I'm building my personal home in Charlotte, NC with the following specifications: 2200 sq.ft. ranch with full basement below, full brick veneer, tyvek house wrap, large attic area, geothermal hvac, low e windows, rear of the house facing due south, decent shade at times, and am currently contemplating insulation. I can't decide what method of insulation to use for the attic. For the walls I'm thinking about going with wet blown cellulose. In the attic, one installer wants to go with closed cell foam, while another recommends blown cellulose over the attic floor. Any recommendations as to the best value/air sealing/insulation for the money would be greatly appreciated specific to my zone. Also, code for the attic is R-32 I think. If I do 3" of closed cell in the attic that's approximately R-20. Where does the remaining R-12 come from. One installer says I don't need it. Any thoughts? Thanks in advance for your time.

Are you aware of stabilized cellulose attic insulation?  I wasn't until just recently.  You can google it for more info. 

I posted a thread on here a while back, but didn't get much response.

Stabilized cellulose attic insulation

arkie6,
I haven't heard of that, but I appreciate you saying something about it. It sounds interesting and is something that is going on my list of things to ask potential insulation contractors. Have you already gotten past the insulation stage in your home? If so, what did you end up going with. My HVAC is also in the ceiling of my basement, so I wouldn't receive any benefit towards that from attic insulation regardless of what I go with. However, I would like something that is going to give me the most energy efficiency effectiveness bang for the buck. stabilized cellulose attic insulation might do the trick. My ceiling joists are 12" OC so it might not be a problem anyways.....

Stabilized cellulose is another term for wet-spray cellulose. The "stabilized" refers to the water activated adhesives that prevent settling/sagging over time.

An inch of closed cell is sufficient to form a perfect air-barrier (and class-II vapor retarder), over which you can blow the cheaper goods.

The "...you don't need more than..." argument often made by foam installers is complete BS.

What they're really saying is "... if you're using only this premium-priced premium product its not cost-effective to go deeper...". The "extra" R12 really IS missing (it doesn't meet code).

At typical 1.6-1.8lbs per cubic foot densities of open blown cellulose (wet sprayed or dry) the convection & infiltration losses are quite small- it performs well at any temperature (unlike standard density fiberglass batts, which become lossy and don't perform to spec at high delta-T in winter). Using spray foam for only air-sealing the attic floor and dry cellulose for the rest is usually a very good value. With an air-tight attic floor you can go much higher R for the same money as going only R20 with closed cell foam. Be sure to design the framing or rafters such that you get the full-R all the way out to the exterior of the exterior walls though, with sufficient room for attic ventilation. (If it's a trussed roof, look for an "energy heel" to give it the full insulation depth at the ends.) And be sure to make the attic access as air-tight as possible to reduce heat losses or potential attic condensation/frost issues in winter, no matter what you use for insulation.

In windy areas dry-blown goods can move around on you near the soffits due to air currents through the attic ventilation, whereas stabilized goods stay put. Dry blown is usually installed at greater depth, to ensure it's settled-R meets the spec decades later. Either can be added to a later date, if desired, but watch out for the total weight, which can be substantial at R60+. Be sure the ceiling materials supporting it are rated for the load before going more than 15". At 12" o.c. joist you're probabably good for quite a bit though.

But at 12" o.c. you also have a lot of thermal bridging- the center cavity may be R38-R40, but the joists are only ~ R10, and are 13% of the total exposed surface area. Burying the joists by at least 3" would double that to R20 at the joists, making a substantial increase in performance well beyond the extra ~R11 you'd get center-cavity.

Note, all wet-sprayed or "stabilized" cellulose uses only borates for fire retardent, but some dry-blown product still contains sulfates (usually aluminum sulfate) which become corrosive to metals when wet. Be sure to specify "borate only" or "sulfate free" for quotes on dry-blown.

Thank you for the response dana1. When I posted on this forum, I was hoping you would respond. I've read many of your posts and appreciate you backing your information up with links to reputable sources (oak ridge and building science amongst others).

Thanks for the clarification on the stabilized cellulose. I am with you on the "you don't need more than that" argument. The installer that I was talking with said that I could get around code by something called a rescheck from the department of energy that superseded the local code for insulation in the attic. That sounded good, but at the same time I was thinking "with that work around, that still doesn't mean that I have R-30 insulation in the attic". I know that the r value is a reciprocal of a heat transfer coefficient and if the airflow is taken out of the equation, the higher the r value, the less heat flow I would get so I didn't full trust him in saying that I didn't need what code called for (especially a difference of R-18 vs. R-30).

