Curtain Trusses with Cellulose Insulation for a Timber Frame

Many timber-framers are aware of the problems with CFC-based foam insulation but continue to use urethane-core stress-skin panels because they haven’t found a better alternative. Well, here’s a technique adopted by a Massachusetts builder for low-budget timber frame homes. The technique involves site-fabrication of a type of curtain-trusses—2x2 ladders that hang on the outside of the timber frame to contain the insulation. (The term “curtain truss” was coined to describe this generic type of wall system.)

There are many variations to this technique employed by timber framers across the country. The trusses can be made to any depth desired, though most are 8 to 12 inches, for insulation values between R-28 and R-42. They can be made with plywood webs or gussets, instead of the 2x2s employed here. And they can be used on the roof as well, providing deeper insulation cavities than standard rafters. Although many builders use fiberglass, the ideal insulation material from an environmental standpoint is cellulose, which is made out of recycled newspaper. When blown into the cavities at a high enough density (3.5 lbs. per cubic foot) settling has not been a problem.