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Crawlspace insulation question

Post in 'DIY and General non-hearth advice' started by OilNoMore, Dec 30, 2008.

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  1. OilNoMore

    OilNoMore Member

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    I need to insulate a small 200 sq/ft crawl space that was built as an addition to the house, which is a full basement. Does anyone have any experience with this? Specifically, I was wondering if using foam insulation would be the way to go here. The joists are 12" apart, not the standard 16", which makes ripping insulation a pain. I don't know what the price is of the spray foam insulation or if it is even something that would be good to use here. Any advice is welcomed.

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  2. coolidge

    coolidge Member

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    As far as i,m concerned the spray foam would be the only way to go. Call a contractor for a quote. I do this for a living, and would think for an r-19 it wouldnt cost you anymore that $600 bucks. Will also keep out the mice and squirells from nesting in any fiberglass. You would want a closed cell foam (2" is a vapor barrier) Hope this helps.
  3. drdoct

    drdoct Feeling the Heat

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    Really $600 for foam? I've got to do my crawlspace and have been dreading it. My dream would be to sprayfoam it to totally seal it, but I always figured the foam guys charged an arm and a leg because the foam kits are very expensive off ebay. I'll have to call someone out.
  4. coolidge

    coolidge Member

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    This would be the ballpark price i would charge in my area. Yours might be different. You will need to contact a contractor( get three quotes and check references). If you are doing a crawlspace dont let anyone talk you into open cell, use closed cell to stop water vapor from entering your house. Also check with local building code officials to see if a thermal or ignition barrier will need to be installed. This will also add to your price.
  5. Highbeam

    Highbeam Minister of Fire

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    I just had my 1300 SF crawlspace insulated to R-19 and the joist spacing was 60 inches, yes 60, so there was some cutting and fitting, strapping etc. They put in faced batts of fiberglass in record time. The batts were either 24" wide. If you cut them in half then you will have your 12" strips and be done with it.

    Fiberglass is really cheap. The labor of laying on your back and putting up batts in pretty unpleasant. The whole job only cost me like 800$. It is very nice to have insulated floors.
  6. hot laupi

    hot laupi New Member

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    I have a similar situation-a three season room attached to my cape style house. The porch floor is not insulated, and have invstigated the best way of getting this done. Before I start sounding like a know it all, I warn you that i am a project manager in a residential architectural firm, and spec'g insulation and climate controls is a big part of my job.

    Spray foam works great, but is very expensive, even as a DIY. Someone posted here that they would charge 600.00 to do it-give me a call, you can come over tomorrow!!! I don't think i could get a wholesale foam kit for less than 600.00. BTW, did you ever try to foam in a wall-much less a crawlspace floor? There is def. some skill/learning curve involved; I would not reccomend attempting this on your own for the first time.

    Look into 2" rigid insulation, with a vapor barrier on one side. Installed on the underside of joists and properly taped at the seams, this will allow the floor cavity to breathe as necessary to prevent mold, & will stop drafts. This method will truly cost a fraction of fthe foam in price, and can truly be done on your own. This will get you about R10 insulation value. Do not worry about getting a R19 rating on the floor, stopping the cold air & drafts from getting into the floor package does most of the work here.

    Obliviously, stay away from batts, & poly vinyl vapor barrier for this application. This will cause mold to grow as the humidity changes. No exceptions.

    Check out the Building Science website for more information on this topic-search for "insulating a crawlspace" and you will find a more in-depth explanation on the above.

    Good luck!
  7. coolidge

    coolidge Member

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    I will agree with you hot laupi, as for the 600.00 charge i suggested was for 200 sqft. You could do this job for probally 200 buck with fiberglass I also agree about what will happen(mold,mice ) with fiberglass. The problem with foam board (i dont meen to offend anyone) is the installer. As for spray foam there is no cutting or taping and it fits every time. 2" inches will do the job, which will give you somewhere between R- 10 to R-14 for a closed cell foam also the 2" will give you a vapor barrier. As you know building science has changed alot over the years and heating and cooling has gone through the roof. There are alot of articles written from Oak Ridge about the use of spray foam and its ability to control costs. Google Mason Knowles, he also has really good articles.
  8. OilNoMore

    OilNoMore Member

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    Thanks for all the great advice. The cost of the spray foam is going to be too much. I spoke with a contractor friend and he said there is not really anyone in our isolated and rural area that does it, which means an hour drive or more from most professional contractors with expertise in this area.

    I think I'm leaning toward the rigid insulation, but I do have a couple of questions. First, should I put a vapor barrier of plastic sheeting down on the ground before doing anything? I've read a few articles that say to do this. Also, is there a specific side of the rigid insulation that I would need to make sure faced toward the house or down toward the ground? If so, which side goes where? How do you recommend installing it? Someone stated that one of the problems with the rigid insulation was the person installing it. I want to do this myself but don't want to waste my money and time doing it incorrectly. I know there are special nails you can use to put it in but that's about the extent of my knowledge of this material.

    Should I also look to insulate the walls of the crawl space? The area in question is a crawl space addition that connect to the full basement foundation of the rest of the house. Currently we have no heat source in our basement, but in the future we likely will install something, be it an old wood stove or other I'm not sure. The basement is partly finished and done by someone who really used their head. The finished area is framed in 24" from the basement walls, so as to allow access all around the finished part and to the pipes, electrical and floor of the first story.
  9. LLigetfa

    LLigetfa Minister of Fire

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    My former home had a crawlspace with dirt floor with poly covering it and draped up the walls. The contractor had stuffed the the 2x6 stud spaces with 3-1/2" fiberglass batt insulation and made it look full so there was a space on the cold side. Moisture came up from the ground under the poly and condensed in the insulation. I had to pull down all the poly, and pull out the insulation and dry it out. I priced out spray foam insulation but it was way too expensive so I bought rigid foam that I cut to fit the stud cavities. I also cut blocks of foam to seal the bottoms and put back the fiberglass after it dried. The foam went on the cold side and the glass on the warm side. That way, the dew point was in the foam so that there would no longer be opportunity for condensation in the glass batts.

