Maybe this topic has been covered ,if so bear with me.
 I have a walkout basement under my home in the mountains of Western N.C
 The basement walls are 12" block changing to 8 inch block where my trusses sit. All poured solid. My 16 in open web trusses sit 0n 2x4 pressure treated. on top of the 12" with 8 inch block acting as rim board.  . Right now there is fibreglass packed into the openings between the trusses and the block walls. I figure I have  around 350 sq ft of rim  surface area here, 80 ft wall length x 30 ft wall widthx 16" hight.
 I feel that shooting the rim  areas between trusses and wall  with foam will give me a tighter house.
 Which would be best way to go and why? Should I buy a two part foam for around $1. 25 a board ft and do it my self? Spray maybe 1-2 inches of foam followed my the fiberglass backing? And should I use an open cell or closed cell foam.
 Not sure hiring someone willl be cheapest as the bid might be high due to the fact of small sq ft to shoot with all the cleanup.  There is a company out of Jax in Fl selling a two part foam they claim  costs around .7  to 1 dollar a board ft diy. 
 Ideas??

My company is in the process of completing a Spray Foam Trailer and I am looking for work for it. You buy the material and I will spray it at cost. I always prefer closed cell 2.5 lb foam it provides double or triple advantages over open cell for pennies more.
at 3 inches the material becomes strructural

buck3647
 Where are you located? I am just just south of Asheville N.d. And wouldn't an open cell be able to" breath" and help get ris of moisture if it gets in?

That should be Asheville N.C.

Doing it yourself with a kit doesn't take a rocket science degree, but there's an art to it. Most pros would do it for the same money or less if you have 1000bd-ft or more to shoot, and with the temperature controlled better equipment it's easier to get consistent results. (Take Buck up on his offer!)

2lb closed cell polyurethan foam "breathes" sufficiently to allow the wood to dry if you keep it to 2" or less which would give you ~ R13. The closed cell Icycene is lower R/inch, but you can put up to 4" in there safely (~R20). Buck would have to give us the spec for the 2.5lb goods, but it's typically higherR/inch, but also lower permeance (==lower drying capacity), and you may have to stop before 2" to keep it at about 1-perm, which is kind of a "sweet zone". Under 0.5perms you could be create some problems, but not so much at 1 perm. Open cell foams let far more wintertime moisture, which could be an issue if you're at altitude where it stays below freezing for weeks on end, but for most of NC open cell would be a viable option. For the minimal square footage and minimal R you're looking for, an inch or two of closed cell is probably worth it just to the vapor-diffusion range you're looking for. (You'd need about a foot of half-pound open cell to hit the right perm rating.)

Fiberglass batts stuffed on rim joists are just plain lousy any way you cut it. The underperform their rated R without a good-to-perfect interior air-barrier, and the air leakage creates a condensing convection loop on the cold rim joist & foundation sill when it's cold out, maximizing the moisture content of the wood. If the batts are unfaced they convect fast enough that the R-value drops rapidly with higher temperature differences, but it allows the rim joist to dry. If kraft faced it'll perform somewhat better thermally, but it'll trap moisture better too.

Dana1
Thanks, sounds like 2" of closed cell will best meet my needs. Then put the fiberglass back in?
I have not heard back from BUCK and his offer but if I do he will without a doubt get my attention. But his profile says he is in FL. and Asheville N.C. might be a bit far for him.

You can re-use the fiberglass, but make it snug, and use a permeable sort of interior air-barrier (like housewrap or heavy un-coated kraft paper) stapled tightly with no edge gaps. It's hard to make it perfect, and with the R of the foam it won't condense, but the better the air barrier, the more likely it is to perform to spec. If it has kraft or foil facer it's better strip the facer before re-using, since foil is a true vapor barrier, and asphalt coated kraft facers are designed to be <0.5 perms. Simply cutting slashes in the facer isn't adequate.

