I'm building a new home and the builder/framer/lumber company screwed things up. The plans for the house called for 2x6 exterior walls with R19 bat insulation. They installed 2x4 walls.
I would still like to get an R19 value out of that 2x4 wall. One insulation guy I just talked to was trying to pitch me a BIB L77 Insulation that has a "true" value of R15, that he said would be just as good or probably better than R19 bat insulation. I've also read that closed cell insulation would have a good R value. Not sure what options are out there or what would be best.

Any suggestions or thoughts would be greatly appreciated!
Thanks,

if the contrat specifies 2x6 studs, that what the framer needs to deliver. It is HIS problem. One solution would be to supply and install 2" x 1-1/2" furring.
Or, better yet, have him install 2" Styrofoam foamboard on the exterior, outside the sheathing. It will help your thermal performance much more than 2 more inches of fiberglass.

Posted By cladano on 19 Feb 2013 12:25 PM

I'm building a new home and the builder/framer/lumber company screwed things up. The plans for the house called for 2x6 exterior walls with R19 bat insulation. They installed 2x4 walls.
I would still like to get an R19 value out of that 2x4 wall. One insulation guy I just talked to was trying to pitch me a BIB L77 Insulation that has a "true" value of R15, that he said would be just as good or probably better than R19 bat insulation. I've also read that closed cell insulation would have a good R value. Not sure what options are out there or what would be best.

Any suggestions or thoughts would be greatly appreciated!
Thanks,

At a 20% framing fraction an R19 batt wall comes in at ~R13.5 for the "whole-wall" R, with all of the framing factored in.

At the same framing faction an R13 batt wall comes in at about R9.5.

If you pounded in L77 or Spider at R4/inch (R15) only raises the whole-wall performance to R9.75. 

How much are you willing to pay for R0.25?  Slipping in  1/4" XPS siding underlayment would give you R1 or so, but that still wouldn't hit the performance of the 2x6 wall.

Even if you put 3" of R7/inch closed cell foam in the 2x4 cavity it still comes in at ~R10.5.  (A full3.5" fill isn't practical with closed cell foam, since trimming it flush with the stud edges is nearly impossible.) That's about the same as the 1/4" XPS underlayment under a full-cavity-fill of mid-density fiberglass or cellulose.

If you add one inch of rigid EPS insulating sheathing to the exterior of the 2x4 wall with R13 (damp spray cellulose, open cell foam, or perfectly and I mean PERFECT R13-R15 fiberglass or rock wool batts) it will be equivalent to R19/R21 in a 2x6 wall.

If you add 2" of exterior foam and used 2 layers of foil-faced polyiso, seams staggered and taped with FSK tape (both layers), at the same wall thickness as a 2x6 wall you're now at ~R21-R22 whole-wall, which is a significant improvement over your original design.

In general sprayed or blown insulation has far fewer voids and compressions than batts. R19 batts are truly bottom-of-the barrel goods- they weigh the same per square foot as R13 batts- they're just "fluffed". Low density R22s aren't significantly better, but high density "cathedral ceiling" batts are the real deal (and the price shows it.)  With any compression or void the amount of air convection & infiltration through the material is HUGE compared to higher density goods.  Rock wool batts are comparable in density and performance (and price) to the high-density fiberglass batts, and are in some ways preferable (fire resistance, and fewer issues with binders outgassing, no issue with suspended micro-particles floating in the air, etc.)  But damp sprayed cellulose is often cheaper than high-density batts (and definitely cheaper than L77 BIB), and far greener in most respects.

So, if I were in your position, I'd hold out for an inch or more of foam and damp-sprayed cellulose.   Rather than long-nailing through the foam causing 10,000 thermal bridges to ruin the performance, use 1x4 furring through-screwed to the studs 24" o.c. to give you something to hang the siding on, leaving a "rainscreen" air gap, which allows both the sheathing and the siding to dry better/quickly.  It's always better to use 2 layers of foam and stagger the seams, but you can also be OK with 1-2" XPS  (pink, blue, green, whatever) with ship-lap edges (not the t & g), which keeps heat leaks from opening up as the foam shrinks slightly over the next couple of decades. Tape the seams with housewrap tape, and foam-seal the edges with can-foam or FrothPak.

Caulking the studs to the sheathing in each stud bay and every seam at the stud plates/subfloor/band-joist/foundation sill interface with acoustic sealant caulk can make the wall assembly more air-tight than merely insulating the stud bays with spray foam, and is about the cheapest performance upgrade to the thermal performance of a wall you can buy. (Foam seal every electrical penetration of the studs too.)

With enough foam-R on the exterior you can skip interior vapor retarders, which makes the assembly more resilient to wetting events.  The minimum amount of foam necessary varies by climate.  If you don't know your climate zone, find yourself on this map.  For reference, an inch of EPS is ~R4, an inch of XPS is ~R5, and an inch of iso is ~R6.

Yup- it's a blessing in disguise, if the contractors can wrap their heads around how to do insulating sheathing right. (I would always take R13+ R5 foam 2x4 over R20 2x6 where code minimums spell out either. The R13 + R5 is a more resilant assembly, far less susceptible to mold and other moisture issues.)

