Spray foam insulation

[Joe Cowan]

I am starting the process to have my crawlspace batt insulation replaced with spray foam. The first guy I speak to wants to spray the exterior walls down to the dirt and place a vapor barrier on the dirt and not spray in between the joist. That surprised me as I assumed the spray would replace the fiberglass insulation. Anyone with knowledge on the best way to insulation a crawlspace?

[Roy Petersen]

I'm no expert, but spray foam in contact with soil and moisture is a bad idea. Not only will that facilitate it breaking down faster, but there's a decent chance things like ants and termites will find that inviting, since it will hold moisture, typically. I'd say the best course (again, not an expert by any means) is to do the underside of the floor. That would likely have the most direct insulating benefit with less ground contact, reducing related issues.

[Todd Mason-Darnell]

I'm no expert, but spray foam in contact with soil and moisture is a bad idea. Not only will that facilitate it breaking down faster, but there's a decent chance things like ants and termites will find that inviting, since it will hold moisture, typically. I'd say the best course (again, not an expert by any means) is to do the underside of the floor. That would likely have the most direct insulating benefit with less ground contact, reducing related issues.

This can be a concern, but it depends on the type of foam the contractor is using-open or closed cell. Closed cell is impervious to moisture, insects and rodents. I would highly, highly recommend close cell. It will be a bit more expensive, but worth it.

In terms of the OP's original question, it depends. What part of the country are you located in?

If you are in the Northern climates, where there is freezing weather and snow to worry about, you are correct about putting the insulation as close to the conditioned space and allowing a ventilation space between it and the shell of the building.

If you are in the Southern, hot/humid climates, the best build science now says to put the insulation on the outer shell of the build and seal up as much of the ventilation between the shell and the exterior as possible (look up "hot roof).

The benefit I could see of spraying the exterior of your crawl space with closed cell is that it would form a wind and vapor barrier, which would make the batts more effective (assuming your crawl space is not damp.

Could also be that this contractor doesn't the hassle of going into the crawl space.

I would definitely get some more quotes.

[Ed Labadie]

Had my crawlspace foamed years ago. Went from the dirt all the way up, sprayed the rim joist and the floor about 1' in.

The rim joist & floor were important as my house is balloon construction, next to impossible to seal that area with anything but foam.

Ed

[Chris Padilla]

Do some searching of "closed or open cell foam insulation" to see the main differences to help you choose one over the other. Closed cell can be used below grade as it is impervious to water. Open cell cannot be used below grade. Closed is the best choice in most situations but one word of caution if you do your crawl space with closed: if you need access to electrical or plumbing, closed requires tools to chop into as it is really stiff. You can't grab it with your hands and rip out chunks--you can do that with open.

[Greg R Bradley]

Doing the crawlspace that way makes perfect sense. You stop the moisture before it enters the crawlspace. If it is in a cold environment, the next step is insulation below the crawlspace. Leaving the existing fiberglass at the joists is the next step of insulation and allows you to move that around to work on plumbing and electrical. Best way to insulate in hot/humid climate.

Look at it this way: Moisture barrier and first step of insulation where the crawlspace meets the environment. Second step of insulation between the crawlspace and living area. Very much like insulating the attic at the roof and having the attic stay closer to the inside of house.

[Nike Nihiser]

I don't want to get into an argument with anyone but, closed cell foam is not impervious to insects and probably not to rodents either (unless it has an insecticide in it, which is rare as I understand it). Google Joe Lstiburek, probably the foremost authority on insulating, air movement , etc.

[Jim Becker]

It's normal to closed cell spray foam the foundation walls like you describe...it was required by code for our addition in 2008, as a matter of fact. Some folks consider that a replacement for insulating the floor because they feel that insulating the perimeter will negate the need to do the floor. However, my personal feeling is that the perimeter is important...and should be done...but a couple inches of closed cell spray foam will help keep the floor even warmer and also add some structural stiffness benefits that can often be experienced with less squeaking, etc. And yes, there should be a vapor barrier on the soil in the crawl space...it's another code thing and a good practice.

[Greg R Bradley]

I don't want to get into an argument with anyone but, closed cell foam is not impervious to insects and probably not to rodents either (unless it has an insecticide in it, which is rare as I understand it). Google Joe Lstiburek, probably the foremost authority on insulating, air movement , etc.

Yes, Joe's articles collected at Building Science is the main source for info on this subject. He has an article from a few years ago, Info-512 that condenses and simplifies the previous info on crawlspace insulation. The super short version is "consider a crawlspace to be a mini-basement". Here is a picture I saved from that article showing the basic idea:

[roger wiegand]

The current standard in MA for better grade construction is now a closed cell form applied to the exterior of foundations (talking full basements here, not crawl spaces) as both the insulation and water seal. It is coated with some sort of yellow paint after it's applied. I'm told it is a good termite barrier as well. It's going on to a lot of houses, so I hope it works! We have it on our new addition, as well as blue foam on the interior side of the basement walls and 4" of foam under the slab. It's the most comfortable basement I've ever had. We're in the middle of two weeks of near zero or below (F) and staying quite warm and happy.

[Jim Barkelew]

The Building Science info on conditioned crawl spaces is the way to do it. Greg's x-section above is how I did two renovations and it works well. Basically treat it like another room in the house and not have it vented to the outside.