    When I put the poly back, I strapped it down with lath to seal it to the foam blocks on the bottom so that ground moisture could not migrate back up into the walls.

    It sounds like the OP wants to insulate the underside of the floor rather than the perimeter. Depending on how deep the foundation is, the crawlspace may need to be kept heated to prevent the frost from getting under it and you may need to insulate only the preimeter.

    Insulating the floor is quite a challenge since the vapour barrier has to be on the warm side of the insulation. It is for that reason that spray foam is the only viable option. In my case, the floor was not insulated. My current home also has a crawlspace that has insulated walls and a concrete floor. It is essentially a basement for midgets and considered conditioned space that I heat. The result is nice warm floors.
  10. LLigetfa

    LLigetfa Minister of Fire

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    Oh, the other thing you have to consider is whether or not the crawlspace is considered conditioned (plenum) space. If it is, most building codes don't allow exposed foam insulation unless it meets certain criteria. Check with the installer.
  11. d.n.f.

    d.n.f. New Member

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    I did a crawlspace on a 1000 sq house. Just bare walls so I glued r10 rigid. The problem was that it got a ton of water down there so I didn't cover with drywall. Sometime got ten inches of water (gravel floor) and you couldn't pump it out as this was the water table. So no drywall and hence against code. Verbotten.

    It did make a huge difference in the warmth of the floor.
  12. coolidge

    coolidge Member

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    The foam board is great stuff ( i like the Atlas board foil faced on both sides)R-7 per inch. Plastic should be place on the dirt before the install ( you wont get as dirty lying on your back) to keep moisture down. As for installing the foam board use the old saying "measure twice cut one" try and get as snug a fit as possible and either use foam cans or caulking to seal the edges. You can use a scrap piece of wood, pound on the face of the wood to drive the foam board in depending on thickness of material. It actually takes quite a beating. Yes you will have to check with your local building codes to see if the fifteen minute ignition barrier is required in your area ( if going with sprayfoam). There is a water based paint that will do this job for you, if you go by the manufactures recommendations. Website for the paint is www.tpr2.com
  13. LLigetfa

    LLigetfa Minister of Fire

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    Spray foam can be very flammable. On pipeline construction they replaced sandbags with spray foam "pillows" to set the pipe on in rocky ground before backfilling with sand. They were welding too close to some of it and it went up in a huge ball of flames in seconds.

    I realize not all spray foam is as flamable, but I'd be worried with rigid foam too. There is a rigid fiberglass sheet made for foundation walls that you can place next to the foam board instead of drywall. You can also blow stucco directly to the foam board with one of those popcorn ceiling applicators.
  14. Jack Straw

    Jack Straw Minister of Fire

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    If the floor is concrete in the crawl space a 4 wheel dolly or a mechanics creeper works nice when working there.
  15. hensonconst1

    hensonconst1 Member

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    Don't forget guys putting a petrolium base insulation against wood causes swetting and will eventually cause rot.
  16. bridgham

    bridgham New Member

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    My situation is similar, but worse... My kitchen was added on to my 1890 house sometime in the 50s I think, maybe earlier. It has a sloped dirt floor crawl space underneath that goes from about 20 inches where it meets up with the basement, to about 4 feet where the access door is.

    Unlike many descriptions here, it has a tumble-stone foundation.

    It also has maze of pipes, drains, vents and wiring for the kitchen, a bathroom, the washing machine, and two radiators. There is a mishmash of fiberglass batting stuck up between the joists, foil facing down I think, and a bunch of uninsulated pipes and some insulated (with asbestos insulation!).

    It's pretty dry in there, gets a little spot of dark earth on the lowest of the 4' side. There is 2 x 3 foot opening into my (not much better off) basement where I have a humidifier running. There are no rotting issues, smells, or rodents, that I am aware of... yet.

    With not much money, am I screwed here or what?

    How can I insulate that tumble-stone? How can I put plastic on the floor with nothing to attach it too? How can I re-insulate that floor through the maze of pipes?

    Aaarrrggg!

    ~eric
  17. oldbrownhat

    oldbrownhat New Member

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    My gf's place in Bellingham WA has a similar situation. It is a 1900 sf rancher built in 1966 with an uninsulated ventilated crawlspace. and plastic vap. barrier on the ground. Heating is by HW baseboard fed from a high-eff. boiler. (I'd really like to put a pellet stove in the unused gas fireplace some day, though.) Unusually, the floor is on 4"x6" beams on posts, rather than the usual joists 16 or 24" o/c. Of course the floors are quite cool and with the recent massive hike in NG prices from Cascade we have decided to insulate the crawlspace for next winter. We haven't yet priced having foam sprayed in but I am guessing about $2-3k. Due to the water supply and waste lines under the floors I suppose this would be the least hassle.

    Would using a reflective radiant barrier (such as Reflectix) be a possible alternative? I have read conflicting opinions on the real-world performance of these products. My main concern would be trapping moisture between the barrier and the underside of the floor, but leaving some openings for ventilation might prevent this (?) I'm also not sure that this alone would provide enough benefit.

    :) Stuart
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