EPS and iso typically costs about 9-10 cents per R per square foot, maybe 12 cents installed. XPS (Styrofoam tm) costs maybe 12-13 cents per R per square foot or 15 cents/ft installed. L77 BIB at 1.8lbs density can be even more expensive than that, depending on the contractor and local labor rates, and that expensive R15 cavity-fill buys you less than R1 in whole-wall performance. For 1" EPS on the exterior, figure 50 cents per square foot, installed price. For 2" iso, call it a buck-twentyfive a foot.

Save the expense for the insulating sheathing, keep the cavity fill cheap (as long as it's a full-fill/no-voids or compressions, which is hard to do with batts, but dead-easy with damp-spray cellulose, open cell foam, or BIB goods.)

How feasible is it to put styrofoam on the outside if they have the wood sheathing, tyvek, and windows already installed?
Thanks!

sounds like you are at the (almost) perfect stage to do that! Be sure the Tyvek seams are completely TAPED, Install the styro and tape it to the window, add a window casing, strapping for the siding, installl the siding and you're all done!

Can you use the closed-cell spray foam directly on the concrete foundation walls in the basement?

Yes! Its an excellent appllication for CCSF. Insulates the basement while preventing moisture from coming into the house through the concrete. It does need to be covered by a fire retardant material. I use 2" ccsf, then add a stud wall (set 2" off the concrete) filled with R19 fiberglass, covered with Tyvek. (the ccsf is overlapped onto the studs to air seal the back of the stud wall.)

Yes! Its an excellent appllication for CCSF. Insulates the basement while preventing moisture from coming into the house through the concrete. It does need to be covered by a fire retardant material. I use 2" ccsf, then add a stud wall (set 2" off the concrete) filled with R19 fiberglass, covered with Tyvek. (the ccsf is overlapped onto the studs to air seal the back of the stud wall.)

Due to the high greenhouse potential of the HFC blowing agents for closed cell spray polyurethane I tend to prefer rigid EPS or polyiso (and NOT XPS, which uses even more damaging blowing agents than ccSPF) for insulating foundations. While there are newer lower-impact blowing agents coming on the market (Honewell just released it last November), most of it is blown with HFC245fa, which has ~1400x CO2 greenhouse potential. This compares to 7x greenhouse gas potential for the pentane used to blow EPS & polyiso.

There are two ccSPF products that I'm aware of currently out there that are blown with water rather than HFCs:

Icynene MD-R-200, which runs R5.2/inch (not to be confused with MD-C-200, which is blown with HFC2245fa)

Aloha Energy is a regional player in the northeast with a line of water-blown foam at a few standard densities (including an R6/inch 1.8lb foam.)

Depending on your local climate and fuel sources and the application, anythiing past the first inch or so of HFC blown foam will have a greater greenhouse gas footprint than the energy use it's offsetting, for below-grade apps. Bump that to maybe 2" for above-grade. It's complicated math on fuzzy models, and the particulars will vary, but it's hard to make the case for more than 2" in ANY application or location on greenhouse gas issues. If possible, design around it.

At 17-20cents per R per square foot it's about the most expensive insulation you can buy anyway, but from a design point of view the ability to adjust vapor retardency is useful.

If you're using the foam on basement walls against the concrete, the sheet goods will work fine as long as it is air sealed top, bottom and sides so that air cannot get behind the sheets. GreenBuildingAdvisor.com has an article by Marc Rosenbaum about that subject where he has several photos showing the basement insulation project he did at his house in 2012.

Or, you can just refer to Marc's original writeup found on his own "Thriving On Low Carbon" blog:

http://blog.energysmiths.com/20...gress.html

http://blog.energysmiths.com/2011/0...art-2.html

http://blog.energysmiths.com/2011/0...art-3.html

He used fire-rated iso to get around the ignition barrier requirement, since he was not intending to fully finish the basement.  If you intend to make it a fully finished space the gypsum wallboard will meet spec for the code required ignition barrier for ccSPF or non-fire-rated rigid foam.  

Trapping the rigid foam behind a studwall and using unfaced batts between the studs works fine, but so does strapping through-screwed to the foundation 24" o.c. with TapCons, hanging the gypsum on the strapping

I recommend you stay away from cc foam on the foundation walls and stick with prefabricated panels. The surface temperature of the wall will never meet the manufacturers application surface temperature. I had this process done in my home and the foam never cured at the contact point even though the surface was cured. Dangerous stuff!

Here's an example of one homeowners fight with industry and what happened in his home... Looks like industry will be answering to government now.

http://landing.newsinc.com/shared/video.html?freewheel=91060&sitesection=WTIC_hom_non_fro&VID=24462819

I watched some of the video- it indicated problems not with spray foam, but with untrained and uncaring installers. The lesson here is not to avoid it, but to hire a good experienced installer with a track record - not the cheapest price you can get. I use spray foam on foundations all the time - it works great!