I'm designing a high thermal mass house built from 12" CMUs with built-in insulation on the outer half... pretty neat things. The intent is to have a well-insulated shell to protect the internal thermal mass. I'm having trouble thinking about the garage though. Having it attached seems like it could just cause problems. If it's thermally separated from the rest of the house, then you have to worry about thermal bridging through the slab and the attic; if it's in the same conditioned thermal zone, you have a mostly uninhabited space sucking up energy and losing a bunch of heat every time the garage door is opened. But detaching the garage has all of the problems of its own: a whole separate structure, more space and money required, etc. What do you think?

Make it attached but with thermal breaks.

Where are you building the house? Do you have a link to the cmu's?

Posted By jonr on 22 Nov 2013 02:30 PM
Make it attached but with thermal breaks.

Could you elaborate a bit? Like, two separate slabs (one for the garage, one for the rest of the structure) separated by insulation or something? Insulating the shared wall won't be hard, of course. How about the shared roof? Just insulate the part of the attic above the non-garage part of the house and not care about the air from the garage entering the attic?

Posted By FBBP on 22 Nov 2013 02:48 PM
Where are you building the house? Do you have a link to the cmu's?

Albuquerque, NM.
http://www.energyefficientblock.com/

How are the inside outside protected from each other if the grout line is left open over the foam?

If the mason lays mud on the insulation it will also thermal connect.

Posted By FBBP on 22 Nov 2013 03:51 PM
How are the inside outside protected from each other if the grout line is left open over the foam?

If the mason lays mud on the insulation it will also thermal connect.

I think the intention is that the grout would touch the block part but not the built-in insulation. Leaving air between the insulation hopefully wouldn't be a disaster because air itself is a decent insulator when it's not able to move around too much. I'm also investigating dry stack, which seems like it would be of use in addressing those concerns with this block.

Their R-Value claims are worth reading carefully!!!

Posted By FBBP on 22 Nov 2013 04:15 PM
Their R-Value claims are worth reading carefully!!!

Indeed. I exchanged emails with their engineering department because I was skeptical too. There are documents on their site with the result of testing, showing a steady-state R-value of 10-11 depending on the temperature. With 8" of sheltered mass on the inside (with concreted cores), that's not too bad IMHO. IBC code for insulation on the outside of a mass wall requires only R-5 for zone 4 but R-13 for zone 5. The manufacturer says that they have structures made with these blocks in zones 5 and 6 too and got approval in those places by stating the "effective" R-value of 22, which includes the mass. The case studies available on their site of actual energy used in structures made of these blocks were impressive to me.

How does this compare to ICF in terms of cost and thermal performance? I didn't see a comparison on the website.

Using a dynamic-mass loaded "effective R-value" is very squishy number and quite problematic, and you can't mix and match: The steady-state R-value of the EPS in the block need to be the IBC/IRC R-value for mass walls (which already take into account the mass benefit). To use the "effective R-value"  that already has a mass-effect built into it and then apply that to the IBC would be double-dipping.

The IRC 2012 calls out R8 for zone 4, R13 for zone 5 for mass walls, and only if at least half the insulation is to the exterior of the mass. And that's a steady-state number- the dynamic mass "effective- R" from an energy use and peak heating/cooling load will be higher, but how much higher depends a lot on the local climate particulars.

The dynamic benefit primarily accrues to peak-loads, the net energy-use benefit of that mass varies, but is rarely into double-digit fractional reductions when compared directly to identical lower mass construction of the same steady-state "whole wall" R.  The marketeers will of course claim that the performance their cherry-picked case study buildings is achievable (which it sometimes is, at least in the example), but the amount of other design aspects that went into those buildings to tease that performance out isn't usually detailed.  What's lacking is the side-by-side comparative of otherwise identical buildings with details of the alternates' construction by which the average U-factor and thermal mass of the walls can be calculated.

The Oak Ridge National Labs has in fact built identical code-min R13 stick framed houses next to R15 insulated concrete form walled homes, and run batteries of tests on them.  No big surprise- the ICF house outperformed the stick built house by low double digits, but the "whole-wall" R of an R13 stick-built is about R10 with the thermal bridging factored in, making even the steady-state R of the wall area of the ICF 50% better than the stick built even before modeling the mass benefit.  The results of both measured within the construction error tolerances of the modeling of each using DOE2 (now a freebie download energy modeling tool.)

