I'm remodeling our basement and plain to insulate it since there is currently no insulation in there. The house is a ranch with a walkout basement with about 1/3 of the basement exposed. I had two options on insulating it, 1) put up 2" of XPS sheeting to the rim joist then have the rim joist spray foamed 3". 2) Spray foam the entire wall with 3" of closed cell foam.

If I did the XPS I would put my 2x4 wall up after the sheets are up and hold it right next to the XPS. The spray foam whole wall I would hold the 2x4 wall 1/2" off of the poured foundation so that the spray foam can get behind the studs and help with thermal bridging.

I will be getting quotes for the spray foam this Friday and have priced out the cost for me to do the XPS install. Its gonna come down to $$ but given my two choices will I see a noticeable difference between one or the other? I have no water issues currently with the basement but my only fears would be if there would be any reason to get to the foundation from the inside the spray foam would be a hassle.

The house is in South West Ohio.

Thanks

I think the spray foam is a better solution, but it will probably cost more. I'd hold the 2x4's 1" or 2" off the concrete; if you spray 3" the foam will overlap onto the studs, then you can fill the studs with batt insulation. If you use the sheet foam, foam the bottom of the sheet to the floor to prevent air from getting behind the sheet, and tape the sheets together. Chances of needing to get to the concrete is minimal - I wouldn't worry about it.

I think as far as cost goes if the spray foam is close to half the cost for me to do the XPS sheeting I will go Spray. If it's more than half I will need to think about it more.

If I do the XPS I planned to tape all seams, caulk the bottom AND top. I wasn't sure though if I did the XPS if I should take it all the way to the rim joist and butt it to it tight or leave an 1" gap so that the spray foam could get in between the two to help stop any air from coming down from my attic and possibly getting in behind the XPS?

I have read some conflicting reports about putting in fiberglass in the cavity for basements? I was originally going to do the XPS then fill the studs with fiberglass but reports of mold growing got me thinking of just doing the two methods above.

don't use fiberglass if there is any chance of it getting wet or damp, but Roxul batts shoudl work fine.

Bob, other than cost will I see much of a difference as far as comfort between the two methods?

I know the spray foam at 3" will have a higher R value but will it be noticeable?

When I thought about using the batt type insulation with the XPS I was going to hold it off the floor about a foot or so. Like I said before we have never had any issue with water getting into the basement but anything can happen.

I've been doing 2" of CCSF (closed cell spray foam) and adding 4"or 6" of batt insulation in basements for a while with great results. I suspect that if done well you'll have the same oiutcome with sheet foam.

Even at 2" the spray foam has a net lifecycle greenhouse gas footprint than the energy use it's offsetting, unless you go out of your way to find a vendor with water-blown 2lb foam or one of the newer low global warming potential (GWP) blowing agents (Honeywall Solstice, DuPont FEA-1000). Most foam is still blown with HFC245fa, which has more than 1000x the GWP of C02. An inch is more than sufficient for ground moisture protection and dew point control with a 2x4 studwall & rock wool or high-density fiberglass batts on the interior side of the foam in your climate.

XPS is usually blown with HFC134a, which runs about 1400x the GWP of CO2. An inch of ship-lap XPS sheathing with the seams taped or sealed with mastic would be sufficient there too.

The framing fraction of non-structural basement studwalls are low, since they don't need doubled top plates and aren't carrying the window & door loads. At 24" o.c. spacing and R15 Roxul you'd get pretty close to R11 for the studwall, plus the R5-R7 for the foam, for a net R16-16 which is a VERY reasonable level for a SW OH retrofit. There's little rationale for going higher than that unless you have Net Zero Energy or PassiveHouse performance goals in mind. See the recommendations for foundation insulation in table 2, p10 of this document (and read the whole first chapter.):

http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones

Dana, I have started to read that link and came across a topic I just had with a guy who is coming out to give me a quote. We were discussing the two options that I had came up with and he thought 1) the cost for me to do my whole basement with 3" CCSF was going to be pretty high ($2.35/inch/sqf) and instead do 1" CCSF then do blown in cellulose insulation once the sheet rock is installed. That was mentioned in your link but I'm a little skeptical to use the cellulose due to the mess and/or dust it creates when it gets exposed not to mention if it gets wet.

