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Old 11-22-2010, 01:11 AM   #1
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insulating a crawl space...need some help


hi,

i live in NH and need to insulate a crawlspace beneath my living room. its only about 3 feet high with a dirt floor.

what do i do for insulation? i need to do the rim joists and the floor. for the rim joists, i was thinking roxul insulation topped with foam board. what about between the floor joists?

thanks,
mike

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Old 11-22-2010, 09:52 AM   #2
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insulating a crawl space...need some help


Search the forum, lots of info on this in previous posts. Here is a link I like:
http://www.buildingscience.com/docum...n-crawlspaces/

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Old 11-22-2010, 10:42 AM   #3
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insulating a crawl space...need some help


i think the best long term would be to do it with spray in foam. its going to be more expensive, but worth it in the long term.
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Old 11-22-2010, 12:45 PM   #4
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insulating a crawl space...need some help


Quote:
Originally Posted by mklang View Post
hi,

i live in NH and need to insulate a crawlspace beneath my living room. its only about 3 feet high with a dirt floor.

what do i do for insulation? i need to do the rim joists and the floor. for the rim joists, i was thinking roxul insulation topped with foam board. what about between the floor joists?

thanks,
mike
Hey Mike,
My name is George and I work for a Chicago area Home Depot. How to insulate your crawl space depends on whether it's ventilated or unventilated. If you have an unventilated crawl space DOE recommends to only insulate your walls rather than ceiling and walls. The reasoning behind it is that if your walls are completely insulated you are saving on the insulation and achieving the same results. When using this method your crawlspace needs to be completely airtight and air barrier maintained, also in addition you need to seal access panel(s) and provide supply outlet for the return air. Further, you need to provide a 6mill vapor diffusion retarder along the dirt floor and extend to about 6” along the wall perimeter.
If you have a ventilated crawl space you need to seal all gaps and opening s (mechanical opening etc. check with local code council on fire rating) between your floor joists, add a fiberglass insulation and a vapor barrier such as Tyvek or 6 mill plastic. In addition you also need to add a vapor barrier along your dirt floor; vapor barrier use depends on home usage and climate so please visit link provided to see what applies to your area. Hope that helps and good luck with your project.
http://www.energysavers.gov/your_hom.../mytopic=11480
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Old 11-22-2010, 05:39 PM   #5
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insulating a crawl space...need some help


Your State is in a high or moderate radon area: http://energy.cr.usgs.gov/radon/rnus.html
Because of this, please check with your local B.D. before closing off your crawl space. If you live near a river, lake or bottom of a steep valley with a high water table, leave it vented to help dry.

If your zip starts with 031 or close, it’s recommended to use R-25 in the floor for a vented crawl. Always install a v.b. plastic over the dirt.

If your B.D. ok’s the conditioned crawl, follow their requirements for the insulation. The DOE’s site shows an option “B” which is not recommended by Building Science as fiberglass batt insulation is air permeable and will not stop any interior moisture from condensing on the concrete wall . Better to use rigid foam board and be air-tight (just like a basement).
The rim would be foam board (air sealed) with Roxul after it.

"
If you have a ventilated crawl space you need to seal all gaps and opening s (mechanical opening etc. check with local code council on fire rating) between your floor joists, add a fiberglass insulation and a vapor barrier such as Tyvek or 6 mill plastic." ----- George, could you please explain where I did the bold?

Gary
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Old 11-22-2010, 06:38 PM   #6
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insulating a crawl space...need some help


I live in the Chicago area and this is what I did in my 48" high crawl space...

1) poured a 4" concrete slab in the crawl space;
2) sealed up the vents and around the sill plate;
3) Glued a furring strip to the top of the concrete walls and nailed unfaced insulation;
4) One of the HVAC ducts runs through there and with the combination of my dehumidifier, it maintains 40% humidity at 60-65 degrees year round.
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Old 11-23-2010, 10:11 AM   #7
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insulating a crawl space...need some help


Good call Gary... my bad peoples , no more free hats from DuPont after this...Tyvek it is s not a vapor barrier.

Gary i was trying to explain that fiberglass batt insulation doesn't work if exposed to the wind so in some instances needs to be covered with an air barrier such as Tyvek or vapor barrier such as 6 mill visqueen whatever his local B.D calls for.
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Old 11-23-2010, 02:02 PM   #8
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"Gary i was trying to explain that fiberglass batt insulation doesn't work if exposed to the wind so in some instances needs to be covered with an air barrier such as Tyvek or vapor barrier such as 6 mill visqueen whatever his local B.D calls for." ----- I could not understand why you used them side by side without explaining the house wrap would go on the crawl side and the v.b. would go on the heated (room) side. B.D would not call for a house wrap down there in any case. It's easy to say the wrong thing and easy to type the wrong thought, been there, done that.