With regards to the spray foam for the first inch and blown cellulose after that, I like that idea. I had thought about spraying under the roof, but with my HVAC in the basement, I just don't see the need. There's no plans for making a room above either as the attic area is pretty cut up. The only possible room addition in the future is over the garage so it's unlikely that I will do anything like that (especially with the basement area I have). And even at that, the garage trusses only give storage, not room enough for another whole room.

Thanks for the heads up on designing the framing and rafters to take into account the full R all the way out to the exterior. One would think that's always taken into consideration, but I know it's something that I didn't think about until you said something.

I do have a few clarification questions if you don't mind. I know you said you get good bang for the buck doing 1" of spray followed by wet or dry blown cellulose. And that the spray would give a perfect air-barrier (and class-II vapor retarder). What would happen if I went with just wet blown cellulose and didn't do any foam? In other words, with convection and infiltration losses small with wet blown cellulose, what would the spray give me that I couldn't get otherwise? And how important is a vapor retarder in the interface between the attic and main level?

Thanks again for your time in advance....

If you go with just wet-sprayed low-density cellulose you'd be fine in your climate zone, as long as you don't have significant air-leakage paths from conditioned space. Spot-sealing around all plumbing & electrical penetraings, boxing over recessed lighthing, providing fireproof air barrier (and insulation clearances) around any flues, etc. are best detailed out prior to insulating.

Vapor diffusion through a latex-painted ceiling is fine, but steady air leaks are both an energy leak, and can potentially create condensation conditions when it's much below ~37F in the attic, assuming 68F, 30% relative humidity interior space air. Air-sealing is always job-1.

Pressure-door testing to find leakage points before insulating is best. This is true for your wet-spray cellulose walls as well. If you install all the doors & windows first, then pressurize/depressurize and run around finding & fixing all the leaks with spot-foaming/tape/caulk it's possible to make the place pretty tight without resorting to a full-assembly SPF treatment.

If you can slip even 3/8" of fan-fold XPS between the Tyvek and the sheathing you'll give it sufficient vapor retardency to limit the very high vapor drives that can occur in the cavity when the sun hits rain/dew wetted brick veneer. Try to leave a least an inch of cavity space between the brick & Tyvek as well, with the requisite bottom-course weeps and top course vents (or open top cavity vented to the exterior, if well protected from rain incursion) to allow the cavity to purge the humidity to the exerior. Treating the brick with vapor permeable silane-based masonry sealers, and using metal or 10mil poly as a capillary break between the brick & foundation (copper flashing is best in termite prone regions) will reduce the uptake of bulk water from capillary draw into the masonry, reducing peak vapor drives toward the interior. With brick or stucco facing Tyvek alone may not be sufficient to keep the humidity in the sheathing low enough.

Up to an inch or so of XPS would still allow water vapor to escape the studwall in winter at roughly the same rate that it diffuses in through latex in the interior, but also puts the brakes on those summertime peak drives that occur with masonry veneer. XPS goods can be turned into a decent air-barrier as well by taping seams & foaming edges. 1" XPS becomes a significant thermal break on the studs, roughly doubling the R value at a 2x6" stud edge- where it was ~ R5 at the studs it's now R10, even if it's only boosting the center-cavity R from ~R20 to ~R25. (R5 thermal shorts through an R20 cavity fill become a large fraction of the total heat loss through the assembly.) But even 3/8" goods make a sufficient vapor retarder.

Dana1,
Thanks again for the information. I think you've given great advice with regards to insulation and I'm right there with you in thinking that air sealing is job 1. I'll take these recommendations into consideration and try and incorporate as many as possible into my building envelope. I don't see why I can't do all of the above.

I also like the idea of the XPS on the exterior between the brick. The only problem that I'm facing is that my poured walls are done and I don't have the offset for the brick ledge to put xps between the brick and tyvek. I can do the following:
1" cavity between brick and tyvek
bottom course weeps
open top cavity
capillary break between the brick and foundation

Since I can't do XPS on the exterior, would this necessitate closed cell spray on the interior walls to reduce the vapor drive. I know it won't be as effective as the exterior XPS, but it's about all I can do now. Or will I be fine with good air sealing and cellulose with it's hygric buffering?

Lastly, what are your recommendations for the poured walls in the basement. I imagine XPS on the exterior before backfill, but I still have a significant amount of my poured walls above grade faced with brick due to the lay of the land. What's the typical treatment on poured walls on the interior living space? I would think a vapor barrier would be a bad idea but want to get your thoughts on this area....

