Was going to write this response back as a comment responding to Brian and Deirdre’s comments from earlier today/last night, but figured there was enough here that it would make a better post.
The whole topic of wall construction/insulation has really been one that has spurred a lot of conversation and thought both here and at the different forums that are following my posts.It seems, the more I learn the more I question if building a home the traditional 2″ x 6″ ways is really what’s right.
I keep being drawn back to the 12″ wide double studded construction method, especially after seeing it firsthand at Brian’s house. For those of you who don’t know what I’m talking about, check out this New York Times Youtube video about an affordable green housing community by the Planet Green Group. This framing method is a centerpiece of their very green/affordable project.
Business: Home Green Home: Affordable Green Living -NYTimes
Basically, the wall is constructed with an outside 2″ x 4″ wall that is separated from an inside 2″ x 4″ wall with a 4″ air gap and then the entire combination is filled with cellulose.Might sound like a bunch of extra work and materials, and it definitely is some, but it eliminates the majority of the green deficiencies of a conventional 2″ x 6″ wall.Energy efficiency is dramatically increased through the additional width of the wall and eliminating the bridging losses caused by the contiguous span of wood.Wood material might increase, but for a wall with foam on top of the exterior sheathing (as specd in this project) you would eliminating a significant amount of 4′ x 8′ boards of 1″ rigid foam.For this project 90 boards at a cost of $1,700 would be eliminated; something that should go a long ways towards paying for the extra wood and cellulose insulation.Another positive side effect is replacing foam, which is a not so green product in my mind (being petroleum-based and all) with recycled paper.Seems like a win, win to me.
Add to this whole discussion the new IECC Code that Brian mentioned that will be adopted by Maine this month and the reasoning for a better wall is even more obvious.
The 2009 IECC code rates Aroostook County as a more severe climate zone than the rest of the state.Guidelines for this code is the following required insulation levels:
- Ceiling: R-49
- Wood Framed Wall: R-21
- Slab: R-10
On paper, all components of our specd home will meet these requirements, with many saying a 2″ x 6″ wall 16 o.c. with 1″ blue is R-26, but if you take into consideration the heat bridging across the studs and windows/door headers the wall quickly has a real world insulation value of less than R-20; not exactly where I’d like to start things out.
So, the next thing I need to figure out with a calculator and spreadsheet is how much materials a double-studded wall would add, and then what complexities/additional labor it would require.
Any ideas from you builder folks?