Alternative Building Systems Burlington VT
South Burlington, VT
St. George, VT
Affordable, Site-Built Homes
Alternative Building Systems
How do various alternative building systems compare in price and performance?
Question: How do Rasta block (a concrete form system), aerated autoclaved concrete (AAC) and Durisol (blocks made from recycled wood) compare in price and performance? Performance criteria can include insulating value, structural strength, resistance to termite burrowing, resistance to water, vapor permeability/breathability and anything else you can think of that matters. I'm also interested in comparison of those materials with the Strata International Group's insulated composite described in your May/June 2006 edition, though that product may be too new for good price data. Thanks for any advice you can offer.
Answer: The confusion between nominal, clear-wall, whole-wall and dynamic R-values illustrates the problem of comparing building wall systems. What is needed is an apples-to-apples testing program by an independent agency. The closest approximation to date is that of the Oak Ridge National Laboratory's (ORNL) Building Envelopes Program.
ORNL has tested the whole-wall R-values of a number of wall systems, including conventional wood frame, steel frame, log, adobe and earth blocks, structural insulated panels (SIPs) and insulated concrete forms (ICFs). To view the results, log on to http://www.ornl.gov/sci/roofs+walls and click on Hotbox Test R-value Database. However, with dozens of ICF products on the market, ORNL will never be able to test them all.
The next best source I know of is Supplement D-1 of the Washington State Energy Code (download at http://www.energy.wsu.edu/ftp-ep/pubs/code/bfg/2004/SupplementD_2004.pdf ), which lists the whole-wall R-values of 19 different ICFs.
Unfortunately, the extremely complex nature of heat flow through walls and roofs, which depends not only on the insulating property of the insulation fill but also on the air-leakiness, the presence of heat short-circuits such as framing and rebar, the amount and location of mass, and the local climate, allows for dubious claims by zealous proponents of any system. My advice is to take any and all claims by manufacturers with a heavy dose of skepticism and rely instead on the experiences of as many customers of the product as possible.
Any system approved by your local building inspector will prove structurally adequate. Any product containing wood fiber may be a target for termites, however. You can ensure an adequate interior vapor barrier (necessary in heating climates) simply by priming the interior surfaces with vapor barrier paint (any paint with a perm rating of 1.0 or less).
Cost comparisons are meaningful only when they include labor. Ask manufacturers for the names of contractors experienced in the use of their products. And, as always, get at least three estimates with stipulations on maximum allowed cost overrun.