Basement Spray Foam?
I am in the process of planning to finish the basement of my new (~2004) home in western Wisconsin. I've been doing a lot of reading on this forum and the Building Science Corporation and have learned enough to know that I need to learn more before making this investment.
My basement has a "lookout" wall on the north side with the rest of the walls being full height concrete. My neighborhood has sandy/gravelly soils but does have high groundwater which is normally about 2 feet below the slab. The builder did provide a sill gaskets and all sill plates are pressure treated.
For the floor, I'm going to do a test pit (I'm expanding the sump pit to fit a backup sump pump anyway) to see if there's insulation under the slab. If not, I'm going to go with vapor barrier, 1" XPS and 5/8" plywood or OSB. I'm also considering Delta-FL instead of the vapor barrier so that I'd be able to dry the slab without removing the entire floor (Tapcons and all) in the event that bulk water became an issue due to the high groundwater.
I'm far less sure about the walls. The builder installed a 2x4 stud wall around the perimeter of the basement held inside the concrete foundation by perhaps 1/2". He then installed fiberglass batt insulation and a vapor barrier (stapled to the face of the 2x4 stud wall). According to this forum and Building Science, this is not the recommended method. Instead, it it appears to me that best practices for a raw basement would have been 2" XPS or EPS board hard against the concrete with 2x4 stud walls set inside (with or without additional fiberglass batt insulation).
Unfortunately, I no longer have a raw basement so I am faced with two options: 1. Rip out the existing stud wall and replace with the best practices method mentioned above or 2. find an alternative that would allow me to leave the stud wall in place which leads me (finally) to my questions:
- Is spray foam a reasonable method to insulate below grade concrete walls? I can't find where it was discussed on this forum. Most literature that I've been able to find plays up the air tightness of the spay foam. I can't seem to find much information about vapor permeance. If so: Open cell or closed? What weight? What thickness?
- Is spray foam a reasonable method to insulate above grade exterior walls? I'm talking about the upper part of the lookout wall and the joist bays. If so: Open cell or closed? What weight? What thickness?
Thanks in advance for your replies!
Of course it is a good choice.
2lb. per cubic foot density
2"+ depending on your budget (thick enough that the inside surface is above the dew point on the coldest day of the year)
Open cell (1/2lb. density) foam is crap.
If you thought doing the walls with EPS or XPS was good, why wouldn't you think a monolithic layer of an ever higher performance foam was good?
The walls must be dry to apply the foam.
Some spray foam will not adhere unless the wall is relatively warm. A pro will know what temp is required for what they are spraying, but it is something to be aware of if you are considering DIY.
It's (almost) never a good idea to put a vapor barrier on a foundation wall, ESPECIALLY on the interior side of a studwall, which which will trap ground moisture next to the susceptible studs. If there is no space between the studwall and foundation to work with, you may have to move it out, but it's re-usable. Cold stud edges against concrete aren't gonna cut it, no matter what else you do for insulation & vapor retarders.
The cheapest reliable solution using a studwall is to use any type of closed cell foam against the foundation, either EPS (cheapest, but thickest), XPS, 2-lb polyurethane, or foil-faced iso if it's a relatively dry ground conditions and you have sill gaskets as a capillary break for the foundation. If you want to fatten out the R-value with a studwall, use UNFACED batts, and use the IRC-specified amount of R in the foam layer for the stud dimensions and your climate zone that works without an interior side air barrier:
Find your zone here:
Most of WI is in climate zone 6, so for a 2x4 wall with UNFACED R13-R15 batts (fiberglass or rock wool, but not cotton or cellulose in a below-grade application) you'd need a minimum of R7.5 to eliminate wintertime condensation issues. With 2" of EPS (R7.8, even for cheap low density Type-I EPS) you'd be there, and though the vapor retardency of EPS is relatively high, that's a GOOD thing for lowering the moisture content of the concrete by allowing it to dry toward the interior. This is protective of the foundation sill, and presents no hazard to the studs, as long as there are no strong interior side vapor retarders such as kraft/foil facers, poly sheeting, or vinyl/foil wallpapers. If you're in zone 7 bump that up to 2.5" if EPS, or go with either 2" XPS, or 2" of 2.lb spray polyurethane foam.
Half pound foam can sometimes work in these situations, but only if the soil conditions are consistently dry. It has more than 2x the vapor permeance of low-density EPS, and may not slow the foundation drying sufficiently to fully protect the paper facers of the wallboards, leading to mold conditions for the wallboard & studs.
Half pound foam is usually well over 10 perms even at R13.
Most 2lb foam is 0.8-1.2 perms @ R6, and ~0.5 perms @ R10-12
EPS is about 2-5 perms @ the recommended ~R8-10
XPS is about 0.4-0.8 perms at the recommended R7.5-R10
Foil faced iso is <0.1 perms, at any thickness.
Fiber faced roofing iso is typically 0.5-1 perms at any single-layered thickness.
