I would think he would use EPS foam.

We start air sealing when we start building, so much easier and more effective, but sounds like you are past that point. Usually the insulator will caulk all gaps and cracks on the drywall face of the wall including top plates, bottom plate to floor and shoulder/king studs, other double/triple studs, ect. A good start but blower door testing will show plenty of other opportunity.

We (builder) do a more comprehensive air seal beyond what our insulators do, if yours is unfamiliar then you would bring in a home performance contractor or your insulator. We do our air sealing during construction then after framing before wiring is in, then we do another pass after mechanicals/wiring/plumbing are in. Typically adds maybe $1500-2500 to the clients bill. I air seal every stud bay except for bay to bay holes except for exterior to interior bay connections, those get sealed. Here's where it gets tricky, we blow the walls and hang the flat ceilings and fire walls. Then we air seal the attic(s} and then blower door test (carefully, it can pull the poly off) with the poly on and find any last leaks, then the drywaller gets the ok to finish hanging and the insulator blows the attics. The drywaller and insulator will not like this arrangement too much but thats the way it is if they want the work. It helps that the same company does our new home drywall and insulation work, much easier to coordinate and get away with how we do it. I do BIBS walls and cellulose attics with this arrangement, would like to spec netted dense pack walls but they dont have the experience to do it.

I would also recommend spray foam in the basement sill, make sure they also spray the mudsill to the foundation. In tight homes the sill box gets pretty wet in the winter, in several remodels of newer homes when cutting through the rim we've found deterioration of the OSB rim board. Generally we spray the sills, we're just more careful to do it right, then we have the insulators add an R19 batt, then they come back and redo it because they didn't fit the batts well enough. Then the workers get yelled at in spanish.

You can spec all the right moves but it doesn't do you much good if it's hasty or done wrong, I'm fortunate to work with some good people who understand the "why" and have pride in the work, that's what you need to look for. It's not going to do you much good to print this thread and put it in your builders hands, he's obviously not getting it.

Posted By Sturgeon on 05 Dec 2011 08:05 PM
ok an update: I have a stucco contractor who is able to do exterior foam with true hard coat stucco. He uses the Sto powerwall system. There will be a rain screen for drainage as well. The wall layout is (inside to outside): plywood, tyvek stucco, #15 felt paper, 1/4" drainscreen, 1.5" blue or pink rigid foam (i assume this is XPS, as it is R 7.5, but haven't confirmed this), 3/8" casing bit on all edges ending on building, fiberglass mesh, 3 coat hard stucco, and an elastomeric waterproof coat over the top. He said that this wall system will be R9 (7.5 from the foam, + 1.5 from the stucco system). Pricing is expensive, but i really like the rainscreen, waterproof finish, and idea of exterior envelope insulation to address heat loss through the studs. I will probably use less expensive insulation now within the wall cavity-- likely dense pack or wet-spray cellulose. up to R20 (2x6 wall). This is better than fiberglass batts for my purposes, correct? How do I air-seal if i'm just using cellulose in the wall cavity? Does the 1.5" of rigid foam on the outside & elastomeric finish provide sufficient air sealing & protect against air infiltration? If not, how do I properly air seal and who normally does it? The builder said he will get some canned spray foam & seal cracks/gaps, but I'm not sure how thorough this will be. One other question is on the foundation-- I did R10 insulation on the outside of the foundation & also underslab insulation ( don't recall the R value off the top of my head for the underslab insulation). We eventually want to finish the basement. Several insulation contractors recommended spray foam inside the basement to guard against moisture & insulate. Is it unreasonable to just put in batts since I have exterior R10 insulation? Thanks!

Pink/blue board is indeed XPS, and at 1.5" will run about 0.8-0.9 perms.  It's not an air barrier unless detailed as an air barrier.  With a 6mm rainscreen between the stucco & foam, the elastomeric weatherproofing on the exterior can't function as a primary air barrier. 

Air sealing the structural sheathing can be done with combinations of mastic/spray foam/caulk, and taping & foaming the XPS to make it air-tight also helps.  The Tyvek can also be detailed as an air barrier (but rarely is.)  I prefer treating the sheathing as the primary air barrier because it is harder to damage/degrade over time.   Caulking the interior of the stud bays to the sheathing addresses it part-way (and is still worth doing) but it doesn't air-seal the studwall plates to the floor, etc., whereas air-sealing the sheathing from the exterior covers it all.

Blown/sprayed celluose has far fewer voids & compressions than any batt solution, and it buffers seasonal humidity.  Cellulose at 3lbs+ density will also tighten a wall that doesn't have a defined primary air barrier, but when you have a choice it's always better to air-seal prior to insulating.

With R10 on the exterior of the foundation wall you can get away a studwall solution, but don't put the wood in direct contact with the foundation wall where it can wick moisture.  Even a half-inch of unfaced XPS or unfaced EPS between the studwall and concrete provides an excellent relatively vapor-open (>2 perms) capillary break through which any ground moisture wicking up from the footing can then dry toward the interior.  Use only unfaced fiber in the stud bays, and no interior vapor retarders, or you may be trapping ground moisuture inside the studwall (latex paint is OK, foil wallpaper is not.)  Be sure to put foam  (even a good sill sill gasket) under the bottom plate too. 

A shot of 1-2" of closed cell foam to insulate the band joist & sill, making it air-tight to the top of your interior studwall works, and still allows some inward drying capacity. You can then blow cellulose to fatten out the R at the band joist. If using batts there instead of blown it still needs to be compression & gap free, and have a semi-vapor-permeable interior air-barrier (not a kraft or foil facer) to retain thermal performance without impeding drying.

Update: Due to cost, we were unable to go with exterior foam. wall set up is: 3 coat stucco, 15# felt paper, stucco wrap, 1/2" plywood, & 2x6 studs. Insulation specs: exterior walls: 2" closed cell spray foam, followed by 3.5 " blown in cellulose, 4" closed cell at rim joists, 3" open cell sprayed over 2nd floor ceiling, followed by blown in cellulose for R60 roof. We have R10 Rigid foam on exterior of basement walls & under slab. We will use R13 unfaced batts for interior of basement. We will be doing a smoke pencil blower door to detect any leaks after our initial air sealing. Who has done this & does Anyone have advice for this & it's timing? Presently, we are planning to do this after spray foam is in & all caulking is done, prior to cellulose. Insulation contractor is to seal any leaks found. Any tips for complete air-sealing are appreciated. After drywall etc, there also will be a formal blower door test done.

The idea of doing a blower door test when you can still get at things to seal them up is a good approach. It was not possible to do that on my house because of the order and type of construction. In this case, the wall and ceiling sheetrocking were done at the same point in the construction process, and that required that the walls were already filled with cellulose. Without the ceiling sheetrock being completed, the vented attic would just allow large amounts of airlfow into the house. I bought some plastic to try to seal the ridge vent and the vents in the eaves, which probably would not have worked too well, but as it turned out, we could not get the blower door test performed within the construction schedule until everything was completed.

Hope that you have better luck with your house, but do consider the "sealing" state of the house when you want to do the tests.

On the basement wall XPS or unfaced EPS between the studwall & studs is probably closer to best-practices. To for the batts to not lose effective-R to convection currents you can't leave a gap between the batt and the concrete, but the capillary draw of the concrete and the wicking capacity of the fiber means you don't really want the concrete & batts to touch. A semi-permeable non-wicking material like XPS or EPS can fill the gap and provide a non-wicking air-barrier to the cold side of the stud bays.

An alternative would be to leave 1/4-1/2" of space between the concrete & studs and fill it with open cell foam.