering my personal opinion. If you have any further questions or material scource problems, let me know.

In your search engine, enter: "radiant barrier insulation" or reflective insulations".

By the way I'm in the St. louis area and it gets cold here too. And yes this is much better tan foam.

Old 09-09-01, 09:00 AM
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good question

I too am having problems figuring the best way to procced in this situation. I just read that after putting down a vapor barrier, you should run batts down the walls and about 2 feet on to the floor all the way around. This apparently provides you with a envelope of air in the crawlspace to insulate the floor above. Unfortunatly, I'm not clear on which way the vapor barrier on the batts should be. Normally toward the heated part, but here there will already be the plastic against one side. Anyway, hope this helps and hope this encourages a more knowedgeable response.
Old 09-09-01, 03:53 PM
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I hear you. I've been doing research on this for several weeks now and there seems to be no one right way to do it. I've called several contractors and here's what they said:

Contractor # 1 - Wants to blow sticky Cellulose along the band joist and down the wall. He will block the vents up as well. $ 550.00

Contractor # 2 - Wants to blow Rock Wool in (with glue) and will put fiberglass in the vents so that I can pull it out if I ever need to vent it. $650.00

Contractor # 3 - foam rigid board along walls and nothing else. $225.00

Contractor # 4 - Attach fiberglass to band joits and let it roll down the wall onto the floor two feet. $250.00

I do have a 8 mil vapor barrier covered with several inches of concrete. I think I'm going with option # 4 but doing it myself. This weekend I went around with the foam in a can and sealed up holes where the water pipes go up. I also purchased a de-humidfier for down there (hopefully it won't get much use). I started buying the batts of unfaced R 19 today. Once the walls are done, I'm going to hang tight and see how it goes this winter. If the floors feel cold and if the crawl seems cold, I'll also do the floors (crawl ceiling) with paper vapor barrier up, toward the heated side. But hopefully it won't even come to that.

Old 09-10-01, 07:11 AM
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I hate to tell you but fiberglass and celulose will suck up moisture like wouldn't believe. Once that moisture is in there you have little or no insulation values. Also, with ffiberglass you can almost gaurantee mildew or mold problems. I'm an insulation contractor and the guy that has to go in and correct the mess these products have created.
Also these products can rot out the rim boards due to holding the moisture against the wood. If you live in a cold enough climate then your pipes are also subject to freezing. The radiant barrier is the only way to go.
Good luck
Old 09-10-01, 08:09 AM
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I can see you're a big fan of radiant barriers, but wouldn't encapsulated fiberglass take care of the problems you mention? Also, it seems ot me either rb or regular insulation will help keep the pipes from freezing. Based on the rb I've seen at Home Dpot (if we are talking about the same stuff) I don't think I could install it well enough to be as effective as batts. My cellar walls are stone and very uneven.
Old 09-11-01, 04:27 PM
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You might say that I'm a big fan. I have been designing, selling and installing radiant barriers for 29 years. The method I described to you is the result of trying to design a system that wuld be super efficient and cost effective, plus, an easy DIY. You would see how many fiberglass disasters I've had to correct over the years.

The fiber glass will suckup moisture period. That's the nature of the beast. If you want real technical data, get hold of the ASHRE reports. The plastic is a marketing ploy to reduce the itch so that there will be less customer resistance. It's still carcenogenic, has carcenogenic chemicals in it and allows deadly mold spores to attach to it.

Go to the Heating & cooling section of DIY and check "crystal 170" if you want to see how bad it can really get.

You let the material "hang", so it doesn't matter what type of walls you have. This is actually easier to install than fiberglass. Remember, this material doesn't condensate moisture, and with with the double plastic you should not have a high humidity in the crawl space. Therefore no mildew in the rugs. I don't think a Fiberglass would put in writing that fiberglass wouldn't create such a condition.

The first house I installed this method was in an extremely cold February about 10 years ago. The plumbers went into the crawl space to finish up. No heat in the house, temp in the low teens. They took their 500watt lite down to see with. In 5 minutes they were peeling clothes. Do that with fiber glass.

If you think you need more detailed info contact me at [email protected]

Thank you for considering my personal opinion.
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