Thanks again for all your help. This forum is great, very informative and extremely helpful.

Okay, just to throw it out there, if you are doing a ranch with a full basement, why not opt to go ICF up to the roof, then spray foam to seal up the attic followed by wet-sprayed low-density cellulose for insulation in the attic? The would be the optimum for energy efficiency. Yes, I realize that the ICF would be slightly more expensive than the frame construction above grade, however it is a ranch so you have to have some sort of foundation anyway...so below grade the cost difference would not be huge. Plus if ICF it would be quieter, wouldn't settle, less maintenance over time, etc.

I would then consider opting out of the geothermal and go with a high efficiency SEER HVAC. A house of the size, but like that would be very close in cost and efficiency if not moreso than what you are considering. Depending on the cost of the HVAC (tax credit) Geothermal may be close in cost, but if the geothermal is much more expensive the rate of return would be pretty long in my opinion of couse.

Just a little thinking outside of the box possibility.

renangle,
Thanks for the recommendation - I had thought about going that very route and think that it's the best way to build. However, I have family that works in poured walls construction and the cost difference based on that fact was too great to pass up. Without that difference in cost, I would have went with ICF, however, I've already done the poured walls. Good thinking though....

With all due respect to your family in the poured wall business...why not look at doing it in ICF as an easy way to enter into the ICF business. It would enable them to extend the line of services to clients for very little cost.

What would happen if Apple didn't want to expand past the Mac?

That first-ton of geo is pretty expensive (it buys a heluva lot of cellulose & air-sealing), but that wasn't the question now, was it?

Going truly high-R with ICFs can be expensive too, since it's a mostly-EPS show. People going all PassiveHouse or Net Zero tend to do it with thick thermally-broken air-tight frame construction and blown cellulose or blown fiberglass + several inches of EPS.

R35 walls/R60 roof & U0.3 windows heated & cooled w/air-source heat pumps may cost less overall and use less power than an R20/R38/U-0.5 glazed house heated & cooled with geo. It's likely that R45walls/R70 roof with carefully calculated quality, sizing & placement of glazing could meet PassiveHouse standards in Charlotte NC, (at which point it doesn't need a heating system) but that's a different project, different spec.

enangle,
Good idea on breaking into the ICF construction aspect. The problem is that I have family that works in the poured wall business, but they don't own the business. They are a large operation that has significant money invested in the forms and most of their work is commercial. The choice to do poured walls was mine based on the cost comparison between the two. I also had some issues with ICF construction in regards to the maximum height of brick veneer that the ICF construction would support. One eve on the end of the house is pretty high and he load associated from the veneer would have been too great for the brickledge.

Dana1,
The first ton of geo is pretty expensive - without the tax incentives it wouldn't have been an option. I did price out the ICF and I think it's a good idea, but also pretty expensive from what I can tell as well. I think some of the technologies are good, but I'm not convinced that depending on the climate that one lives in that you can't do just as well cheaper and being exceptionally smart about it.

I started out with a south facing rear of the house, and graded the land to take advantage of the sun with tree placement and whatnot. I wanted to be reasonable on the expense side of things incorporating features that would provide good payback without breaking the bank and have quickly found that one can in my opinion go overboard with going green.....forums like this help and I appreciate all the information and help that has been presented.

I could have done things drastically different, but I'm hoping that the combination of insulation, geothermal, radiant floor heat, good windows and passive solar will give me a decent rating on the home while leaving some funds to live off of. I sometimes wish that I would have went overboard and tried for a total passive house, but nothing perfect right?

Do you have an opinion on the following:

Since I can't do XPS on the exterior, would this necessitate closed cell spray on the interior walls to reduce the vapor drive. I know it won't be as effective as the exterior XPS, but it's about all I can do now. Or will I be fine with good air sealing and cellulose with it's hygric buffering?

What are your recommendations for the poured walls in the basement. I imagine XPS on the exterior before backfill, but I still have a significant amount of my poured walls above grade faced with brick due to the lay of the land. What's the typical treatment on poured walls on the interior living space? I would think a vapor barrier would be a bad idea but want to get your thoughts on this area....

