Framing the exterior wall trusses - Part 1.

With the roof now able to keep my project dry and the load bearing structure of the house complete, it was time to turn my attention to "building out" the exterior walls. The extra thickness of these walls comes from the addition of exterior trusses and an interior service cavity. An advantage (in terms of "buildability") of the wall system I am using is that the wall trusses are essentially built "one stick at a time". This allowed me to "pick away" at the framing here and there by myself as time permitted. This post will cover the first steps in the process.

"Building out" the exterior walls was my winter project this year.

First some nomenclature. I will hereafter refer to all the components of the inner (load bearing) structure of the house as "primary", while all the exterior components are "secondary". I'm not sure if there is a better way to differentiate but it can be otherwise confusing when discussing studs and plates if there isn't some means of differentiation.

The first steps in framing the wall trusses were to fasten a secondary bottom plate to the treated plywood mudsill and nail on the gussets. The next post on framing the exterior wall trusses will cover the installation of the secondary studs.

I decided to extend the secondary bottom plate at the main floor level as a "top plate" for the secondary basement studs so a little pre-planning was required to determine the stud lengths. Originally, I had planned to extend the secondary basement studs continuously up to the top of the main floor walls (without an intersecting plate) but to do so requires that the main floor and basement primary studs be in perfect alignment - a condition that did not exist in my case. The gussets were fabricated from 3/4" plywood by first ripping each sheet into 8'x10 1/2" strips, then cross cutting the strips into 6"x10 1/2" gussets. For cross cutting, I used a 12" sliding compound mitre saw. Using this saw I was able to build a jig that allowed me to feed in four strips at once, making the process relatively quick and easy.

The plywood mudsill extends 7" from the rim board assembly. I snapped a chalk line to provide for the 3 1/2" space required between the two rows of studs then layed down a continuous bead of adhesive (PL Premium). Because I had planned to use adhesive for this job, I made sure to get all these plates glued down in late fall - when I still had above freezing temperatures to work with.

I put the plates down on the adhesive, then nailed while straightening the plate along the chalk line. The nails are 2 1/2" galvanized ardox.

Bottom plate to "top plate" transition. Notice I had already installed all the secondary basement studs prior to installing the plate. You can also see here that I used canned foam to close the small gap between the bottom of the foundation insulation boards and the plywood mudsill - it has turned slightly yellow from UV exposure.

The gussets were face nailed to the primary studs 48" o.c. vertically. With the service cavity uninsulated, each gusset represents a thermal bridge across the envelope - but in terms of cross sectional area, these thermal bridges represent a tiny fraction of the thermal bridging through a conventional stud wall with only a single row of studs.

Expectation and the Blues - Corb Lund