If the block isn't insulated, adding the fiberglass to the rim joist isn't going to cut the heating/cooling loads much, since the concrete-filled block has an R value of ~0.8. Insulating it with 1" XPS insulating sheathing + 2x3 or 2x4 studwall with un-faced batts can get you a decent R value at low mold risk & low cost. Glue the XPS to the block with pecan-sized blobs of foam board construction adhesive (that uses solvents that won't degrade the XPS), then build the studwall tight to the foam. Use sill gasket or strip of poly under the bottom plate of the studwall, and caulk the edges of the studs to the XPS for best performance on the fiberglass. With R13 batts + 1" XPS you'll be running ~ R17-R18 clear-wall R values, and the foundation will be able to give up ground/rain/dew wicking moisture to the room rather than rising to rot out the foundation sill, and won't condense/frost up during cold weather rotting out the studs. Use only un-faced batting, and depending on your actual climate use either standard latex (if your mean January temp is above 25F) or a vapor retardent latex primer (if your mean January temp is lower than 25F), to optimize overall drying capacity against the annual hours of condensation temps you get at the cold edge of the studs. If the block is unpainted, use a single coat of acrylic or silane masonry sealer prior to insulatoing to limit potential moisture wicking. The walls actively leak liquid water during seasonal downpours or spring runoff, or exhibit significant efflorescence, deal with exterior drainage issues first. For other, or higher-R options see: http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis (note the hygro-thermal simulations are for Minneapolis- you can be much more vapor permeable every where in NC, and there are benefits to keeping it between 1-2 perms total if your January binned hourly mean temps are higher than 25F, which they probably are.)

If you spray foam as a DIY with a 600 board-foot kit wait for warmer weather. Download the kit instructions, and monitor the temp of the tanks as you go along (see: http://www.tigerfoam.com/PDF-FILES/TF-OperatingInstructions.pdf ) Some people even put the tanks in a tub of tepid water on the warm-end of the operating scale to help keep the temps steady, since they otherwise they cool as the pressure is released during spraying. Both the chemical temps and sprayed surface temps want to be in the right range. Take it slow and steady- better to be a bit thinner than at first than overdoing it and running short. Even 1" is protective enough from a vapor transport point of view, and can seal well from an air infiltration aspect. If you have 350 square feet you can do it at ~1.5"+ with a single 600 board foot kit (theoretically you'll get 1.7" coverage, but shoot for 1.5"), and you'll be in the ~R10 range before putting up the batts.

Hey folks, dont want to highjack this thread but my situation is very similar and i am in western NC also. I have 14" web trusses set on a 2x10 treated that sits atop superior walls. They web trusses are banded by a rim board made of 1/2" treated plywood. The tyvek overlaps the the top of the superior wall by about an inch as does the hardie siding, which also has a 1/4 air gap between it and the tyvek. I have 100' of rim board and was wondering how this i can spray the DYI kits. Some spaces are so tight that adding batts properly after spraying would be difficult. The walls above are 6" sips so the rim board is my greatest weak spot of air infiltration. As always your advise is greatly appreciated Dana.

Posted By Brawler on 21 Feb 2011 09:04 AM
Hey folks, dont want to highjack this thread but my situation is very similar and i am in western NC also. I have 14" web trusses set on a 2x10 treated that sits atop superior walls. They web trusses are banded by a rim board made of 1/2" treated plywood. The tyvek overlaps the the top of the superior wall by about an inch as does the hardie siding, which also has a 1/4 air gap between it and the tyvek. I have 100' of rim board and was wondering how this i can spray the DYI kits. Some spaces are so tight that adding batts properly after spraying would be difficult. The walls above are 6" sips so the rim board is my greatest weak spot of air infiltration. As always your advise is greatly appreciated Dana.

With 1/4" of rainscreen gap between the Tyvek & Hardie the drying capacity of the rim board is greatly enhanced, which means you COULD go with thicker closed cell foam on the interior.  Unlike massive poured concrete, the Superior foundation wall has minimal wicking capacity up the concrete studs & facer, and unless you screw it up with a heavy vapor retarder on the interior it has ~1.5-2 perms of drying capacity toward the interior through it's 1" XPS.