Since the basement currently has NO insulation in it any would be better than what I currently have. I guess I'm trying to find that balance point between cost and comfort.

Never use cellulose in a below-grade application that has even the remotest flooding possibility. People do it, but I wouldn't- you can get comparable performance at lower risk with rock wool batts, if you take the time to install them carefully.

Build a studwall 1" out from the concrete with the bottom plate resting on 1/2-1" XPS or EPS as a thermal and capillary break to keep the plate from taking on water. Drill through the bottom plate & foam into the slab to secure the bottom plate with TapCons or similar.

The foam installer can then "picture frame" shooting the perimeter of the framing to fill in the inch behind the wood prior to the flash-inch at center cavity. The resulting foam back-wall of the cavity will be smooth enough that you can insulate with either rock wool (preferred, for it's non-moisture wicking characteristics) or unfaced fiberglass batts (distant second.) Roxul sells R15 rock wool batts through both Lowes & Home Depot these days. It's substantially more expensive than the long-roll kraft faced R13 loss-leaders, but it's definitely a better product too, and a LOT cheaper than another 1.5-2" of closed cell spray foam.

With an inch of foam between the rock wool and the concrete you neither need nor want a kraft facer or an interior side vapor barrier- the foam keeps the rock wool warm enough to prevent copious wintertime condensation from occurring, and keeping the interior relatively vapor open to water vapor (but air-tight from a convection point of view) gives the studs a path to rapid drying. The colder your climate, the more foam you'd need, but in your location with R6 foam and R15 rock wool you have plenty of dew point margin, no need to go any higher-R on the foam.

When installing batts it's important to do ALL of the detailing right- even the pros screw it up regularly (which is why performance builders really despise batts.) Trim & sculpt carefully around electrical boxes etc, split the batt to fit around wiring or plumbing in the studs. First push/tuck the corners and edges of the batt into the cavity then tug it out fluffing it just proud of the stud edge, to guarantee a complete fill, no voids. Rock wool trims pretty easily & cleanly with bread knife, though there are also purpose-made batt trimming knives out there. I find it easier to deal with than fiberglass. YMMV.

An alternative would be to dense pack new-school fiberglass (L77, Optima, Spider, etc) behind netting to 1.8lb density before putting up the gypsum, but that's usually a pricey option too, and it wicks moisture more readily than rock wool.

3" CCSF was going to be pretty high ($2.35/inch/sqf)

That seems VERY high. Even do-it yourself kits run about half that and it should be even less for a pro sprayer.

Posted By ICFHybrid on 11 Mar 2013 06:30 PM

3" CCSF was going to be pretty high ($2.35/inch/sqf)

That seems VERY high. Even do-it yourself kits run about half that and it should be even less for a pro sprayer.

It's been running about a buck an inch per square foot in my neighborhood- maybe a buck-twentyfive for small jobs like a band-joist seal. 

Somehow I had  first read that as 3" @ $2.35foot, which seemed positively CHEAP. But 3x cheap = wicked expensive.  If it's that costly, use rigid polyiso instead- performance is about the same inch for inch. (I have 3" of reclaimed roofing iso on my basement walls, and it was cheaper than batts.)

Unless I read it wrong I thought your link suggested using cellulose in front of a spray in foam or foam board but maybe that was for above grade. We have only been in this house for 3yrs but have never had any water issues.

I'm gonna wait until I get all my quotes in and post back with their amounts and recommendations but it seems that I should do a hybrid of spray foam and Roxul or fiberglass over installing just the 2" XPS?

