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insulating crawl space

Post in 'DIY and General non-hearth advice' started by chrisasst, Jan 23, 2013.

  1. chrisasst

    chrisasst Minister of Fire

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    So my floors are freezing. I can feel the cold air come up through them. Under them is the crawl space. What can I do. When I saw crawl space, I am literally talking about a space a little kid would have trouble crawling around in. I have tried to seal up the outer perimeter. But obviously I need to do something more with that also.
    I am pointing a IR thermometer at my floor right now and it is 38 degrees...
    what can I do? I know carpet would help a little but..

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  2. Highbeam

    Highbeam Minister of Fire

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    You have a couple of options.

    One is to insulate the perimeter walls that hold up your house and then close off all the crawlspace vents. The crawl becomes a warm space and your floors won't be so cold. You need a dry crawl for this so no water issues. Your plumbing will also be in the warm crawlspace which is good.

    The other option which is much more common is to leave the vents but insulate the floor from below. This is what I had done a few years ago and the floors were immediately warmer. I think they used R18 faced FB batts. Hire this job out. It is terrible work crawling around on your back pushing thick batts up against the bottom of the floor.

    Current codes require this floor insulation so the pros know how to do it. They are not afraid of slithering around on their bellies to install the FG.
  3. yooperdave

    yooperdave Minister of Fire

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    Another good application for spray foam...the rigid type, not the retro foam that can be added to walls
    Shane N likes this.
  4. chrisasst

    chrisasst Minister of Fire

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    This is one thing I thought about, but don't know where to start. Does Lowes rent / have this type of machine to do this or is this a leave it to the pros kind of thing?

    And there are, at the moment, no plumbing down there in this crawl space..
  5. yooperdave

    yooperdave Minister of Fire

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    Chrisasst--I would think that someone rents the equipment and materials. I occasionally see them on craigslist around here.
    After too many years of crawling around in crawl spaces, I would definetly hire it out. If it is a 'tight" space like you mentioned, be sure to inspect the job before you pay full. That way, any missed or weak spots could be dealt with.
  6. Highbeam

    Highbeam Minister of Fire

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    Foam application is almost exclusively done by professionals. It is extremely expensive.
    Shane N and ScotO like this.
  7. ScotO

    ScotO Guest

    HB is right. Not to mention it gets pretty warm when doing it. My cousin just had his new house done with spray foam, and man that was unreal. The guy doing it looked like the Michelin man every half hour or so, he had to remove the Tyvek suit and resuit up several times......messy isn't the word for it...
  8. seige101

    seige101 Minister of Fire

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    Definitely look into having a contractor do it. It is probably only a few dollars more than buying the material your self and you don't have to deal with the pain in the ass suck job that it is. Bonus points if your state or local utility company has a program similar to mass save, where they will pick up most of the tab. Something to look into.
  9. semipro

    semipro Minister of Fire

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    Given current pricing and availability, IMO there are only two ways to install foam that make sense:
    - Hire a contractor to spray foam
    - Install board foam products in between the floor joists (eps, xps, polyiso) yourself or have a contractor do that. These are sealed in place with spray foam from a can.

    Fiberglass batts are rarely installed properly under floors. To work well there must be no air gap between batt and floor. You'd need to add an infiltration barrier like Tyvek also to prevent air flow though the batts and into your house.
  10. serveprotect

    serveprotect New Member

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    I am in the exact same situation. Remodeling an old summer kitchen and turning it into a living space. It is not my forever home and ripping up the floor would be a major undertaking. Since i have to build up the floors 2 inches to level with shims i plan on spraying between them with spray foam i have left over from the walls. I did the walls myself with spray foam. The kit came in a propane tank setup and took me about 30 min to do a 300 sf room. Imo it was a very easy diy project. I will add it was more expensive than traditional insulation but sealed up an old room very well. Also, make sure you have the room atleast 70 degrees to make the foam work properly. Do you guys think my plan will work? Figure it cant hurt.
  11. Highbeam

    Highbeam Minister of Fire

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    The pros that did mine used faced batts held up tightly to the subfloor with lots and lots of that nylon string. Seems pretty hard to screw up.
  12. semipro

    semipro Minister of Fire

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    Many will install batts under floors by stapling the facing to the joists.
    This almost always results in an air gap between floor and batt.
  13. Highbeam