If it's fairly damp ground that isn't amenable to correction by better bulk-water routing at the exterior, it's sometimes worth putting a dimple-board vapor barrier against the foundation first, which allows some drying of the foundation and drainage when the foundation is saturated. But you'd better be sure of your capillary break under the foundation sill, which may require jacking up the house a hair and shimming in some EPDM roofing membrane or something. (Sounds worse than it really is.)
If you have outlets that deal in reclaimed roofing foam (check the local craigslist materials section for "rigid insulation" too) it's usually cheaper to do the whole thing in rigid foam, held flat to the foundation with 1x furring through-screwed to the foundation with TapCons (you may have to order the longer TapCons online if you go more than 2.5" on the foam- box stores don't always carry them longer than 4" or so, and you need at least 3/4" penetration into the concrete.) Reclaimed roofing foam is typically 1/4-1/3 the price of virgin stock, and is cheaper per unit-R than unfaced R13 batts. (I did my own basement with reclaimed 3"/R18 fiber faced iso for about @ $2 per square foot, which includes the furring, TapCons, and half-inch gypsum.) If iso (polyisocyanurate) you have to keep the bottom edge an inch or so off the bottom unless you have your floor-XPS/EPS running all the way to the foundation wall, since on a potentially humid concrete it would slowly wick up water, unlike other foams with a more uniform closed-cell structure. (That's why it's always sold with vapor retardent facers.)
In any WI location it's worth taking it to at least R15 whole-wall (with the thermal bridging of studs & plates factored in), and you'd be there with IRC mandated R7.5 foam + R13 batts, or with 4" of EPS (any density/type), or 3" of iso.
Any foam-board solution needs to be sealed at the seams. If you have a lot of it to do you might spring for a 12 board-foot FrothPak (at box stores), which can seal more than a case of Great Stuff or similar.
Lower temperatures are more of a concern for your yield (liquid to foam), not adhesion.
Originally Posted by cacher_chick
Adhesion is similar to most applications, you need a clean, dry, oil-free, well fastened substrate.
Foam can be applied at temperatures near freezing, the substrate temp is important for creating a good cell structure in your foam.
Professionals have access to different formulations (more catalyst for colder temps), proper heating equipment for the raw materials (very important), and proper application pressure. None of these things are guaranteed if you DIY.
The hose itself is heated when you hire someone to apply these products, temperature of the raw liquid is 1000x more important than substrate temp.
Having once designed hose-heater controls for spray foam equipment during my tenure as an electrical engineer, I can vouch for how important getting both the A & B side temperatures dialed is for optimizing results.
DIY kits can do at best "OK", and work best if you keep the tanks in tub of warmed water when applying it, but it's nowhere near as consistent as digitally controlled heaters in the hoses keeping the temp of both chemicals entering the mixer in the gun perfectly stable & optimal for the conditions.
I'd never even CONSIDER doing a whole basement wall with DIY kits, but I might do a section of band-joist or something if the job was too tiny (~600 board-feet or less- about one kit's-worth.) I wouldn't wait until it's cooled off to 10F outside to start though. :-)
Thanks for all of the replies!
I have a few follow up questions:
1. Would 2 lbs closed cell spray foam to a thickness of 4" in the bays and 1/2" behind the studs provide sufficient R-value below grade in Zone 6?
2. Would 2 lbs closed cell spray foam to a thickness of 4" in the bays and 1/2" behind the studs provide sufficient permeability to allow the concrete to dry to the interior?
If the answer is no to either of those, it appears that my only option would be to pull the stud walls away from the foundation. Correct?
3. Would 2 lbs closed cell spray foam to a thickness of 2" in the bays + 3.5" FACED fiberglass batts provide sufficient R-Value above grade (2x6 framing) in Zone 6?
For the record, I'd never even consider trying DIY spray foam of this magnitude and I won't be tackling the construction until next summer.
I think if you have lots of hydrostatic pressure pushing moisture inside, you might need a system to take care of that...
4" of foam wont allow much permeability at all, don't expect to dry to the inside.
You don't want to sandwich your wall cavity with vapor retarders, so please don't use any faced batts at all.
Are the stud walls in great shape in the first place? Is there sill gasket or pressure treated sill plate?
dlarrivee, Thanks for the replies. But they illustrate my point of confusion. In your first reply, you said spray foam is a good choice. In the second, you've said it won't allow drying to the inside. To be fair, you were answering two different questions, but there's apparently a tipping point between 2" and 4" where spray foam becomes unacceptable for use in a basement. Its that tipping point that I'd like to understand better.
The stud walls are in great shape. Interior stud walls have pressure treated bottom plate but no gasket. Exterior walls have a sill gasket and pressure treated sill plate.
To be clear, the faced bats question was about the above grade lookout wall (2x6 framing), not the below grade concrete wall. Still might be a bad idea, but just wanted to be clear with the background to my question.
I also said you might need to implement a system to take care of the water prior to spray foaming.
Interior french drain, etc.
