Green insulation in between two-by-fours

How to insulate your basement

This is Lesson 4 of our informal online course: Home Energy 101All lessons by Philip Drader.

After you’ve resolved any moisture issues in your basement, you can start planning what you are going to do in your basement. Before you do, here’s one more note of caution.

Deal with foundation problems first

All of the following advice is given assuming you have no structural issues to deal with on your foundation. Do not insulate or finish your basement until you have all structural issues dealt with appropriately.

A crawlspace is a tiny basement

You might think you have a crawlspace instead of a basement. You don’t have a crawlspace: You have a really short, uninsulated basement that you should insulate. So yes, this advice applies to your home too.

How much insulation is enough?

With current energy prices, it can be tough to justify any more basement insulation than R22 or R24, which both require 5 1/2″ of space. I’m assuming that batt insulation will be used since it is the cheapest for a given R-value, though if space is a constraint, rigid insulation might save some room.

If you are concerned with your carbon footprint, you may want to go beyond the minimum insulation to see maximum financial savings and strive for a home with net zero energy use. For example, the REEP House for Sustainable Living which is a near net zero house has R38 insulation in its basement. If you want to reduce your carbon emissions, you’re better off making that investment in something like solar panels.

Three basic options for insulating a basement wall

1. The cheapest method overall is to use a roll-blanket, power-nailed to the concrete wall, which doesn’t require you to ‘finish’ the space, but can give you good energy savings.

2. If you plan to finish the space, the cheapest method is to use metal studs. There is a substantial cost difference from the roll-blanket method as it involves putting in electrical boxes, lights, doors, drywall, paint, and trim. If you use metal studs, you’ll want to put insulation behind it, between the concrete wall and the stud, to prevent thermal bridging from cancelling all the benefits of the insulation between the studs. Thermal bridging occurs when poor insulating material (such as the metal studs) allows easy pathways for heat to flow through your insulated walls.

3. Many people finish their basement using wood studs (see photo at top), which tends to take a bit longer to install, but it has a reasonable insulation value when compared to steel studs. And more importantly for a lot of people, they can support the weight of a large TV without concern.

Whatever method you choose, a critical consideration when renovating a basement is to make sure that water pipes will have insulation behind them, or they might freeze.

duct top takeoff illustrationAnd finally, if you are planning on finishing your basement, seal as much of your ducts for heating, ventilation and air conditioning and pipes as you can access. Use an aluminized-tape for this purpose, and don’t forget the top takeoffs (used to tap into the top of the main trunk duct). as they are the leakiest culprit.

Tips on finishing your basement

Looking for more information about how to finish your basement? Here are the slides from a presentation I made that shares design considerations and other tips.

Learn more

CMHC– Green Renovations: Basements

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