    Highbeam Minister of Fire

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    My floors were uninsulated when I moved in. House was built in 1963. The Floors are 1.5" thick T&G decking perpendicular to beams at 5' spacing. So they had to use strings to hold the batts up. Above the decking is tar paper, and then in the kitchen 5/8" plywood and then linoleum. The biggest difference after the insulation was that when you stood in one place on the linoleum it would heat up the floor and then you could find your hot footprints if you stepped away for a second. Before the insulation is was like walking on cold concrete all the time.
  14. daveswoodhauler

    daveswoodhauler Minister of Fire

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  15. chrisasst

    chrisasst Minister of Fire

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  16. begreen

    begreen Mooderator Staff Member

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    We had an estimate for a pro to come and insulate underneath our floors. Same problem, toward the perimeter on a couple sides only a child would fit. I once almost got stuck in there. Guy came by, gave us an estimate that we approved. A week later the crew showed up. The got in the crawl space and about 5 minutes came out, packing their gear. Both said they couldn't and wouldn't do the job.

    That was 2005. Looking back, they were right and even it they could, by now half the insulation would have been rodent nesting. Our "foundation" walls on one side were just stem walls and the south side just rest on a large rough doug fir 8x8. In 2006 we bit the bullet and put in a proper foundation by raising the house 6ft and setting it back down on a new 3ft higher foundation. Now we have a bullet proof easy to work in crawlspace that my son and I insulated. Temp hardly varies down there. This isn't the only option. If your foundation is sound and good and the footings deep enough, you may be able to dig out those low areas instead.
  17. Highbeam

    Highbeam Minister of Fire

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    BG, didn't you do the "warm crawlspace" method where you insulate the stemwalls, bare floor, only a VB over the dirt, and no ventilation?
  18. begreen

    begreen Mooderator Staff Member

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    Correct. We totally tossed out the old plan once the house was raised and on a solid foundation. It's interior insulated with a vapor barrier over the dirt. The space is ventilated in the summer, but not in the winter. All the ductwork, hot water heater and hot water pipes are insulated in the crawl space. It stays a pretty constant 60-63F all winter long with no supplemental heat.
  19. semipro

    semipro Minister of Fire

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    Why is summer ventilation needed?
  20. begreen

    begreen Mooderator Staff Member

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    Prolly not necessary, but it's easy to do. I tried going a year with it closed and find it smells a little musty after a while. Also, my "vents" are nice big 18" square holes with galvanized screen on them. This is where the large I beams went through to support the house when it was airborne. When they are open it lets in daylight like a window which is nice.
  21. Cross Cut Saw

    Cross Cut Saw Feeling the Heat

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    I insulated two crawl spaces under my home, one was an addition that was built in 2010 so the boards were nicely spaced 18" on center (I think) and 96" long. It was very easy and I was able to get insulation bats that exact size and put them in held up by rods.

    The other space was a project from hell. It was a very tight fit for me (6' 240lbs.) but I slithered around on my back and stomach for a day doing it. It was an old carriage house that had been attached to the back of our house by the previous owners and used primarily as a 3 season space. The floor appears to be framed by a drunken sailor, from 16" on center in some parts to 24" on center in others. So to use those same bats I had to turn the bat sideways and cut each and every piece so that I could cram it into the space. I can't remember how many pieces it took but it was the worst experience of any DIY project I've ever done...
  22. Trilifter7

    Trilifter7 Feeling the Heat

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    Has anyone ever heard of using the foam sheets to insulate the floors? I am considering putting them against the bottom of the floor joists and taping the seems to give an insulated air lock between the floor and the bottom of the joists. Not sure if this would actually work but seems like an easy way to do it.
  23. semipro

    semipro Minister of Fire

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    I think this would be okay. It would be much better if the space between the joists were filled with insulation. Alternatively, you could install foam board between the joists and against the floor, sealing it in place with canned spray foam. Additional insulation could then be added with a housewrap installed along the bottom of the joists to stop air infiltration.
  24. Trilifter7

    Trilifter7 Feeling the Heat

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    Thanks for the info. I'm def going to look into it more.
  25. woodgeek

    woodgeek Minister of Fire

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    I'm late to the party, but I want to say that if your floors are 38°, that is not an insulation issue so much as an airsealing issue. You crawl is cold due to stack effect hoovering outside air into your crawl, either through a vent you missed, around the rim joists, sill plates etc. Rather than insulating the floor, I think you would get better ROI spray foaming the rims and closing the vents, and then insulating the perimeter (if needed).

    You could also get a warmer floor by airsealing the top of the house. Air comes in has to go out somewhere. You feel where it comes in and blame that, but seal where the air is going out, and your floor will get warmer.

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