I was visiting with an accountant today regarding the 45L Tax Credit. I pointed out the differences between HERS 85 for Energy Star and the 50% reduction of heating and cooling for the 45L program.
He asked what you could do to improve the walls, "2x6"? I described 2x6 plates with offset 2x4s and the concept of basing everything on the 2 foot multiples.
What other concepts are out there for building the envelope? Rigid foam then sheathing? Other types of walls? ICF's etc?
I have come from the custom home building side and we built extremely tight homes in So. Cal. First, your climate zone is important to what you should be using. The ICF or SIPS are very expensive and you can get similar results using everyday items. You can go green or go extreme green. That depends on the client and their budget.
I build with 2x6's, 24" oc and air real well, especially around plumbing and electrical . I use bibs and spider/cellouse. look at homes that have aged 100+ years what are they made of ? New technology is great but is costly
There are many types of walls that are being used, and depending on the region, each one has it's benefits.
In mixed climates, like South Carolina and Georgia, a recently popular material is the aerated autoclave concrete products. HEBEL makes a variety of different products, including wall panels and standard solid blocks. These have thermal mass characteristics, high R-values, are made mostly of sand, and can be recycled.
A great method method of construction to increase R-value, that is also used mostly in cold climates, is PERSIST. Essentially, this is a build-up of layers of rigid insulation on the outside of the buildings exterior framing. In fact, it is attached after the sheathing. Not only does this method provide high insulation values, but it protects the structure, by keeping it dry and at the proper temperatures.
You mentioned ICF. A real good example of that, and one that is known as the first of it's kind (since 1972), is the RASTRA block. It has great acoustical and thermal properties, but it's also made from 85% recycled materials and is 100% recyclable. And, it's affordable, to boot!
I would be remiss if I didn't mention SIPS. Allison Bailes built his home with these panels in 2001, and has been a true believer since. They are typically 4'-0" wide panels of rigid foam sandwiched between OSB. They can be used for floors, walls and roof. They save on labor time, and have great thermal properties.
The opportunities are endless, and depending on the budget and climate, there is an ideal method and/or material.
How about spraying on or rollering on the envelope?
I have 25 years working with a radiant barrier roof coating, an Energy Star 'Cool Roof' coating. We have proven it's effectiveness as an energy saver on roofs and are never questioned there. However, in all these years I have dealt with maybe two dozen architects. They have no problem with us as a roof coating. As soon as we tell them it is also used as an interior / exterior paint for walls and ceilings, you can hear them hit the floor when they fall off their chairs. Only two would spec us in for walls and that was at the insistance of local officials. The architects would never seem to want to 'Step out of their comfortable boxes' with this idea. I have heard statements like 'Energy Star does not recognize wall coatings or paint. I can't specify this, I wont do it, Noone else does it so I am not either".
Them I say the following; "We earned the Energy Star as a 'Cool Roof' coating and you have no problem specifying us for roofs. Now I put it to you; what type of heat gain / loss are we fighting on the roofs?" "Radiant heat" was the reply. "If the same roof coating is applied to the exterior walls, are we not fighting that same radiant heat energy of the sun on those walls in the hot months too?"
The 'Envelope' can be created by coating the entire exterior of a building. This puts the insulation on the outside where it should be An even MORE effective envelope can be created by coating the interior walls and ceilings of a building.
Our coating is an encapsulant material as well as a conductive and radiant heat barrier..