If you have 100 linear feet of 14" rim board to seal and insulate, you could do 2 lifts of ~2" with a single 600 board-foot kit for ~R25, if you wanted to (adding a lot of structural strength to the rim board as well).  If you're careful you can probably do a ~1-1.5" shot over the whole thing (including the top of the 2x10 sill) using a 200 board-foot kit, for ~R6-10.   With 1.5"-2" of closed cell + a purpose-rated  sprayed fiber insulation (most wet-spray cellulose, or wet-sprayed JM Spider fiberglass, or some sprayed rock wools qualify at 3"+) as the interior ignition barrier would put you in the same R-value ballpark as your 6" SIPs.  You could just close in the walls & basement ceiling with 1/2" sheet rock to meet ignition barrier code on the spray foam, but more R wouldn't hurt.  A 3-4" shot of wet-sprayed cellulose blown-in-blanket over 2" of closed cell foam would be about right (5" of fiber if your SPF is only an inch.)

Mind you, the Superior system uses a bare-minimum R5 of XPS for the standard product, which is less than the R-value of even 1" of closed cell foam.  The combination of steel + concrete studs represent a huge thermal short, but it's broken by the R5 XPS, which makes the studs perform in some ways similar to a non foam-clad 2x6 wood studwall if you installed a cavity fill insulation.  (It's not identical though- the short through the fiber layer is much more severe.) If you have the bare-bones R5 version it's  probably worth insulating the foundation further with a blown fiber blown-in-blanket (Optima, Spider, or dry cellulose) or wet-spray (cellulose or Spider)  to at least 4-5" of depth after sealing & insulating the rim board.  If you insulated the cavities at the same time as you applied an ignition-barrier's worth to the rim-board foam it would cost less than doing them as separate jobs.  

With denser fiber the impact of the interior air-barrier on thermal performance isn't as much as with low-density fiber, but it's still there.  If a full cavity fill can be done with a sheet rock interior you could go dry-blown, and end up with an even higher R.  If I'm reading the dimensions of correctly a full cavity fill would be 7.5", which would put you in the ~ R30 center-cavity range even with low-density Spider or Optima or cellulose when combined with the 1" XPS.  (With the thermal shorts of the steel & concrete studs you're probably looking at ~ R26-28 for a clear-wall or whole-wall R, only slightly more than your SIPs.)  If you're EVER planning to finish off the basement as living space, it's probably worth it.  If there's even a remote chance of flooding, go with a rock wool or fiber glass blowing wool for cavity fill, not cellulose.  Steel & concrete studs and XPS could tolerate the water, but 7.5" of cellulose could take years to dry after a relatively modest flooding event.

Dana, thank you for the advise. Im' going to to just that, buy a 600bf closed cell kit and spray the rim. How thick could i spray without moisture problems? I was thinking of 4-5 inchs where i cannot batt. In some places i can add unfaced batts. Any problems with moisture putting thick unfaced batts over several inchs of spray? If you know of any reliable kits please let me know. Putting the tanks in warm water is a great idea, im gonna do that. The superior walls i ordered have 2 and 1/2 inchs of foam board on them. They were brand new when i bought them a couple years ago. Even though they meet code i would like to add more R value. What do you think is the safest and best bang for the buck. The basment is going to be finished. Dana, I can't tell you how helpful your comments have been over the past couple years. For me, trying to do everything i can myself, your help has been critical. Thanks Michael

Since you have a 1/4" rainscreen gap on the exterior enhancing drying capacity toward the exterior you can safely blast away as thick as you like with ccSPF on the interior, but do it in lifts no thicker than 2" at a time or you can run into issues. Since it's an thermal insulator undergoing a chemical reaction it can get smoking hot internally shortly after being applied if you go too thick in one shot, resulting in shrinkage & separation (sometimes days or even weeks) later. Some manufacturers suggest waiting 24 hours between lifts, but that's rarely done in practice. Breaking for lunch after the first 2" lift isn't a bad idea though.

