So my plan is to seal up my crawl space, 1500 sq ft home with a block crawl space under 3/4 of the home. I have the ductwork in there and it is vented. I was going to have spray foam under the entire floor but I'd eventually like to change out our electric heat pump with a more efficient one and put that in the crawl space. This would free up floor space in our already small basement. I am located in SW Missouri. There are no moisture issues under the house and aside from a few small mice I sent to Valhalla and typical spiders, crickets, etc, its a rather uneventful place. I've read a lot of other threads on how beneficial it is to seal up the crawl space, but I get a bit lost on the methods. For the record we don't have termites or carpenter ants and never have (that I know of). Never found any evidence of them. I want to be able to inspect the foundation periodically however so I must keep that in mind. All around the interior of the crawl space is a metal termite strip that's been there since construction so I want to keep that in place. SO, is this plan correct or am I missing something? 1) spray foam in between floor joists with open cell. 2) spray foam foundation block walls down to floor with open cell. 3) Install liner on floor and up 2 feet on the sides. 4). Nail liner to top plate down over floor liner and use mastic tape to join the two. For the record I don't plan on doing this myself but I want to make sure I know the best plan so I'm not talked into something by a local contractor. Thank you in advance for your help.

Be sure to check the building codes, especially if you have a furnace in the crawl space, to make sure that you do not need a fire barrier over the spray foam that you are planning on adding.

Going un-vented then insulating the floor & walls of the crawlspace rather than between the joists is probably cheaper (and definitely more inspectable) than insulating between the joists, and it puts all the ductwork inside of conditioned space. For your climate about R10-R12 on the crawlspace walls and R8-R10 on the crawlspace floor is enough. Even if the ducts were elsewhere inside of conditioned space, getting to the same energy use performance with a joist-insulation solution would take more than R30 in foam between joists. (See table 2, p10: http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones SW MO is in climate zone 4.)

Foam the band joist and foundation sill right down to the floor/bottom of the crawlspace with 2" of closed cell foam, and block off the vents. Alternatively 2.5-3" of rigid EPS on the walls works (2 layers with seams staggerd about 1' works, seams sealed with mastic, can-foam or FrothPak.)

For crawlspace floor insulation 1.5-2" of rigid EPS above or below your vapor barrier works for your climate zone. If you an ignition barrier you can put a 1.5-2" non-structural "rat-slab" on top of the EPS. (If you insulated the walls with rigid EPS it would be cheaper than with closed cell foam, and would take 2.5-3")

If you insulate the crawlspace walls without closing up the vents you would still have all the summertime moisture getting in there, and with open cell foam between the joists moisture could collect on the sub-floor during high humidity high air-conditioning periods. The thermal bridging of the joists means the exposed joist edges would also run colder than the outdoor dew point in summer, putting them as mold/rot risk too. If you close the vents and insulate the walls with closed cell foam it isolates the crawlspace from the outdoor environment and instead couples it to the interior- the temperature & moisture in the crawlspace air will track that of the rooms above, which means the wood all stays drier.

By putting the ducts inside the pressure boundary of the house duct leakage is of less consequence, and you would only have to insulate the supply ducts, not the returns.

The metal termite shield is a thermal bridge, but in your location the energy consequences of leaving it are very low, especially in comparison to the cost of a potential undetected termite-infestation- leaving it is the right thing to do. You could also do the walls rigid-foam, leaving a 3" termite inspection gap (required by code in some areas) which is also a thermal gap, but of comparatively low energy consequence in your area. See figure 3-14 in this document:

http://www.ornl.gov/sci/buildingsfoundations/handbook/section3-2.shtml

more on crawlspace treatment:

http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

http://www.buildingscience.com/documents/information-sheets/crawlspace-insulation/files/bscinfo_512_crawlspace_edit.pdf

More on ducts in/out of conditioned space:

http://www.buildingscience.com/documents/reports/rr-0305-why-it-s-so-important-and-troubling-to-keep-ducts-and-equipment-in-conditioned-space

http://www.buildingscience.com/documents/information-sheets/information-sheet-ducts-in-conditioned-space/files/bscinfo_602_ducts_conditioned.pdf

Well, thankfully I live out in the county where building codes consist of "we require your building have a roof" and that's about it, literally. Lol. I could cut corners but I make every attempt to he safe and do things right, if I need a fire barrier then ill put one in, code or not. Thankmyoumfor the advice.