The half-inch of foam between the stud edge and concrete would run about 2-2.5 perms and about R3, which would be sufficient R to avoid wintertime moisture loading for the above grade section and a (just barely) sufficient capillary break/vapor retarder to limit ground moisture loading. Ideally you'd want an inch of foam between the stud edge and concrete, but as long as you have at least 1.5" center cavity above grade you won't have a condensation issue. But 4" of foam expensive, and it reduces the inward drying capacity of the below grade section to under 0.3 perms.
Originally Posted by Schopsy
A 2" shot of cc foam that filled in the half-inch behind the studs combined with compressing R13 batts into the ~2.5-3" nominal space it would also be just fine, and have nearly the same whole-wall-R. (The thermal bridging of the studs pretty much wastes the high-R of the closed cell foam, since wood has more than 5x the thermal conductivity of the foam.) The drying capacity of the below grade section is now about half a perm or more, which is good enough. If the installer is a real artist with a spray gun, you could even do 2" for the above grade section, tapering to 1" at the bottom and it would work GREAT! That's better drying capacity for the foundation, and very decent dew-point control for the colder above grade part.
The greenhouse gas potential of the HFC blowing agents used in the 2" of foam that you DIDN'T use is greater than 50 years of the energy use it would have offset even without the fiberglass, and more than 100 years if you compared it to keeping 2.5-3" of fiberglass. Closed cell polyurethane foam is great for air sealing and moisture control, but in high-R applications it goes net-negative quickly on lifecycle-environmental issues.
Newer lower impact blowing agents are currently under development, but not yet on the market. They also have no track record, and it's a somewhat touchy chemistry with a history of long term shrinkage issues when things get tweaked. Most of those other issues have been nulled out for HFC245fa blown foam now, but it has more than 1000x the greenhouse potential of CO2, which is why there has been pressure on the industry pressure to change blowing agents. (HFC245fa was a HUGE improvement over the ozone-eating and greenhouse issues of prior HCFC blowing agents previously used, but it's proven to be no real panacea.)
NEVER (and I really mean never!) use facers of any type on fiber insulation in a below grade studwall. With 2" of foam above grade and a compressed R13 batt on the interior side more than half of the R is on inside the "condensing surface", or interior face of the foam. There will never be enough condensation on that surface to bead up into liquid drops, even on the coldest day of the winter, as long as there is some sort of interior-side air barrier (like wallboard.)
Assuming the interior air's dew point is between 35-40F (typical for a zone-6 mid-winter, unless you're running a sauna down there or actively humidifying to something over 35%RH @ 70F), you don't even get the first hint of adsorbed haze on the foam until it's below 10F outside, and it would have to be continuously below 10F outside (even for the daily highs) for WEEKS before enough moisture would accumulate via vapor diffusion through latex paint on gypsum to form droplets capable of dribbling down. (And when they got to the warmer sub-grade section they'd evaporate anyway.)
But if you put a facer on the interior side you have a classic moisture trap, with very low drying capacity on the exterior- it can only dry outwardly through the 2" of foam on the above grade section, and not at all on the below grade section, and the 2" of foam would run ~ 0.5-0.6 perms. On the interior side with a kraft facer you'd have more surface area to dry through, but at only about 0.4 perms. With latex paint you have 2-3 perms, more than 5x the drying capacity, and even in the event of the occasional or one-off bulk-water intrusion it could still dry fast enough that the studs would not be compromised. Going without facers makes it FAR more resilient.
It's an itchy process, but there's no rocket science or huge time investment required to strip the facers off the existing fiberglass batts then friction-fit them back into the cavities for a compression-fit behind fresh wallboard after you've foamed the wall. It'll still be running about R12 @ 3", R10 @ 2.5". Compressing mid-density R13 batts increases the R per inch to about R4/inch when squished to 2.5" thickness rather than the full-loft 3.5", which still decent performance.
Thanks for the detailed replies! I wanted to verify the configurations:
Below grade (2x4 studwall set 1/2" inside concrete foundation): 2" thick, 2 lbs closed cell spray foam + 2" thick compressed UNFACED fiberglass batts + gypsum wallboard
Above grade (2x6 lookout wall): 2" thick, 2 lbs closed cell spray foam + 3.5" thick uncompressed UNFACED fiberglass batts + gypsum wallboard.
In my "basement", the foundation wall is only 44" above the slab and then there is a small stud wall on top of that, grade is about waist level.
I framed a full height (slab to floor joist), stud wall, in front of the foundation wall (1" off).
I sprayed 2" of foam below grade, and 3" above, filled the remaining void with fibreglass.
I'm a certified applicator and I've done 2" and 3" on foundation walls depending on geography and other variables.
Those stackups will work GREAT in your climate, with plenty of margin on dew point control, and low risk of ground moisture issues with below-grade stud edges.
Originally Posted by Schopsy
The weakest point is having only a half-inch between the stud & concrete, but if care is taken that it's well-filled with 2lb foam without gaps there won't be problem.
A good applicator will "picture-frame" each stud bay before filling it in.
Essentially pointing the gun into that corner where the 1/2" gap would be to round the harsher corner before his first lift of foam is applied.