Design Architecture Timberblock Framing Is a Strange Hybrid of Wood and Foam By Lloyd Alter Design Editor University of Toronto Lloyd Alter is Design Editor for Treehugger and teaches Sustainable Design at Ryerson University in Toronto. our editorial process Facebook Facebook Twitter Twitter Lloyd Alter Updated October 11, 2018 Promo image. Timberblock Share Twitter Pinterest Email Design Tiny Homes Architecture Interior Design Green Design Urban Design Timberblock/Promo image A lot of people like the look and feel of log homes, the warmth of wood inside and out, but real log homes use a lot of wood, do not hit very high R values, and as Andrew Michler noted in Inhabitat, they often leak air because of settling (shrinkage) and checking (cracking). Timberblock offers an interesting alternative: They create a sandwich of wood on the inside and out, with polyurethane foam as the filling. It achieves and maintains R-30, which they claim is more than four times the level of insulation in a traditional log home, using a lot less wood. They then take these "logs" and prefabricate them into panels. Lloyd Alter/CC BY 2.0 Like a structural insulated panel, (SIP) you get a continuous wall of insulating foam, albeit with a thermal bridge of wood at the edge of the panels in the corners. There is a lot to like here; R-30 is nothing to sneeze at, and one gets the wood look with a lot less wood. Some of the stock designs are not nearly so derivative as the one shown above. They claim that the polyurethane foam that they use is free of ozone depleting substances. Because the foaming is done in the factory, there are none of the worries of outgassing while curing. Timberblock/Promo image Like all prefab systems, the speed of installation is impressive, and the waste and damage on site is minimal. But I do have a concern about a polyurethane and wood sandwich. I asked the representative about fire safety, and was told that the foam is treated with a flame retardant and the wood with borates. At the joint between logs, the wood is bevelled and gets pretty thin. While polyurethane foam fire retardants are usually chlorinated rather than brominated, and less toxic, I tend to run with the recommendations of Environmental Building News, and avoid combustible materials where feasible, and provide adequate fire separation, not to mention sprinklers. An R-30 wall that gives the log look with only 40% of the wood is a system worth looking at. But there are certainly tradeoffs.