Insulation above crawl space (dirt mound)

Old 04-13-04, 10:28 AM
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Insulation above crawl space (dirt mound)

Hello, all. First time poster.

A first floor corner bedroom (location new york suburb) is very cold in the winter and I notice the crawl space below in the basement is a possible source, despite closed foundation vents in the winter.

I would like to install fiberglass insulation between the exposed basement joists below as one approach to helping fight the winter cold. I am looking at R-19.

I have two questions: whether to moisture barrier the mound, and which side the paper should face on the insulation.

#1. In the summer the mound is rather damp due to seepage from the surrounding area. My concern is humidity build up in the insulation. I understand that covering the mound with 6mil plastic is recommended, but someone in a (brand) home improvement store recommended *against* that as it might be a collection point for mildew. Is that true?

#2. Re Paper facing on the insulation. From all the postings I see, it says the paper faces the "living" space, but this is an unfinished, unheated crawl space. The manufacturer says that the paper side needed to face UP toward the floor above. I am now very confused. Another source I read said the Kraft can face down, if you "slash" it to allow it to breathe.

If possible I think having the paper down makes sense so there is not exposed fibers in the area, and seems like installation would be easier since I can staple the paper to the sides of the joist rather than having to use the metal supporting spines.

Thanks in advance for your help,
robbie g.
Old 04-13-04, 04:16 PM
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Moisture barrier over dirt will make the room above this warmer in winter. The reason for this is the same reason why you feel cooler after taking a shower in the summer. The moisture on your skin evaporates and it uses your body heat to create the evaporation (Gas Law), thereby lowering your body temperature and you feel cooler. This same principle applies to your dirt floor in the crawl space. The moisture in the dirt evaporates and to do so it extracts heat from the room above to create the evaporation. The moisture barrier over the dirt prohibits the evaporation, hence the room above the crawl space will be warmer during the winter. Solar pool covers do the same thing, it prohibits evaporation, hence the pool water stays warmer during the summer.

Mold and mildew is a concern with moisture barriers in crawl spaces. The way to avoid this from occurring is to tape the seams, if any, and attach the moisture barrier to the walls of the crawl space, at least six inches up the walls. What this basically does is prohibit air from getting underneath the moisture barrier. Because it is the air that carries the spores for the mold and mildew to grow.

The vapor barrier on the insulation faces up. The way to install it is to use joist hangers. They look like the wire used for clothes hangers and they have sharp ends. You can purchase them at any home improvement or hardware store. The way to install the insulation is to push the insulation between the joists with the vapor barrier facing upwards. Then take a joist hanger and push it between the joists to where it will hold the insulation and push the sharp ends into the joists. Install a joist hanger every 3 feet. This is actually easier and faster than stapling insulation between the joists.
Old 04-13-04, 05:32 PM
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Thanks for the great and quick reply.
Old 04-14-04, 07:03 AM
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With resercon most of the way 6 mil poly on the ground.only we like to put the insulation on the walls and just up there in the joist space on the sill plate all around the home. not in all the joist.


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