Details for a “High-Performance Garage” – GWC Mag

A few years ago, my husband and I completed what we like to call our “high-performance garage.” While those two terms may seem at odds with each other, we found that the insulation and air-sealing measures we employed go a long way toward making up for the poor performance of a typical garage door—notorious for air leakage. Because this detached garage is more of a workshop for us, we wanted to increase performance enough that the space would be comfortable to work in, even during the coldest Wisconsin months.

The assemblies

The first thing we did was plan for 2 in. of foam and a vapor retarder below the slab. This not only reduces heat loss to the ground, but also helps the slab hold onto any heat it absorbs through radiation and conduction. (The only mechanical equipment in the space is a 5000-watt electric-resistance heater but the slab holds on to heat better than the average garage slab because of the insulation below.) We ran the foam and the vapor retarder up the concrete side walls and broke the thermal bridge between the slab and wall. It was simple and easy to do and well worth it for the performance impact.

For the above-grade walls, we used a Larsen truss assembly. We chose this wall system because we wanted a nice thick layer of insulation in the walls and the roof, and it was less expensive to thicken the walls with 2x2s and plywood gussets than it would have been to install exterior foam—with all the fasteners, furring strips, exterior jamb extensions, etc. And for the ceiling, we would have needed a crane to set the trusses, had we gone that route.

Using plywood scraps and 2x2s we created an 8-in. thermal bridge–free cavity inboard of the…