Conflicting theories about crawl space vents

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  #1  
Old 11-10-01, 01:56 AM
techtim
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Question

I'm in the process of insulating my family room crawl space. I am putting in R19 designed for floor joists. However, this crawl space (rest of the house has a full basement) has 2 outdoor vents and a heating duct with an adjustable damper. It's a 32 year old house.

I've read in the posts that my crawl space under my family room should ALWAYS be vented, winter and summer (Iowa winters!). What is the purpose of the heating duct? It would obiously be useless if I didn't close the vents for the winter.

Am I mistaken, or should I really seal the vents for the winter and open the heat outlet? There are no water pipes or drains in the crawl space. And if I should open the heating duct, am I wasting money on unnecessary floor insulation?

Thanks for any help, Tim
 
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Old 11-10-01, 05:28 AM
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Cool

Close the crawlspace vents for the winter, keep the heating duct closed (I assume that your family room is heated otherwise), and insulate the floor with the vapor barrier up toward the heated space.
It should save you money.
Good Luck!
Mike

 
  #3  
Old 11-11-01, 05:40 AM
T
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Vapor retarder in crawl space

And, don't forget to cover the soil in your crawl space with at least a 6 mil polypropylene (plastic) vapor retarder.
 
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Old 11-11-01, 06:50 AM
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The "R" in R-19 stands for resistence and the "SP" in SP-15 which is found on insulation with vapor barriers stand for static pressure. The "R" explicitly implies that it prohibits heat from going through but does not stop it. The SP-15 is a rating for the performance of vapor barriers, this rating indicates that the moisture content of the heat would be reduced to 15%. The purpose of this is when the heat and moisture goes through the insulation, at one point the temperature of the heat will reach dew point. Since the moisture content of the heat was reduced to 15%, there is insignificant amount of moisture in the heat to condense. As the heat and moisture gets into the crawl space the vents dissipate it. If you close the vents, the heat and moisture will not dissipate and you'll have a moisture problem. If you would like to know more about this , click on the little red house icon at the bottom of this page and read topic "Ventilation".
 
  #5  
Old 11-12-01, 04:07 PM
rbisys
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Greetings,

If you install fiberglass in a crawl space you are sure to get condensation. That is the nature of the beast. Moisture can reduce the insulation value up to 50% or more.
The moisture also means that you can grow mold/mildew on the FG and that can get into the rest of the house.

The way I insulate crawl spaces so that they are warm with no moisture problems is to attach a 4 mil plastic sheet to the side of the top plate and allow it to hang down to the ground and across the ground. Install two sheets on the ground cross and over lapping. Install a radiant barrier (48" wide) to the side of the top plate and let it hang down. With this system and a WELL DRAINED floor, you can seal off the vents. You will also want to remove the FG from between the joists at the rim board and replace with radiant barrier material. This will prevent any moisture from forming. FG is noted for rotting out rim boards, and joists.

The crawl space area temp should be within a couple of degrees of the upstairs. If you have particularly cold winters you may want put an additional radiant barrier over the plastic on the ground.

For more radiant energy barrier info, enter your search engine "radaint barrier" or "reflective insulation".

Thank you for considering my opinion.

 
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Old 11-14-01, 03:32 AM
Larryz
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Twelvepole I have a ?

Why would anyone want to put poly in the crawlspace? I live in California, and I don't have anything on the ground in mine. What is the benefit of doing this, other than making it easy to slide around under the house, ?
 
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Old 11-14-01, 03:49 AM
T
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Moisture retarder

Covering the soil in a crawl space with polyethylene tends to retard the amount of moisture that rises out of the soil and into your home. The covering is frequently referred to as a vapor barrier. The installation of the protective covering is very important in the installation of hardwood flooring over crawl spaces as hardwood flooring is kiln dried to a very low moisture level. Even with proper accilimation of the wood flooring to the temperature and humidity of the home before installation, the moisture and humidity from the crawl space area and causes such problems as cupping of hardwood flooring. Thus, the amount of moisture rising to the home can be significant.
 
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Old 11-14-01, 05:00 AM
Larryz
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Vapor barrier

Thanks Twelvepole I think that I will do that in my space, I plan on insulating under floor anyhow, so it can all be done at the same time.

OT, I looked at your website (very nice), what are your thoughts on Pergo or Uniclic flooring? I am about to do a floor for a new dining room that is being put in. Also, if I wanted to find someone to match existing oak cabinets that have, how would I go about doing that? Should I just call some people that do cabinetry?
Thanks, Larry
 
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Old 11-15-01, 01:08 AM
T
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Plastic laminate flooring

If you are in the market for plastic laminate flooring, visit www.azfred.com. Also, at www.ifloor.com you can find additional information as well as info on brands.

Matching existing kitchen cabinets may be a challenge. If you know the name of the manufacturer, it may be possible to locate a dealer which carries your line of cabinets. Cross your fingers that it is not a line that has been dropped. If the cabinets are not going to be on the same wall or in the same run of cabinets, it may not be necessary for an exact match. For instance, if you are going to do an island or wall unit on a separate wall, you can get away without an exact match.

Check the doors and drawers to see if there is any indication of a manufacturer if your cabinets are manufactured cabinets. Usually, a web search will turn up a dealer in your area. You can take a door with you to see if they still manufacture the door style.

Best regards,
 
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Old 11-15-01, 07:44 AM
rbisys
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Gretings,

Depending on what part of the country you live in, installing fiber glass under a wood flooring could lead to problems because of the condensation. The radiant barriers are the only way to insure you will not have problems.

Thank you for considering my opinion.
 
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