Questions about the Larsen Truss for retrofit applications
Using a Larsen truss system to retrofit an older home for increased wall insulation seems to have at least 2 primary benefits:
1. No foam insulation required, if you think that is an issue.
2. The ability to increase insulation without producing a vapor impermeable exterior wall surface. This could be a big benefit for a home that has an interior poly vapor barrier, and you don’t want to disturb the existing sheet rock, etc.
3. Reduced thermal bridging across the wall structure, again without a foam layer.
A few questions I have…
What other benefits have I left out?
Are there any reasons in particular that a truss system is used, besides to increase cavity thickness? For instance, consider a 2x4 walled home. To produce a wall that has a similar R value as adding 2 inches of foam sheathing to the exterior, would only need approximately 3 to 3.5 inches of densepack cellulose. Would there be any benefit to building trusses, and not using a solid strap, to achieve that size cavity? The truss would reduce thermal bridging over a solid strap, but the solid strap could be spaced to alternate with the existing wall studs.
Are the trusses attached to the existing sheathing, or only hung from the roof rafters, and stood in the bottom plate extension? If attached to the wall, are they aligned with, and attached to the studs, or just attached to the sheathing?
Posted Tue, 02/09/2010 - 10:45
Other Questions in Green building techniques
Since drywall has a permeance of 0.02 liter/sec - m at 75 PA is ever possible to have sheathing dry to the interior of the home?