Anybody have experience with encapsulated crawlspaces?

[stm317]

Rather than encapsulate and condition the crawl space, I'm thinking about 2" of closed cell foam on the underside of the floor including the joist. That should insulate the house from the crawl space for temperature and moisture. We don't curently have moisture problems down there (20 year old house) and will continue to ventilate. Just looking to tighten it up and cut hearing cost, make it more uniform on temp in the winter. Anybody see something I'm misding?

I think you'd still have wasteful duct leakage into the uninsulated crawl, and you'd need to make sure that any structural wood was completely sealed off with the foam or you'd still have high moisture content in the wood which promotes mold and can lead to warping or decay. You'd also still have effects of moisture/condensation and possibly freeze/thaw cycles on HVAC, plumbing and electrical components which can shorten their useful lives.

It may also cost more. You'd have to do the math for your situation, but insulation tends to cost quite a bit more than vapor barrier materials. And in an encapsulated crawl, you're only insulating the walls which should be less sqft than the floor. The vapor barrier covers most of the sqft of the space, and the super thick, fancy ones cost about $0.35/sqft. Closed cell foam costs $1 or more per board foot, and you'd be doing a couple of board feet per sqft to achieve the thickness you want. You'd have to cover the underside of the floor boards (total sqft of the crawl) plus the cost of the two vertical faces of each joist and the sill plates.

This article is pretty informative: http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

The part that applies most to your question is probably: "According to researchers who conducted a careful study of vented and unvented crawl spaces in North Carolina, homes with sealed crawl spaces with insulated foundation walls use 18% less energy for heating and cooling than identical homes with vented crawl spaces with insulation between the floor joists."

Unfortunately, the link to that specific study is broken, but it's a good read on the subject from a good source.

 

[stm317]

Ummm. I had alot of prep to do like flattening out the dirt and cleaning out old debris. As far as doing the vapor barrier. Id say in the 20-40 hour range working by myself. I had alot of supports i had to go around which takes a long time. If it had been like my current house. With only 5 supports to go around i honestly could get it done in under 20 hours. Also. Ill admit when i work by myself im not super fast. A helper keeps me motivated.

I'd have similar prep work to do. I haven't measured my crawl, but the county says it's just over 1900sqft. I'd probably have more $ in the vapor barrier than you did in your whole project. This being my first time, and the fact that I'm a little bit of a perfectionist, it sounds like I'd need to block out quite a few days if I were to DIY. I guess I won't know if it will be worth trying to DIY until I get some quotes back.

 

[8mpg]

Rather than encapsulate and condition the crawl space, I'm thinking about 2" of closed cell foam on the underside of the floor including the joist. That should insulate the house from the crawl space for temperature and moisture. We don't curently have moisture problems down there (20 year old house) and will continue to ventilate. Just looking to tighten it up and cut hearing cost, make it more uniform on temp in the winter. Anybody see something I'm misding?

This is what I went with just a couple months ago. It wasnt cheap. I paid about $4k to do it but I also had they spray 2" on all the floor joists. It took them 10 hours under the house to do it (24" crawl space). I wasnt about to spend 20-30 hours under my short crawl space myself.

It was amazing how much I could smell the foam while spraying. I read online that 40% of your house air can come from the crawl space. I didnt believe it until they sprayed. My house's musty smell is gone, the floors are a lot more solid. Im very happy I went this way vs a crawl space encapsulation (which probably would have cost at least the same amount if not more).

Check out the article I link just below. I did figure 4 in the drawings.

From my research its a bad idea. The wood needs to breath from what ive heard.

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You are incorrect. The problem is the moisture content of the wood goes up with the humidity of the air. Spray foaming the wood will allow the wood to lose it's moisture content by drying up into the house and over time it will not soak up water. The moisture content in wood from humidity is what causes mold. You want the wood to be dry. Here is an article from Joe Lstiburek from BuildingScience Corp. Hes the godfather of building science:
https://buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces

I think you'd still have wasteful duct leakage into the uninsulated crawl, and you'd need to make sure that any structural wood was completely sealed off with the foam or you'd still have high moisture content in the wood which promotes mold and can lead to warping or decay. You'd also still have effects of moisture/condensation and possibly freeze/thaw cycles on HVAC, plumbing and electrical components which can shorten their useful lives.

It may also cost more. You'd have to do the math for your situation, but insulation tends to cost quite a bit more than vapor barrier materials. And in an encapsulated crawl, you're only insulating the walls which should be less sqft than the floor. The vapor barrier covers most of the sqft of the space, and the super thick, fancy ones cost about $0.35/sqft. Closed cell foam costs $1 or more per board foot, and you'd be doing a couple of board feet per sqft to achieve the thickness you want. You'd have to cover the underside of the floor boards (total sqft of the crawl) plus the cost of the two vertical faces of each joist and the sill plates.

This article is pretty informative: http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

The part that applies most to your question is probably: "According to researchers who conducted a careful study of vented and unvented crawl spaces in North Carolina, homes with sealed crawl spaces with insulated foundation walls use 18% less energy for heating and cooling than identical homes with vented crawl spaces with insulation between the floor joists."

Unfortunately, the link to that specific study is broken, but it's a good read on the subject from a good source.