I thought that (phone) quote was high as well. The whole basement is 800sqf and I will only be insulating 3/4 of it due to my garage setup.

a hybrid of spray foam and Roxul

That is not a good combination for the installer, and it can't be ideal to leave an air space in there. Roxul is fairly firm and you end up having to trim it extensively to match the uneveness of the spray foam profile. Spray foam builds up in the corners between the studs and the exterior sheathing and I don't know how you avoid that. Blown-in blanket seems to be a good companion to the spray foam as it fills completely. Looks sorta cool, too.

ICF, what other blown in media besides cellulose are you talking about? Not those little round fiberglass disc??

Here are several trade names that are approved for the blown-in blanket system. I believe they are all various forms of short fiber fiberglass and are referred to as "blowing wool". The process of blowing them into the cavities behind an air permeable membrane seems to interlock the fibers. The packing and coverage is really quite impressive. I was unable to replicate the packing by hand on a few occasions that we had to remove some membrane to work in the wall after it was installed.

CertainTeed InsulSafe®SP or Optima®
Johns Manville Climate Pro® or SpiderTM
Knauf Perimeter PlusTM

Those aren't the only brands I ran across, just a few to sample.

Thanks I will check them out.

I have my first contractor coming out tomorrow and two more on Friday so I should know what this will cost soon. I am leaning towards the 2" XPS then Roxul in the stud cavity that way if there ever is a problem it will be easier to work on down the road.

Working on it wasn't difficult. Product performance (in terms of insulating my house) was WAY more important for me.

I disagree that Roxul can't fit well and would need substantial trimming to fit to a reasonably done flash-foam job. If the foam installer is a hack and leaves it wicked-lumpy, the spring factor of unfaced R19 fiberglass (yes, the industry's flea-bitten dog :-) ) compressed into a 2x4 cavity can accomodate a lot of surface irregularity, and performs at about R13 at that density & thickness.

While Optima & Spider et al are great products, the bang/buck for a below-grade app in a US zone 4/5 boundary climate isn't easy to rationalize. Before going there I'd be looking at reclaimed roofing foam and an all-foam solution, since it'll be both cheaper and better. (Two layers of 2" EPS or iso held in place with furring through-screwed to the foundation 24" o.c. would result in the same or better whole-wall R.) Call some commercial roofing contractors- many will have 2 & 3" foam culled from demolition and re-roofing available at a fraction of the virgin stock price. In my area there are multiple vendors whose primary business is used-foam. (Insulationdepot.com is just one, and will ship bulk order nationwide for a price, but local is usually cheaper for smaller quantities.)

Again, if using virgin stock foam, XPS would be a net-negative for the environment due to the blowing agents used, but either EPS & iso would be net positive. EPS & iso are usually cheaper per unit-R than XPS, but the R/inch is different. If using reclaimed foam, any type is good- the environmental hit is already taken, you're just extending the benefit side of the equation by re-using it.

Dana, I see your point on the whole eco side of this regarding the trade off's to the environment but the products are already made and available. I have been looking on Craigslist for a few months now looking for both rigid AND regular batt/roll insulation with no luck. I don't know what part of the country you are in but I have never seen nor heard of using board insulation on roofs until I started researching more into this basement for the stuff. If I can find it and its half the cost of new material by all means I will jump on it but as of right now it doesn't appear to be an option for this basement job.

Hopefully I will have all my quotes in hand by late Friday so I can post them and see which one/option would be the best bang for our $$.

Thanks

I disagree that Roxul can't fit well and would need substantial trimming to fit to a reasonably done flash-foam job

I find Roxul to be substantially more firm than R19 fiberglass. The industry standard fiberglass compresses in the bays much better to fit the irregularities, leaving Roxul as a more difficult product to install following spray foam. The biggest problem comes in small or irregular spaces where the fan nozzle causes deposition on studs or other structural members. That often requires custom cutting of the Roxul batts.

This can occur no matter how experienced your spray crew is. The only issues with blown-in in this regard is the occasional scraping of a stud face to remove cc foam overspray before stapling the fabric on.