Is an insulated concrete wall system a wise choice for a low-energy home?
Normanm
| Posted in Energy Efficiency and Durability on
I am interested in building a home that requires very little energy to operate. I was introduced to a insulated concrete wall system,… (Thermomass — http://www.thermomass.com)… which unlike the conventional ICF, where the thermal properties are on the exterior surface, they are internal — a solid foam core sandwiched between 4″ inner and outer layers of concrete.
My thoughts were that durability, air permeability, bulk moisture and thermal comfort would all be addressed in such an application. (Aside from the fact that make-up air would have to be installed anyway.)
Can you add any comment to this?
Thanks
Norm
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Replies
Norm: First, I am not one of the pros here. Are you thinking of building the whole house with Tmass walls? Have you run the numbers on the cost vs double wall construction with dense packed cellulose? Or the REMOTE wall system? Or Riversong/Larsen Truss? Those look like a great system for a foundation wall (I think Riversong likes them a lot), but above grade I would guess they are awfully expensive.
Norm,
If this system limits the insulation to 4" foam at the wall center, that would be R-20 with XPS. It might make sense for a basement wall but probably not for above grade. Depending on your climate you may need R-30, R-40 or more to consider this a "low energy" home. Consider also that embodied energy could be much higher with concrete than with frame walls. XPS insulation has the disadvantage of very high global warming potential due to its blowing gas.
Norman,
I agree with John and Thomas. For above-grade walls, the Thermomass system is too expensive, has too low an R-value, and uses foam with a high global warming potential.
Thank you all for your feed back on the Idea. I wanted to put it out there before we got to deep into the design.
Thanks again
Norm,
We built a system exactly like you describe, for an engineer friend. I repeatedly told him clay is warmer than concrete, but engineers like things that are hard and strong not soft and durable. So we used standard concrete forms and built the 2 story slab on grade house in 3 lifts. The foam was held in place with the reinforcing ties. This house has lots of southern glass, radiant floors and a mod con boiler. The house is cold. My 1903 3-layer adobe with no wall insulation has lower utility costs. Wood and mud are the greenest, best building materials. When you build with wood, you are sequestering carbon for the lifespan of the house. Though I have not actually built one, I really like Robert Riversong's chord truss design. It seems to achieve everything we are looking for reasonably well.