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Renovation & Design

Creating a year-round workshop

How to convert an uninsulated area into a comfortable space

Jean Levac / Ottawa Citizen files

Creating a garage into your dream workshop requires proper insulation, air sealing and ventilation to prevent moisture issues and to make your workspace as comfortable as possible.

Question: I live in one of the newer developments in Winnipeg. I believe the house was built in 1996 or 1997. I am also a hobbyist woodworker, so I have left the basement unfinished and use it as my workshop.

I am a big guy and after driving inexpensive subcompact cars all of my life, I finally broke down and bought a big-ass truck, but it is too long to fit in the garage. So now that the garage is not needed for parking, I am thinking of using the space for my workshop and eventually doing something with the basement. But I am not sure what should be done with the garage to make it a comfortable, warm space in the winters.

The garage is your typical double and has two-by-four construction for the walls. Obviously, I will need to insulate it, but my question is how?

Would there be any advantage to building out the walls to two by six to accommodate thicker bat insulation or could a spray foam application accomplish the same R-value?

What should I be looking at when closing in the attic space and insulating that area?

Also, do you have suggestions for heating? I am a weekend warrior when it comes to the woodworking, so the space does not need to be warm all of the time, but I also do not want to wait for hours to get the frost off of the tools. Actually, I would never want to see frost on the tools as I have a lot of money invested in my toys.

What suggestions do you have for converting a garage into a workshop that can be used year-round? — Shaun Tyler

Answer: Converting an uninsulated area, like your garage, into conditioned space does present some challenges, but should not be that difficult if you pay attention to detail in two main areas. Air sealing the walls and attic and adequate ventilation for the attic space may be the two critical points of reference to preventing future problems. Both of these can be addressed when insulating the garage prior to heating.

The main issue to address when changing your cold garage into a heated shop is prevention of warm air intrusion into the walls and attic. Also, trapping stale, damp air in this space may cause some moisture issues, but that could be addressed with a good exhaust fan, as well. There may be several ways of preventing warm air from leaking into the critical areas, but building out your walls to the thickness of two-by-sixes to accommodate thicker batts may not help in this endeavour. It will lower your heating bills, but the same issues with air sealing will be present whether you have four-inch-thick batts or six-inch.

I would propose an alternative method for the walls, which would not require firring out the current studs. You could install typical fibreglass or rockwool batts in the current wall cavity, but instead of more wood and thicker batts, install a five-centimetre layer of extruded polystyrene (XPF) on the inside of the studs. This could still be covered by a layer of six mil polyethylene to air seal it, but if you do a good job of sealing the overlapping joints of the foam sheets and taping all seams and edges, you may forgo the poly. Once installed, this will not only give you a slightly higher R value than thicker batts, it will give you an adequate air/vapour barrier, as well as a good thermal break between the wood studs and the heated shop air. Drywall, OSB or other sheathing could then be fastened over the XPF with longer screws directly into the studs.

I would also suggest OSB, plywood, or other moisture resistant sheathing, rather than drywall, as it would not be as easily damaged if water was present on the shop floor or from condensation on windows or doors. This may not be possible for all the walls if your garage is attached to your home, because of fire code requirements, but that could be addressed as necessary. If drywall is chosen, ensure to leave a gap above the garage floor or grade beam to prevent wicking moisture from the colder concrete to the sheathing.

As for the attic, installing a well-sealed layer of six mil poly on the underside of the ceiling joists or trusses may be the key to success. This sheathing should be sealed along each ceiling joist, and all overlapping areas, with acoustical sealant to prevent holes in the membrane from fasteners. Installing plastic boots around any electrical boxes or other penetrations will also be needed for a good air seal. Taping any other areas where there is a breach of the poly sheathing with plastic tape will also be required. Once complete, drywall or other sheathing could be installed to finish the ceiling.

The next piece of the puzzle is to install good quality insulation in the attic. The most cost-effective choice may be blown or poured-in cellulose fibre insulation. This could be poured or blown in by you with a rented blower or installed by an insulation contractor. Framing and installing a well-insulated and weather-stripped attic-access hatch will let you to do the insulating yourself and allow for future access, if needed. The next item is to ensure you have adequate roof and soffit vents, which could be installed prior to insulating by a reputable roofer and/or insulation contractor. Finally, heating can be easily done by installing electric baseboards or wall-mounted units that can be regulated with a good quality thermostat, to keep the temperature at your desired level.

Changing your unheated garage to a conditioned shop may not be difficult, but attention to proper insulation, air sealing and ventilation should prevent serious moisture problems and ensure a comfortable workspace, at the same time as keeping your heating bills in line.

 

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com

 

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