Dana, thank you for taking the time to reply. I've read quite a few of your replies on the site and appreciate your feedback. I would prefer to do this myself so I can buy the supplies along the way and make sure everything is tight and right. I don't imagine it can be that difficult to liquid nail foam board to concrete block and tape it off. So after reading your reply, reviewing your links, etc, my mind exploded. Lol. Ill start off first with my modified plan after reading your reply. 1). Use 2 layers of rigid foam board with staggered seams from the floor to a couple inches below the termite shield. Liquid nail the foam to the block walls and mastic tape every seam. The floor creates a problem, its slightly uneven and filled with pea gravel. If there is a vapor barrier or any kind I cannot find it. It may be down further then the 5 or so inches I dug but I suspect the house, being 23 years old just doesn't have one. I assume the floor insulation you're talking about is not something I can get at lowes/home depot as everything they sell would be a broken and cracked mess the first time I crawl in the crawl space. I'm sure I can find a liner to go down for vapor though. You may have addressed this and I just missed or misunderstood this, but if I purchased a spray foam kit, I can use that for the space in between the floor joists above the block wall they rest on without fear of rot/mold in that location correct? Rather then ramble on ill stop there. I will take some pics of my crawl space so you or anyone else looking can see what I am referring too. Thank you again for taking the time to reply.

Posted By rykertest on 06 Feb 2013 10:05 AM
Dana, thank you for taking the time to reply. I've read quite a few of your replies on the site and appreciate your feedback. I would prefer to do this myself so I can buy the supplies along the way and make sure everything is tight and right. I don't imagine it can be that difficult to liquid nail foam board to concrete block and tape it off. So after reading your reply, reviewing your links, etc, my mind exploded. Lol. Ill start off first with my modified plan after reading your reply. 1). Use 2 layers of rigid foam board with staggered seams from the floor to a couple inches below the termite shield. Liquid nail the foam to the block walls and mastic tape every seam. The floor creates a problem, its slightly uneven and filled with pea gravel. If there is a vapor barrier or any kind I cannot find it. It may be down further then the 5 or so inches I dug but I suspect the house, being 23 years old just doesn't have one. I assume the floor insulation you're talking about is not something I can get at lowes/home depot as everything they sell would be a broken and cracked mess the first time I crawl in the crawl space. I'm sure I can find a liner to go down for vapor though. You may have addressed this and I just missed or misunderstood this, but if I purchased a spray foam kit, I can use that for the space in between the floor joists above the block wall they rest on without fear of rot/mold in that location correct? Rather then ramble on ill stop there. I will take some pics of my crawl space so you or anyone else looking can see what I am referring too. Thank you again for taking the time to reply.

The solvents in standard construction adhesives will eat into polystyrene and polyisocyanurate. Use specially formulated foam-board construction adhesive (available at box-store home centers from a couple of different manufacturers.)

In addition to the adhesive you'll need to install furring/strapping through-screwed to the foundation with TapCons 24" o.c. for a reliable long term bond, and that would give you something to hang gypsum on, should you be required to install an ignition barrier.

Level up the pea-gravel as best you can- it doesn't need to be dead-level, since rigid foam is at least somewhat flexible. If you think even poly-faced EPS (available at box stores) is going to be too brittle to accomodate the uneven floor, use 3/4" or 1"  XPS (pink, blue, green, whatever, also available at box stores), and put down two layers, both layers taped.

At a minimum 6-mil polyethylene sheeting would work, but 10-mil or 20 poly sheeting will hold up better. Lapping the seams by a foot and sealing them with duct-mastic &/or housewrap tape works.

I believe what you're referring to by  "... the space in between the floor joists above the block wall they rest on..." is the foundation sill & band/rim joist.  (See: http://hostedmedia.reimanpub.com/TF...HBL_08.jpg ) Yes, foaming that with closed cell foam is a perfectly fine way to insulate that, but it's probably going to be more foam than you get out of a 600board-foot TigerFoam/Fomo-Foam kit to hit R10 (1.5") to do the whole perimeter, sealing it to the top of the  rigid wall-foam.  For 2x10 joists with a bit of ledge for the sill and top of the wall-foam you're talking about 1.5-2 board-feet per foot of perimeter distance.  The kits run about $1.25/board-foot plus protective suits/goggle/masks, do a DIY would be running about $2/running foot of perimeter distance or a little bit more.  At more than 1000 board feet it's usually cheaper to hire a pro.  In your climate you can use either closed cell or open cell foam on band joists, and 3" of open cell foam would usually cost about $1.25 per foot of perimeter length, and deliver about R10 or better performance, making it a better value than kit-foam. But get quotes- small jobs often get bid higher since it ties up the equipment for the same amount of road-time whether it's a 500 board-foot job or a 5000 board foot job, with the same set-up and break-down time/cost.  (It depends a bit on how hungry they are for work, which varies a lot by the local construction economy and the number of contractors competing for the business.)

Good feedback. Thank you for the help. Ill start getting bids from contractors and seeing what the damage will be.

Well after getting my ducks in a row, it doesn't look like insulating and sealing off my crawlspace is affordable. I was flabbergasted at what my small crawlspace cost just to get a liner put in. A liner and a pump (which I have no water issue so why I need a pump I don't get) was $4500!!! That doesn't even include foam board insulation on the walls which was another grand. Thank you for the help Dana, I'm sorry I couldn't put it to use.