The amount of EPS in the NRG Block looks to be significantly less than that of an R15 bottom-of-the barrel ICF (but more optimally placed), with significantly more surface area of the foam/concrete interface.  It also doesn't appear to thermally break the mortar seams, nor is it as inherently air-tight as ICF.

Bottom line, until you've seen the true details and analyzed it fully, try to restrain the welling sense of awe. :-)  There is a lot of hype in the industry, and only a small fraction of it bears out when you change up the application beyond the very narrow scope of the examples.

ICFHybrid
Read the report under R value. You will enjoy it.
How do you think the narrow about 1" of eps will compare to the 5 plus inches of foam and 6 inch of solid concrete to open cmu?

I like detached garages - better for your home's air quality and safety, no shared wall, no worries. Later you can put a window unit in and make it a mother-in-law suite. You might consider a drain for the sewer and don't forget to run some conduit underground for electric.

Posted By ILikeDirt on 22 Nov 2013 04:27 PM

Posted By FBBP on 22 Nov 2013 04:15 PM
Their R-Value claims are worth reading carefully!!!

Indeed. I exchanged emails with their engineering department because I was skeptical too. There are documents on their site with the result of testing, showing a steady-state R-value of 10-11 depending on the temperature. With 8" of sheltered mass on the inside (with concreted cores), that's not too bad IMHO. IBC code for insulation on the outside of a mass wall requires only R-5 for zone 4 but R-13 for zone 5. The manufacturer says that they have structures made with these blocks in zones 5 and 6 too and got approval in those places by stating the "effective" R-value of 22, which includes the mass. The case studies available on their site of actual energy used in structures made of these blocks were impressive to me.

If you are going with thermal mass design. Stick with what is tried and true and just do with the standard ICF block that has 2.5" of EPS foam x 6" of concrete x 2.5" of EPS foam. It's stronger, monolithic and gives you a Steady State R-Value of R-21. The ORNL Thermal Mass Calculator Dynamic R-Value Equivalent is around R-32 (depending on climate). If you are in New Mexico, then it would be closer to R-40 for the Effective DBMS. You have zero thermal bridging with standard ICF's. Air Leakage (infiltration rate) of 0.05 to 0.10 ACH (average air changes / hour). A 2 - 4 hour fire rating (8" concrete core would be closer to 4 hours) and STC Ratings of > STC 53

I would stay away from that block you found and stick with the commonly used ICF that is out there.

The above mentioned R-Values are openly stated by ICF manufacturers like Nudura and Fox Block. The statements are reviewed by the FTC and if they were inaccurate, they would be removed and fined by the FTC. As Dana mentioned, I would focus on the Steady State R-Value which is R-21 for blocks like Nudura. The Effective number can lead to problems and of course, debate.

Wow, thanks for all the replies, guys. The reason why I'm not so hot on IFCs is that most of the ones I've seen don't use the benefit of the insulated concrete thermal mass to store and release heat and cold because it's insulated from the interior side too (d'oh). If only one side was insulated, I'd be all over ICFs. It's similar to the problem with taking standard CMUs and filling the cores with insulation. The Fox blocks and Ndura products seem to have this problem because they insulate the concrete thermal mass from both sides.

I'm not dogmatic about the product. I just want a wall that has insulation near the exterior, mass on the interior, and won't cost an arm and a leg in money and time like it would patching together a layered system consisting of drywall + furring + mortared CMU + flashing + furring + foam insulation + siding. What attracted me to the NRG blocks was the simplicity; dry-stack the blocks, apply SBC to both sides, pour concrete in the cores, and the whole wall is finished.

Posted By ILikeDirt on 22 Nov 2013 06:48 PM
Wow, thanks for all the replies, guys. The reason why I'm not so hot on IFCs is that most of the ones I've seen don't use the benefit of the insulated concrete thermal mass to store and release heat and cold because it's insulated from the interior side too (d'oh). If only one side was insulated, I'd be all over ICFs. It's similar to the problem with taking standard CMUs and filling the cores with insulation. The Fox blocks and Ndura products seem to have this problem because they insulate the concrete thermal mass from both sides.

