I am considering a block house using http://crescoconcrete.com/ Liteblok 38 which claims to have an R value of 35. I am wanting to have this house built in the high desert of New Mexico and none of the walls will be covered with earth. Temps can drop to 0 each winter and I was wondering what options would be best to up the R-value of the walls. My first thoughts would be to add a timber wall on the inside for both added insulation and electrical/plumbing. Thought on this please as I don't want to make a mistake adding the insulation on the wrong side of the wall ruining the R-value.

It doesn't claim to have an R value of 35. It claims to have an "equivalent" R value of 35. The claimed block properties are 0.759 BTU-in/hr-ft2-°F. That is R1.3/inch thickness. The Liteblock 38 standard block is only 4.92 inches thick which results in an actual R value of ~6.5. The Grande block is 7.87" thick which results in a actual R value of ~10.4. Not anywhere close to R35. Even taking into consideration the mass effect in an optimum climate you might get an effective R value at most of 1.5x the actual R value or R10 for the standard block or R15 for the grande block considering the block density is only 38 pounds / cu ft compared to standard high density concrete at ~150 pounds / cu ft.

Thanks for the break down of the blocks pun intended. That is why I come here and ask these questions. Now what is the best way to increase the R value of the block wall in my area? I would still prefer to fur up the inside and add some spray in foam.

Placing the mass on the inside of any added insulation will enhance the interior temperature stability, which is usually a desireable property for any dwelling. I can also understand your desire to add an interior frame wall for conventional construction, but the insulation should probably go on the outside.

I would say insulate the outside with a few inches of foam. 2" of foam outside the thicker block might get you near R25? Then build your interior stud wall without insulation. An issue you can run into with interior insulation over the mass is if the inner face of the mass/block goes below the dew point, you can condense and buildup moisture inside your wall which is generally considered to be a very bad place to collect moisture

When it is 0 degrees outside, the mass will add no "effective" R value. Consider building with something else.

Posted By jonr on 13 Feb 2016 04:50 PM
When it is 0 degrees outside, the mass will add no "effective" R value. Consider building with something else.

Makes me wonder why they built so many adobe homes in that area for 100's of years with no problems. I was hoping to mimic the adobe affect but using modern blocks.

Liteblok is not a true AAC (autoclaved aerated concrete) is it? So the relative R-value is not as good. I think you could do just as well using regular CMU (concrete masonry units, also known as concrete blocks) and adding insulation on the exterior. The advantage of Liteblok is that they interlock, but you can also stack CMU without mortar and use a surface bonding cement, or grout the cores with concrete.

So I think it would be best to install The Grande block with spray expanding foam on the outside finished with stucco to give me the adobe look, but much stronger than adobe and better insulated.

How will you get a flat exterior wall with spray foam?

Posted By arkie6 on 15 Feb 2016 12:32 AM
How will you get a flat exterior wall with spray foam?

Add 3" fur strips and affix plywood to the fur strips creating a 3" void. Drill holes and have foam spayed in so it will expand to the exact size of the space. Prep plywood for stucco.

Spray polyurethane foam at the necessary 2lbs or higher density for exterior side applications is neither cheap nor green, due to the HFC245fa blowing agent. (Lapolla's 2lb foam is now blown with an HFO1234_ _ variant which is MUCH lower impact.)

For enhancing the wall-R, use sheets of rigid EPS, which is suitable for direct application of any number of EIFS finishes directly on the foam to give it the stucco or adobe look.

The mass effect will definitely enhance the thermal performance in a high desert location with diurnal temperature swings of 40F+. Even though R10.4 would be tough at 0F without the thermal mass effect, in the high desert on nights when it hits 0F it's often 40F or higher less than 10 hours later. The peak 0F load is never directly experienced indoors and the average load is even reduced by the solar heating of the thermal mass. This is very different from say Fargo ND, where a 0F night would typically only rise to 15F during the day.

R10.4 mass walls would meet IRC code for thermal performance in US climate zone 3B & 4B portions of NM, but it would need to be at least R13 in zone 5. Find yourself on this map:

http://cdn2.hubspot.net/hub/88935/file-30568645-jpg/images/iecc-climate-zone-map-energy-code-warm-moist-line-800.jpg?t=1455551268752

Refer to the MASS WALLl R-value column in TABLE N1102.1.1:

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm

If you're in zone 5B an inch of EPS would get you to code min, but it's probably going to be worth going for 2" or more.

I am in 5B for sure.

In zone 5B an interior side 2x4 studwall insulated to R13-R15 would have sufficient dew point control with the R10.4 LiteBlock 38 on the exterior that it would not need an interior side vapor retarder (other than standard latex paint on wallboard), and it would beat code min with margin.

If that's cheaper & easier than a couple inches of exterior EPS it's probably the way to go. Going with 2" of exterior EPS approach would perform about as well as an interior 2x4/R15 wall due to better use of the thermal mass. The EPS approach comes in at about R19-R20 "whole wall R", to the R21-R22 of the insulated interior studwall, but it catches up in average performance from the more optimal thermal mass benefit.

The LiteBlock 38 has nowhere near the thermal mass of a traditional thick adobe wall- they can't really be compared. The thermal time constant of a LiteBlock wall is measured in handfuls of hours, whereas with two-foot thick adobe it's measured in days.