Last Updated: Feb 10, 2021
To make your older home more efficient and reduce your energy bills, sometimes you have to look down. In this article, you will learn how I insulated my basement in Halifax, Nova Scotia, Canada, and give you some tips to consider when insulating your basement.
An uninsulated basement in an older home can easily lose 20% of your hard-earned heat energy in winter. According to my Home Energy Assessment, it was a whopping 50% of the heat loss in my own house. My basement heat loss was a higher percentage because I had already improved the insulation in the rest of the house. It was time to dig deep and deal with the basement!
The foundation walls are stone with mortar, and the floor is dirt with a layer of gravel. This basement is relatively dry, with no standing water and no evidence of water running down the walls. The floor drains well through the gravel to a sump pump located in the other corner. Experience shows me the basement does not regularly flood with water, an important point to consider.
Some basements are frequently exposed to water. So avoiding water damage is the most important thing to think about when choosing insulation for a basement. If you have a relatively dry basement like mine, you are fortunate to have a few different options. But suppose your basement regularly has groundwater running through it. In that case, you must make sure your drainage system is sufficient before you install any insulation. Talk with a professional in basement drainage.
Having closed-cell spray foam insulation applied to the entire basement (walls, header, and floor) is the quickest, most effective way to insulate a rough stone basement like mine. I had a continuous 4-inch layer applied in a single day. It’s triple-purpose, providing high insulation value (R-28), sealing all the air leaks around the stones and headers, and stopping dampness and humidity. A layer of closed-cell spray foam at least 2 inches thick works as a vapor barrier.
One catch is you have to leave your house for a few days while the insulation cures. But when I went back into the basement after a couple of days to check it out, the air quality was way better than before the insulation job. There was no more damp, musty basement smell. And it’s so clean down there now!
Dense spray foam like this is hard enough to walk on once it cures. However, you still have to cover it. If it’s in a non-inhabited space, then a fire-retardant paint does the trick. If the area is inhabited, then a protective surface like gypsum board or wood is advised. My basement is not occupied, but I covered it with wood anyway, as you’ll see later.
If you are going to use spray foam, choose a brand of spray foam with a low Global Warming Potential (GWP). I found foam with GWP = 1 (one), the most climate-friendly kind available in Canada.
If your basement is smooth and dry, perhaps with concrete surfaces, you can insulate with rigid mineral wool boards against the concrete. You can then frame a wall and install a new floor over the rigid insulation. Mineral wool is a solid choice in this case because it does not get damaged by exposure to dampness. You can install mineral wool batt insulation in the cavities of a new framed wall.
With this method, it can help to install a polyethylene vapor barrier. Heavy-duty 6-mil poly is best to reduce moisture evaporation into the basement. The wood framing should not be under the vapor barrier because it could get too damp in that position, so install the vapor barrier against the concrete or against the rigid boards.
Once the spray foam was done in my basement, I decided to finish it by building a wooden floor and wall coverings to conceal the spray foam. I included mineral wool batt insulation in the floor and wall construction. I didn’t need to add a vapor barrier because the foam is already a vapor barrier. But, I added a breathable house wrap to contain the mineral wool insulation fibers. The completed floor and walls will have an effective insulation value of R-40, rivaling a top-performing new Passive House.
*The Cost includes $3,700 spray foam installation, $400 prep work, and $1,200 for insulated wood floor and walls to cover the spray foam. With the above calculations in mind, this upgrade will have a payback period of fewer than seven years. After that, it will be making me money!
Yes, insulating the outside of a foundation can be a good approach. This method is especially useful if your basement is already finished - and you don’t want to tear apart the interior work. You can have a contractor dig around the outside of the foundation and add expanded polystyrene (EPS) insulation to the exterior.
Insulating the exterior has advantages, especially because you can damp-proof the foundation simultaneously and solve any drainage and water leakage issues you might have.
One thing that surprised me about the spray foam job was how much overspray there was on everything in the basement afterward. Luckily there wasn’t much equipment down there since anything in the area would have been covered in foam.
I took out the hot water tank temporarily for the job. The contractor taped over the water meter and the main water valve. We covered the sump pump with a protective sheet of plastic, which was wise because the above photo is what it looked like afterward - totally encased in spray foam!
Wayne Groszko is a consultant, researcher, and teacher in Energy Sustainability with 13 years of experience. He has taught at Dalhousie University and the Nova Scotia Community College, in the Faculties of Engineering, Environmental Science, and Energy Sustainability Engineering Technology. Wayne is also President of the Community Energy Cooperative of New Brunswick, and has worked as Renewable Energy Coordinator with the Ecology Action Centre in Nova Scotia. He holds a B.Sc. (Hon.) from the University of Calgary, and a Ph.D. from Dalhousie University.