I'm not dogmatic about the product. I just want a wall that has insulation near the exterior, mass on the interior, and won't cost an arm and a leg in money and time like it would patching together a layered system consisting of drywall + furring + mortared CMU

Internal thermal mass is not inexpensive, no matter what route you go, it's always going to cost more $$$ than wood frame.

You are partially correct in the thermal mass location. Yes, ideally having the entire thermal mass exposed to the interior works best BUT having it in the middle doesn't negate the thermal mass benefit. Does it reduce it? Somewhat. But it doesn't eliminate it. ICF offers a thermal mass benefit, even though it's covered by 2.5" of EPS on the interior.

If you want 100% exposed thermal mass on the interior wall, you are going to be limited in your choices and pricing $$ will rise. You can use SCIPs but that is very regional limited (not available everywhere) and NOT a DIY and more expensive $$ than ICF.

I would not go the route of CMU's.

As far as attached or detached garage. I believe detached is better and easier to deal with on an energy standpoint but if you don't have the lot space, you will default to attached.

Attached garages require a lot of attention to details to make sure the shared wall is well insulated and air sealed. You don't want vapors/gases from your vehicle entering your home space.

I went with a detached garage on my home but lot space is plentiful.

Thanks for your thoughts, Lbear. So you would go with ICFs, then? Would you avoid CMUs for the reasons I gave (gets expensive and complicated with all the different layers)?

All I'm really trying to do is design a not-too-expensive house that takes advantage of northern New Mexico's climate, which includes abundant sun and large daily temperature fluctuations. I'm willing to spend some more bucks to avoid stick framing, but I guess was hoping to hold down the costs a bit which maybe isn't possible.

Posted By ILikeDirt on 22 Nov 2013 10:50 PM
Thanks for your thoughts, Lbear. So you would go with ICFs, then? Would you avoid CMUs for the reasons I gave (gets expensive and complicated with all the different layers)?

All I'm really trying to do is design a not-too-expensive house that takes advantage of northern New Mexico's climate, which includes abundant sun and large daily temperature fluctuations. I'm willing to spend some more bucks to avoid stick framing, but I guess was hoping to hold down the costs a bit which maybe isn't possible.

Yes, I am building with ICF. As far as CMU's go, the reasons you gave are valid reasons for not going with CMU's but I would also add that CMU's are not as strong as a monolithic concrete wall and do not have the same mass as a monolithic 6" concrete wall. In addition, CMU's are not as airtight as an ICF wall.

As a ballpark cost for ICF, calculate your wall square footage (including windows and doors) and then once you have a wall square footage, use a multiplier of $12 per square foot (including window and door space). For example, if you have 2,000 square feet of wall space, your ICF costs would come out to around $24,000

This $12 per wall square footage would include everything:

• ICF block costs
• re-bar
• concrete
• labor
• window and door bucks

And then toss out Lbear's estimate and call a local ICF contractor to get real numbers. Some markets are competitive (many ICF contractors who know what they are doing.) Most are not. Unless your house is huge, walls are not a big deal in energy use. I built an R-8ish high mass house in Pa., which is a far less favorable climate for mass effect than Alburqueque. My all-in energy bills heating and cooling with a 2-ton minisplit are roughly $50/month. My current bill is $27.73. If it was twice its size of 1600 SF, ICF at premium prices might pay for itself. (One ICF guy around here is really good.) MIGHT. In a small house, spend your money on air sealing, attic insulation and windows.

A caution about dry stack. Because variances grow as the wall gets higher, make sure your first course is as perfect as you can get it. Also ask the manufacturer what tolerances it guarantees. My block (AAC) was milled on the mating surfaces for a tolerance of a sixteenth inch. But fouir courses up, you can have a quarter-inch problem. There is a reason cmu is set in three eighths mortar. Dunno the protocol for your block, but thin set mortar would give you an eighth inch to play with and .

If only one side was insulated, I'd be all over ICFs.

If ICF block had only one side, things would get messy during the pour. Alternatively, you can spend a few weeks with a claw hammer, ripping all the insulation off the inside. However, having the concrete sandwiched between two layers of EPS isn't a total fail. You need to look at how the thermal characteristics of your "mass wall" and traditional ICF really compare.