Painting the exterior of the sheathing (the side facing the masonry) with a quality latex or acrylic latex primer and taping the seams ( or using Huber Zip sheathing) would be enough. Closed cell on the interior would only trap the sheathing in the humid cavity-space, limiting it's ability to dry toward the interior. Standard latex primer is a Class-III vapor retarder, about as vapor-retardent as dry 15lb felt, (MORE vapor retardent than damp or humid 15lb felt), and felt has a long mostly-successful history with plank sheathing & brick veneer. Plywood is a better air-barrier than planking & felt, and it's vapor retardency goes up & down with moisture content, which works in it's favor. When exterior vapor drives are high enough to add moisutre content to the ply through the latex, it's better able to pass it on through to the cellulose. (Plywood is much better than OSB in this regard, but OSB does too, but at a lesser degree at the extremes of moisture content.)

If insulation the foundation exterior borate-loaded "termite resistant" EPS would likely be cheaper and better-performer than XPS long term. Waterproofing it below grade before backfill is also recommended (there are likely multiple threads on the insulated concrete forms forum on how to do it, which product are easier/better, etc.). The EPS can extend up behind the brick as well, using standard cavity-wall methods. Insulating on the exterior places the thermal mass of the foundation on the inside of the thermal envelope, which will have a measureable improvement on overall heating/cooling efficiency. If you can, that's the preferred way to go.

If it need to be insulated on the interior instead, first used a vapor-permeable silane/siloxane masonry sealer to limit capillary draw & efflorescence issues. But it must be vapor-permeable- the foundation needs to be able to dry toward the exerior, or else it'll raise the humidity at the sill (for potential rot), and cause efflorescence on the above grade portion as it dries toward the exterior (and spalling, if it's damp enough during freeze/thaw cycles.) Use the same sealers on the exterior of the brick or any exposed above grade concrete to slow the uptake of rain or dew as well.

Then, use permeable or semi-permeable rigid board foam glued to the concrete with foam-board construction adhesive works. Foam-seal the top of the foundation to the foam board with 1-2" of closed cell spray foam, as well as the band joist. Over the foam-board one can apply furring through-screwed into the foundation on which to mount the code-required half-hour fire barrier (half-inch sheet rock is good enough.) On my home retrofit I did 4 lateral runs of furring, but vertical furring 16" or 24" o.c. works too. There are also system-products (eg InSoFast) that you might price out as well.

UN-faced EPS (up to 5" before it's too vapor retardent) is typically the best value in terms of R/$, and allows you to go up to R20 as an all-foam insulation eating up minimal floor area. With XPS you're limited to ~2", but you could then build a studwall and use lowly un-faced batts to raise the total R. Some fiber-faced iso sold as roofing insulation in commercial construction is sufficiently vapor permeable to work as well. But under no circumstances should poly or foil-faced goods be used (far too vapor retardent.) As long as the foam is against the foundation, and it accounts for at least 1/4 of the total R (in your location), using a fiber/studwall on the interior is fine- the studs should stay dry enough to avoild mold.

The interior finish also needs to be vapor permeable- oil paints, vinyl or foil wall papers etc are too vapor retardent. Latex or acrylic-latex paints are fine.

Price/performance-wise I'm not enamored with the ICF approach for the whole house, particularly if the goals are R35+ clear walls but it's a labor saver for insulating foundations, and tends to be pretty air-tight if you're diligent on how you do the roof/attic.

And yeah, nothing's perfect, and various incentives WILL drive the price/performance issues differently- I'm not into criticizing every design decision. But un-subsdized the rationale for going high-efficiency geo vs. high-R building envelope is hard to make for sub-4000 s.f. houses in new construction. It's easier to make the geo rationale as a retrofit for modestly insulated older homes. It takes a very sharp pencil to parse out the whole thing sometimes. In Charlotte the heating season performance of geo will be significantly higher than in coldwater areas like New England or the upper midwest, for sure! (Your deep-well temps are 12-15F warmer than near me, for instance.) If you have the time & inclination, the PassiveHouse tools are pretty good for tweaking in the passive-solar aspects of your place, and will model your heating & cooling loads far better than ACCA Manual-J methods used by HVAC contractors.

dwhood,
I read that your poured concrete foundation is done... have you started framing the house yet? If not, you could move the framing of the house inwards to allow for foam board on the exterior without losing space with the brick ledge. If you want to use 1" foam board, your floor joists and rim board would be pulled in that same thickness of 1", this would allow the foam board to extend down to the foundation covering all of the framing... also the exterior side of the foam board would be flush with foundation and you would still have the same amount of brick ledge to work with. Doing this, you will lose 1" (or whatever thickness of foam board) from the rooms around the exterior walls.