In your climate as long as at least ~20-25% of the total R is foam applied to the rim board, interior batts present no special issues. (2" of ccSPF is R12 ish, so you have a lot of leeway with the interior fiber. I'll assume you're not going to R60 there. :-) ) With 2" or more of foam you can use kraft faced goods since kraft facers allow ~0.5 perms of drying, and there will be NO condensation in the fiber layer in your climate even if you stuffed R19 batts in there. If using kraft facers are easier than doing some other sort of air-barrier, make it as snug and air-tight as you can if you do. (It can be tough to detail around I-joists.) If unfaced, use Tyvek or similar, not poly or foil as the interior air barrier. Without an interior air barrier low density batts will only perform to about half it's rated R due to room air convection loops through the fiber.

With 2.5" of XPS on the foundation you're looking at a ~R12-R13 wall initially. Getting batts that fit snugly inside the steel studs without edge gaps could be tough, and blown fiber would be the right way to go. If it's a totally dry basement with good sub-slab drainage you can either dry blow cellulose in netting before putting up interior gypsum, or dry blow it after the gypsum, which would probably be the cheapest, or wet-spray cellulose before the sheet rock. (Dry blowing low density cellulose in stud bays behind wallboard is a reasonable DIY project with a rental blower.) If there's even a remote chance of flooding use rock wool or fiberglass instead. Even low density fiber would add ~R3.5/inch center-cavity to the stackup, but with concrete & steel studs shorting through the fiber the effect on the whole wall R would be more like ~R2/inch. Wet-spray would have the least sag issues over time, but even modest dense-packing of whatever goes in there may not be "worth it" since the ~3-5% performance hit you might see in 20 years won't add up to much since it's thermally broken on the exterior with the XPS. If you have at least 5.5" (2x6-ish) cavity to fill, you're nearly doubling the whole-wall R value. If 7.5", it may be slightly more than double. Either way you're cutting the heat loss about in half. And with ~50% of the total R in exterior foam the humidity cycling at the cold edge of the cellulose would be quite low, which minimizes how much it settles over time. Interior vapor retarders are neither necessary or desirable, but you needn't sweat the details as much with steel & concrete studs as you would with an interior wood studwall, since the facers on the gypsum would be the most susceptible material, but will always be at the interior temperature & humidity.

Dana, could you clarify a couple things for me please? You recomend kraft faced insulation. Is that strictly to prevent interior convection currents? The trusses will be sealed top and bottom. Would that eliminate the need for kraft faced batts? Do you know which brands are most reliable for 600bft diy spray kits. My basement walls will be drywalled and i plan on useing fiberglass insulation to fill the cavities. Should i use batts with or without kraft facing? After this week or so we will be closing in the walls and ceilings as soon as we pour the radiant on the middle floor. Finally feels like we are making progress! Again thanks for the help. Michael

Sorry to have left this hanging for more than a week, but no loss.

Yes, only use kraft faced goods if that's the easiest way to get an interior air-barrier. Kraft facers impede drying capacity a bit but you've insulated the exterior sufficiently that it won't need much drying capacity, as it won't be accumulating condenation moisture in winter. Any batt insulation has to have air-barriers snugged up to BOTH sides of it to perform at it's rate R. If it's not fulling filling a cavity, you need a facer of some sort no matter what, but it if does fully fill the cavity, the sheathing/wallboard/whatever is enough.

IIRC almost all 600bd.ft. kit vendors use the same chemical manufacturer as a source, and are pretty much equivalent. (They may use different tips & tubing, but they all look the same to me.)

Thank you Dana. I never really understood that but it now seems obvious. Im gonna order a 600 bf kit tommorow. Thanks again. I will let you know how it goes. Also, i just ordered a smoke pen and i am planning on doing a little blower door/air infiltration testing before and after i spray. Thanks Michael