Crawl Space Insulation

Blog entry by Huckleberry posted 04-17-2008 03:45 AM 8856 reads 0 times favorited 9 comments Add to Favorites Watch

I was taking a building codes class a year ago or so and we got on the subject of crawl space insulation. According to the building codes in my neck of the woods they require insulation between non-conditioned air and living spaces. So as I was going to do this in my older house one person told me not to do that. He had said that with a crawlspace that has a moisture issue that it could lead to rotting of my floors. Has anyone else heard this or is this just some bull?

-- I honestly think it is better to be a failure at something you love than to be a success at something you hate.

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5 posts in 5349 days

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9 comments so far

View boboswin's profile


14 posts in 5351 days

posted 04-17-2008 01:08 PM

As I understand it moisture come sup from the ground and you would have to completely seal the joists before applying the insulation. You could look into getting a spray foam insulator in to seal the joists permanently.They can be in, on and out in about two hours.
The insulation factor is huge and the price is competitive if you subtract prep labour costs.


-- I'm still learning

View Dan Lyke's profile

Dan Lyke

331 posts in 5351 days

posted 04-17-2008 04:04 PM

We’ve been looking at putting insulation between our crawl space and our floor, and I’m having trouble finding a technology that I like. The concerns are:

  • Fiberglass seems to be a haven for rodents.
  • Anything else seems to be impermeable to water, creating a vapor barrier.

Normally a vapor barrier isn’t a bad thing, you put it on the inside of your insulation, but in this case I’m afraid that any condensation is going to pool on it and cause real problems. And, during the rainy season out here in California, that crawl space gets really wet.

I’m in a completely different climate than you, but I’m really interested in the solution.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/

View boboswin's profile


14 posts in 5351 days

posted 04-17-2008 07:57 PM

Now you drop the other shoe! <vbg>
Why do you folks build crawl spaces with the kind of weather you have to deal with?

I’m stumped, never had the situation present before.
Sorry I couldn’t help.


-- I'm still learning

View Brian H's profile

Brian H

9 posts in 5351 days

posted 04-17-2008 08:37 PM

Is the crawl space vented? If it can get air, being damp isn’t as much an issue. If it’s not vented and damp, then you are going to have some major issues down the road. (Been there already on my place)

-- Brian

View Huckleberry's profile


5 posts in 5349 days

posted 04-18-2008 03:58 AM

Yes the crawl is vented, but not to my liking. There are only two vents on the same side of the house. Bad news, foundation is poured so adding any more will be a tough job.

-- I honestly think it is better to be a failure at something you love than to be a success at something you hate.

View boboswin's profile


14 posts in 5351 days

posted 04-18-2008 02:14 PM

They cut concrete up here with a high pressure water gun.
You might want to check that out in you area. ( it’s about a 15 minute job for what you need)

It you are on a tight budget (who isn’t) try renting a hammer drill like a Hilti for instance.
That about an hour job but not too difficult.


-- I'm still learning

View Dadoo's profile


30 posts in 5351 days

posted 04-19-2008 01:11 PM

My house is required to have at least R-25 insulation in the floor over the crawl space. I’m going to install a radiant floor heating system this summer, then insulate, then staple a vapor barrier (Tyvek house wrap) over the whole thing.

Something else you might consider (and it works) is to place the vapor barrier (usually plastic sheeting) directly on the ground. You also have to ventilate the crawlspace as a natural air exchange will help keep it dry. Simple registers in the walls will allow this and still keep rodents out.

-- Dadoo!

View Joey's profile


82 posts in 5349 days

posted 04-19-2008 05:27 PM

This is tough issue, me personally living in a house for five years that didn’t have a insulated crawl space, there are more things to consider than just heat and cold penetration. there is also the issue of mold and mildew that can grow on even the most well vented crawlspace. I was reading in fine homebuilding and they recommended that you insulated the crawlspace and seal the whole area with a vapor barrier. if you go to there web site you can try their free 14 day subscription and do some research.

We had to move out that house because of the mold. here is what I wish I would of done, but it wasn’t my house and the landlord wouldn’t pay for the improvements even when I offered to do the work for free.

1st, I would of dug a french drain,
2nd, put the gutter back on the house (yes he removed them said he didn’t like them really they fell down)
3rd, put a sump pump well and a sump in the crawl space, gravel, and VB on the ground and up the side walls of the crawl space,
4th, 1 1/2 foam board on the side walls,
5th, R25 insulation in the floor joist,
6th, Tyvex stapled to the bottom of the joist,
7th, insulated all the heating ducts
Now that is what I would of done based on my experiences and this house. now yours might be different but not to have no insulation in your crawl space is not in my opinion a wise choice. I hope this helps in some way

-- Joey ~~ Sabina, Ohio http://sleepydogwoodworking.wordpress.com/

View CyFree's profile


10 posts in 5270 days

posted 06-23-2008 05:42 PM

There are several independent studies on crawl space moisture control that all reached the same conclusion: encapsulating (installing a vapor barrier) a crawlspace is a good idea. Venting it, with or without the vapor barrier is a very bad idea. Turns out the same vent that lets moisture out, will eventually let it in in humid days and water will condensate all over the liner.

But you don’t need to take my word for it. :)
Some of these studies, are found here:


In other words, if you want to keep your insulation and floor joists safe you want to keep the water out.

According to these studies, the ideal scenario would be a system including a thick (20mil) crawl space encapsulation liner (some contractors use 6mil, but these are know to rip quite easily, specially if you have water heater and other utilities in the crawlspace and people crawling in ion a regular basis for maintenance), completely sealed. A drainage system with a sump pump to eliminate eventual moisture buildup. You can then use either a good dehumidifier, or a lower cost crawl space conditione blowing air from upstairs down into your crawlspace.

Depending on the size of your crawlspace, one of these might just be able to do the job.
To be certain, get a crawl space encapsulation contractor to take a look and make some suggestions. Some offer free consultation, so it will cost you nothing to find out what needs to be done in your case.

Moisture in a crawl space is hazardous in so many ways, from allowing your floor joists to rot and harboring moisture loving pests, to ruining your indoor air quality, because you and your family will be breathing the spores of the mold that will eventually be breeding underneath, feeding on any kind of organic matter available.
The good news is: if you encapsulate and properly condition your crawlspace, it will pay for itself just with energy savings for cooling and heating your home. Not to mention the cost of replacing rotten floors and moldy insulation.

-- "All truth goes through 3 stages: First it is ridiculed. Then it is violently opposed. Then it is accepeted as self evident." - Schoppenhauer

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