Insulate an unconditioned workshop in 2A?
I live in central Texas, zone 2A, and use a 10’ x 20’ detached garage as a hobby woodworking shop. I would like to know if adding insulation is a waste of resources.
Right now the shop has no insulation. The exterior is wood. There’s a radiant barrier under the roof deck, open eaves, two passive mushroom vents, a 7’x8’ uninsulated garage door that faces west, and ⅝” drywall on the walls. It’s on a slab.
In the summer I use a fan and cross ventilate by opening both the garage door and person door. In the winter I close everything and stand next to an oil-filled electric radiator.
I would like to make the temperature a little more comfortable. I am planning to insulate the garage door. I am also considering insulating the underside of the roof as a cathedral ceiling. The rafters are 2×6. It’s very tempting to install batts up against the roof deck, but I know I’m not supposed to do that. I’m considering spray foam or vented batts. I don’t have any immediate plans to add an air conditioner, but I may do that in a few years. Is insulating without adding AC or heat a waste of resources?
Another factor is that I plan to add a 1000 CFM cyclone dust collector that I would like to vent outside so the fine dust exits the shop. The vast majority of time it would not be on, but when I use a machine, the dust collector would run for a few minutes and evacuate the whole space quickly. (I don’t have any combustion appliances and I would provide make up air.) My friends who have done this and have air conditioners say that the shop returns to normal temperature relatively quickly.
My thinking is that if I can reduce the radiant heat from the roof that the shop would be more like a cave than a greenhouse. Or is this all moot because the building is not sealed?
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Replies
I'm in south Louisiana, zone 2A. At my old house, I had an uninsulated 2-car garage door that faced southwest. I replaced it with an insulated garage door, and it really made a big difference not to have a wall-sized radiator. The garage would maintain a much more consistent temperature.
Spray foam seems too expensive for an unconditioned space, if the goal for most of the year is to reduce heat gain. Maybe you could block heat by adding EPS foam board under the rafters, so whatever heat comes through the roof would be guided up toward the roof vents, corralled between the roof and foam board. Like a giant baffled vent. This might also be a case where powered roof vents make sense.
Thank you for the reply. That makes sense. This weekend I installed an R-8 insulation kit on the garage door. It took the inside surface temperature of the garage door from about 125F to about 100F. That has to help!