We have talked to several builders in San Antonio Texas area about an ICF home and they all seem to think that for this climate ICF walls are not worth the extra cost.   The attic  insulation is what really matters.   We are now considering building with an unvented attic with spray foam insulation on the roof.  Then framing using the  advanced wall framing method  with  2x6 24" oc with spray foam insulation and using the EFIS stucco exterior finish.      I know that in the past there have been moisture issues with EFIS.   Is this still the case?  Are some manufacturers better than others.

Anyone care to comment about using ICF's in this climate?

If the home will be built in a heavily termite infested area, then the EIFS should be at least 6" above the finished grade.

If ICF's is overkill, then have you looked at SIPS?  Less cost and the insulation level can be dialed in to whatever you want.

I looked at EIFS and passed. While the major systems like Dryvit have worked out all the bugs, installation is key. If your installer doesn't do the windows right, you will have problems and likely the manufacturer won't help. Some insurers won't cover EIFS. Calling your insurer would be a place to start. My engineer came to the same decision. He went ICF. I went AAC (equivalent to hybrid ICF.) If you decide on EIFS, pick a major system and ask the distributor to recommend installers.
There is a third option for a stucco look: cement fiber board. I had a small area on the second floor where stud walls were required. I covered them with Hardie panel, (~$33 a 4x8 sheet) and from ground level it is hard to tell the difference.
If you have a wild and crazy streak, Nichiha has some very intriguing siding options (nichiha.com) although they are not cheap.
Near as I can tell, cement fiber board is paper soaked in cement and pressed into a sheet. Keep the edges dry and it will weather like, well, cement. Better actually.
Weight is the only hitch. It is super heavy, and drainage planes and exterior foam will require some thought. And muscle. I have a two foot overhang on my house. I thought hardie panel soffets would be the death of me.

Did you put a skim coat or synthetic stucco over the Hardie panel or just paint?

Neither yet. The stucco guy starts next week. We will paint it first and see how well it matches the old world (mottled) stucco finish. There is very little adjacency so it is worth a try. The stucco guy said he'd want mesh under it, painted or unpainted.
But to complete the loop, skim coat over hardie panel would add $4+/sf in my case to the $1+/sf for the panel, or a tad less than than stucco over AAC, and one suspects, less than EIFS in most markets as well. Your costs will vary. That said, if paint doesn't do it, I'd want to read what hardie says warranty wise before moving on to stucco.

Posted By calvinml on 06 May 2011 03:48 PM
We have talked to several builders in San Antonio Texas area about an ICF home and they all seem to think that for this climate ICF walls are not worth the extra cost.   The attic  insulation is what really matters.   We are now considering building with an unvented attic with spray foam insulation on the roof.  Then framing using the  advanced wall framing method  with  2x6 24" oc with spray foam insulation and using the EFIS stucco exterior finish.      I know that in the past there have been moisture issues with EFIS.   Is this still the case?  Are some manufacturers better than others.

Anyone care to comment about using ICF's in this climate?

San Antonio is hot enough with big enough temperature swings to benefit from ICF, but it's not enough of a performance boost to rationalize the additional cost.  AF 2x6 and an inch of exterior foam would outperform it. But ICF is a lot more resistant to wind events like hurricanes (and quieter.)  ICF is a great way to build, but the energy efficiency boost would only be a secondary consideration.  A hurricane might take your roof off and blow the windows out, but the walls would be pretty much un-fazed.

From a best use of thermal mass POV, the same amount of concrete fully inside the insulation rather than in an EPS sandwich can have nearly twice the benefit in hot climates.

But, a minimal ICF has a whole-wall R of R16.

A 2x6AF studwall with oc foam cavity-fill after factoring in the thermal bridging of the framing comes in at R15- similar, but slightly less.

If you went with closed cell it might edge out the ICF for steady-state R, but still underperform the minimal ICF.

But an in inch of XPS over the oc foam studwall brings that up to R20, a 33% boost in whole-wall R value, and that would beat the R16 ICF in thermal performance.

If you saved the foam budget for exterior XPS, and used wet-spray cellulose in the stud bays rather than oc foam you'd have the same R20 for similar money as an R15 foam-filled studwall.  An inch of XPS on the exterior also puts a ~1-perm vapor retarder between the structural wood and the EIFS, and is protective of the wood.  Flashing details and material selection around windows & doors would still be critical though.  The cellulose also has a measureable amount of thermal mass, comparable to adding another 3/16-1/4 inch of thickness to the interior gypsum.  That's enough of a difference to measure (in a test lab) the performance difference between oc foam & cellulose in climate like San Antonio but it's an order of magnitude less than an ICF.