Howard, sounds like you did a lot of work and you are almost there. Unfaced fiberglass batt insulation is very air permeable (furnace filters made of it) and may cause problems with moisture:
“Crawlspace walls should be insulated with non-water sensitive insulation that prevents interior air from contacting cold basement surfaces—the concrete structural elements and the rim joist framing. Allowing interior air (that is usually full of moisture, especially in the humid summer months) to touch cold surfaces will cause condensation and wetting, rather than the desired drying. The structural elements of below grade walls are cold (concrete is in direct contact with the ground)—especially when insulated on the interior. Of particular concern are rim joist areas—which are cold not only during the summer but also during the winter. This is why it is important that interior insulation assemblies be constructed as airtight as possible.” Bolds are mine, from: http://www.buildingscience.com/docum...d%20in%20walls

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Old 11-23-2010, 02:46 PM   #9
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insulating a crawl space...need some help


Gary thank you for the knowledge.
I'm trying to understand something ....and there is something new to learn every day.
First let's say if you have a vapor barrier along the dirt floor that is extending on to the walls for about 6".
Second you have an unf. fiberglass over the wall coming down and overlapping the extended vapor barrier.
And finally additional vapor barrier over the fiberglass from the sill plate coming down to the dirt floor.

Wouldn’t that be air tight and vapor tight?
Thoughts?
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Old 11-23-2010, 07:56 PM   #10
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A good read, and fig.9: http://www.buildingscience.com/docum...ts?full_view=1

Gary
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Old 11-29-2010, 07:19 PM   #11
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insulating a crawl space...need some help


probably a stupid question, but how do i know if my crawlspace is vented or unvented? the crawlspace, and room over it, was built in 1959 and is not anything fancy. i don't think the person who built it even thought about making it "vented" or "unvented" by design. it is concrete block with a dirt floor. there are no window or other exhaust ports of any kind. the only opening is the access panel in the basement. i'm assuming it is unvented?

like Gary said, i'm concerned about radon and don't want to force it up into my living room. i'm thinking i'd like to properly vent it to push the radon out and install the insulation per recommendations for a vented space.

thoughts? thanks!
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Old 11-29-2010, 07:20 PM   #12
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insulating a crawl space...need some help


probably a stupid question, but how do i know if my crawlspace is vented or unvented? the crawlspace, and room over it, was built in 1959 and is not anything fancy. i don't think the person who built it even thought about making it "vented" or "unvented" by design. it is concrete block with a dirt floor. there are no window or other exhaust ports of any kind. the only opening is the access panel in the basement. i'm assuming it is unvented?

like Gary said, i'm concerned about radon and don't want to force it up into my living room. i'm thinking i'd like to properly vent it to push the radon out and install the insulation per recommendations for a vented space.

i'd like to go spray foam but its not in the budget and will be doing the work myself. thoughts? thanks!
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Old 11-29-2010, 08:24 PM   #13
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insulating a crawl space...need some help


sorry, i'm kind of talking to myself out loud here.

i've done some more reading and, assuming that i have an unvented crawlspace, i'm thinking of leaving it unvented because adding vents seems silly. i could then insulate the walls and rim joists rather than the floor. i figure i can do this first and then take an air radon sample and see if i need a radon mitigation system.

again, this is assuming i have an unvented space...which i'm hoping someone can confirm...
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Old 02-07-2011, 12:02 PM   #14
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insulating a crawl space...need some help


Q - "how do i know if my crawlspace is vented or unvented? the crawlspace, and room over it, was built in 1959 and is not anything fancy. i don't think the person who built it even thought about making it "vented" or "unvented" by design."
A - Crawl space vents are usually window like openings to the outside, sometimes with some sort of grate to keep wildlife out.Vents are usually required by building code in many , specially in areas where radon is a concern. They've been required since the 50's when crawl space type foundations became a popular alternative to basements.
However, back when most of these codes where written, we did not understand building science as we do now. Today we know that crawl space vents are a bad idea, no matter where you live.

The best way to treat a crawl space is to have it encapsulated: which means, unvented, completely isolated from the outside with a sturdy vapor barrier, air sealed and then conditioned.

However, please keep in mind that, even if your crawl space doesn't have any visible vents, it doesn't mean it is free from trouble because it is not yet air sealed or conditioned. Moisture from the ground and from the outside will still get into the crawl space, and depending on what kind of insulation you use, you might be setting yourself up for mold and structural decay in the future.

Please consider for a number of reasons:

- It will control moisture and will cut energy losses through the crawl space. You might not need insulation after all.
- Because it seals the crawl space from the outside it serves as a passive radon barrier as well. If further mitigation is necessary, professional grade can be fitted to work with a radon mitigation system.
-

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Last edited by Gary in WA; 02-07-2011 at 02:04 PM. Reason: Ad link in post body
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