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Crawlspace - options for insulating/vapor barrier-ing?

Crawlspace - options for insulating/vapor barrier-ing?

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  #1  
Old 12-06-14, 04:18 PM
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Crawlspace - options for insulating/vapor barrier-ing?

Wondering if we should do anything to insulate our crawlspace in some way.

Its a cement floor, unconditioned, with a few very small windows (that open) to the outside. The "ceiling" of the crawlspace has the pink batt insulation, but the people before us installed it upside down/reverse.

Would it be worthwhile to i) spray foam insulate the walls of the crawlspace, ii) spray foam insulate the "ceiling" of the crawlspace, iii) just have the pink batt insulation installed correctly, iv) put a vapor barrier on the floor, v) a combination of any of these, and/or vi) something I'm not thinking of. If I can only do one or two, what is most cost effective?

Thanks for any advice.
 
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  #2  
Old 12-07-14, 04:27 AM
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There are two schools of thought regarding this. One totally encapsulate the crawlspace, including the windows and condition the air. The other allow for proper air flow across the crawlspace using foundation vents. Your pink insulation should have the kraft facing up toward the living space. Spray foam will be horribly expensive, but viable. Vapor barrier overlapped and taped on the floor definitely.

In our area (Deep South) we ventilate our crawl spaces and insulate/vapor barrier properly. In other parts of the country that won't work, and encapsulation is the best alternative. It is more than putting up foam boards on the walls, though. Hang in there as our guys will check in slowly and offer differing opinions. Sadly, you will have to choose. Good luck with the project.
 
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Old 12-07-14, 08:42 AM
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Thanks for the info.

If we do decide to encapsulate, is that something that a weekend warrior DIYer can do? (As in, I can replace a sink and faucet, but to install a whole house fan I had a much, much better DIYer help me; if that gives you an idea of my level of [non]expertise.) Or would a professional be needed?

If we do encapsulate, would I need to put an A/C vent (and possibly a heating loop?) down there to actually condition it? Or does "conditioned" just mean that its not exposed to unconditioned elements?

For the vapor barrier - its incredibly dirty down there from the previous owners. Can the vapor barrier be put over the dirty cement floor, or would I need to clean it all first? Its a crawl-on-hands-and-knees crawlspace (although not a squirm-on-your-stomach crawlspace). Basically, not a fun place to spend a lot of time in.

We currently have two dehumidifiers down there that run throughout late spring to early fall (and drain to the sump pump) - if we encapsulate, could we get rid of those?

Last question (for now!) - you said encapsulating with spray foam is horribly expensive. Any (very) rough estimates on what I could expect from a professional for doing one wall, 100' long and about 3.5' tall? (From that, I can extrapolate and figure out what it might cost me, at least ballpark figure.)

Thanks yet again.
 
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Old 12-07-14, 09:05 AM
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I much prefer to encapsulate, of course I'm north of you so venting is not an option. But once encapsulated the floors will stay a bit warmer along with any pipes or appliances.

Since you are running 2 dehumidifiers I would assume a plastic vapor barrier on the floor would be a plus, but you will not want any water issues. Do you get water at various times of the year?

Sheets of foam or spray on should be covered with a fire barrier. One way to eliminate the extra step and expense is to use an approved foil faced insulation panel, like Dow Thermax. But check with local code enforcement as some will accept the standard foil faced board from the box stores. I believe Thermax has a bit heavier foil covering. But just taping the seams and edges completes the job.

As a rough estimate for spray foam I use $1 per board foot, one sq ft one inch thick. But companies will probably charge more for small jobs in tight places.

I'll add a related link for some reading.
Photo #5 would be nice .
BSI-009: New Light In Crawlspaces — Building Science Information

BSD-103: Understanding Basements — Building Science Information

Bud
 
  #5  
Old 12-07-14, 10:55 AM
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We don't currently have water issues, and I've never seen water down there (other than after a huge thunderstorm for a few hours).

We've been here about 3.5 years, and the inspector when we purchased said there was a water line in the crawlspace. Of course, the people before us had their gutters drain right next to the foundation, didn't have a decent sump pump and never had dehumidifiers. So, we extended the gutters to about 2-3 feet away from the house, put in a good sump pump and added dehumidifiers. No water issues.

Would I still need the dehumidifers with a vapor barrier? It costs about $125/month to run the 2 (using a Kill-A-Watt EZ detector, anyway).

Is it a waste of time to just do a vapor barrier on the ground and not do anything to the walls? I'm just looking for the most bang for my buck, and it sounds like a vapor barrier is relatively cheap and that doing the walls is much more expensive.

Last question (for now!): do I need to clean the crawlspace floors before putting down the vapor barrier?

Last last question: which vapor barrier (thickness, brand, anything, etc.) do you suggest?

Thanks again.
 
  #6  
Old 12-07-14, 12:54 PM
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IMO, definitely clean up that space before adding a plastic cover over the floor. Any walking on top of the plastic with stuff under it will ultimately poke holes in it and waste your efforts. As for thickness, you can use inexpensive box store black plastic on up to a 20 mil product specifically designed for that job. Given the limited height I doubt the kids will be playing down there so 6 mil would be the minimum I would recommend.

Insulating the walls is actually not bad, it is air sealing and detailing the rim joist that takes time. I like a layer of rigid cut and foamed in place for the rim, but check with local codes as termite inspections in some areas require access. Caulk or can foam to air seal and then cut and fit Roxul will do a good job.

As a side note, 60% of the air you breathe in your home comes from that crawlspace so it greatly improves air quality to clean it up and seal it.

As for eliminating the dehumidifiers my guess would a complete job would accomplish that and more. I would expect improved comfort, air quality, and lower energy costs.

Bud
 
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Old 01-03-15, 08:09 PM
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Oopey, just curious where you are in NJ? I live in NJ also(Mt Holly) and have ideas for my crawlspace/basement. I've been working on it for a few weeks now sealing my rim joists. Maybe we could compare notes.
 
  #8  
Old 01-04-15, 02:37 AM
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chan's 'zactly right about the 2 schools - seems every few years, thinking changes from conditioned crawl space w/NO vents to vented then back again actually both make sense but you need to be code compliant @ the time the work's done,,, i like power'd foundation vents concrolled by humidistat

6mil plastic's a waste - it degrades over time + you'll eventually poke holes in it,,, better you should buy 19mm pond liner,,, its tough, cheap, & avail @ apron/vest stores

unless there's leaking wtr, 1 decent dehumidifier should be able to handle the load,,, we bought a 70pint on ebay - iirc, $ 225incl frt - fridigaire or something like that

when we had a bsmt wtrproofing co in nj, that's how we handled this work - from allamuchy no less
 
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