While I didnt get official costs, I got a ballpark from a company locally in Texas and their cost was going to be quite a bit more. I estimated my costs for 1500sqft of crawl space for materials only and me doing the labor and I was at $1200 or so. The local company gave me an estimate of $4-5/sqft of crawl space due to the 24" height. I may have done my own if I had a much higher crawl space. Literally crawling on your belly for half a week on your days off was not going to happen. I was going to pay a company regardless. Spray foam was the better choice for me (I do not have a/c ducting in my crawl space. It was relocated to the attic (spray foamed as well))

 

[My Old Tools]

From my research its a bad idea. The wood needs to breath from what ive heard.

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Trust me, wood is dead. It doesn't breath. That's why we use finishes.

 

[My Old Tools]

We have no duct work under there. We do have electrical and plumbing penetrations that this would completely seal. As I said, no current moisture problems which is why I shy away from going encapsulated. Once you stop ventilating, the rest of your system better be perfect. Oh, and most of the crawl space is head high, so somewhat easier install. No, I haven't priced it yet. Currently have fiberglass bats with netting. It's getting a bit ragged after the remodel work and just didn't seem to do much this winter.

 

[stm317]

8MPG and My Old Tools, it looks like you are both in TX. Just like our garages, I'm willing to accept that what works well in one part of the country may not work as well in other places.I'm not sure if it's just me, but it seems like crawlspace encapsulation is more common in the Midwest and Mid-Atlantic areas than places that get hotter or are very dry.

If you don't have any HVAC in your crawl, and you don't mind working in the crawl as it is, then maybe encapsulation isn't beneficial for you. For me, it has strong appeal, but I live in a much different environment than you guys.

 

[8mpg]

8MPG and My Old Tools, it looks like you are both in TX. Just like our garages, I'm willing to accept that what works well in one part of the country may not work as well in other places.I'm not sure if it's just me, but it seems like crawlspace encapsulation is more common in the Midwest and Mid-Atlantic areas than places that get hotter or are very dry.

If you don't have any HVAC in your crawl, and you don't mind working in the crawl as it is, then maybe encapsulation isn't beneficial for you. For me, it has strong appeal, but I live in a much different environment than you guys.

To me it was all about the money. My single ballpark was just too much money due to the amount of man hours required to be under the house to do the job properly. Spray foam was cheaper vs professionally installed crawlspace encapsulation ($6k-$7,500 vs $4k spary foam). To do it myself would have been much cheaper. The encapsulation company estimated 2 guys 3 days. Thats 48 hours of labor by professionals under the house. I thought it was overkill but I figured Im better off working overtime at work. Good luck with the quote. I kept reading $10k+ online quotes

 

[stm317]

To me it was all about the money. My single ballpark was just too much money due to the amount of man hours required to be under the house to do the job properly. Spray foam was cheaper vs professionally installed crawlspace encapsulation ($6k-$7,500 vs $4k spary foam). To do it myself would have been much cheaper. The encapsulation company estimated 2 guys 3 days. Thats 48 hours of labor by professionals under the house. I thought it was overkill but I figured Im better off working overtime at work. Good luck with the quote. I kept reading $10k+ online quotes

Seems like the "national average" is around $5k, which is a ballpark I can probably be ok with. If estimates come back in the $10k range I'd definitely do it myself.
Rough estimates for DIY materials would be:
$1000 for 20mil vapor barrier
$100 for tapes
$500 for Foam board insulation (SWAG)
$750ish for dehumidifier
$100 spray foam
$50 misc
--------------
$2500 materials with a decent amount of cushion built in

 

[stm317]

Took awhile to get settled in with the newest family member, but I got the first quote for crawlspace encapsulation yesterday and thought I'd update this for anybody following.

First quote was through a well regarded, larger company with multiple locations in multiple states.
R11 rigid insulation in the walls, Sealing the vents, 20mil vapor barrier, and a dehumidifier- $10,600

I'll be getting additional quotes, but that quote makes my $2500 DIY estimate look pretty appealing. They also had something like a 3-4 month lead time which is a joke.

 

[My Old Tools]

I think you'd still have wasteful duct leakage into the uninsulated crawl, and you'd need to make sure that any structural wood was completely sealed off with the foam or you'd still have high moisture content in the wood which promotes mold and can lead to warping or decay. You'd also still have effects of moisture/condensation and possibly freeze/thaw cycles on HVAC, plumbing and electrical components which can shorten their useful lives.

It may also cost more. You'd have to do the math for your situation, but insulation tends to cost quite a bit more than vapor barrier materials. And in an encapsulated crawl, you're only insulating the walls which should be less sqft than the floor. The vapor barrier covers most of the sqft of the space, and the super thick, fancy ones cost about $0.35/sqft. Closed cell foam costs $1 or more per board foot, and you'd be doing a couple of board feet per sqft to achieve the thickness you want. You'd have to cover the underside of the floor boards (total sqft of the crawl) plus the cost of the two vertical faces of each joist and the sill plates.

This article is pretty informative: http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

The part that applies most to your question is probably: "According to researchers who conducted a careful study of vented and unvented crawl spaces in North Carolina, homes with sealed crawl spaces with insulated foundation walls use 18% less energy for heating and cooling than identical homes with vented crawl spaces with insulation between the floor joists."

Unfortunately, the link to that specific study is broken, but it's a good read on the subject from a good source.

We typically do HVAC in attics in this part of the world. Foam is very different than bats between the floor joists as I have now. It as never frozen under the house and I seriously doubt it would with foam insulation on the floor above. If it were close a couple of light bulbs would fix it. Our lows here are in the 20's a few times a year. I have seen 9 once in 63 years.