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What You Need to Know Before Renovating Your Basement

What You Need to Know Before Renovating Your Basement
Interior of bungalow style city house in Toronto, Canada. This is a 80 years...

Mike Holmes is one of HGTV Canada’s go-to contractors and the host of Holmes and HolmesHolmes: Buy it Right and Home to Win.


A basement renovation is one of the most popular projects that homeowners undertake. Done properly, a basement reno can add value to your home as well as add extra living space. Doing your homework and finding the right contractor is a must, but there are other things you might not be aware of when it comes to creating your dream space downstairs.


Some homeowners still overlook the importance of getting municipal building permits when doing a basement reno (or any home renovation). The building permit is your insurance that the job is done properly and up to code. A good contractor will know that permits are required but don’t rely on your contractor to get them; the responsibility is with the homeowner.

Many homeowners believe that getting permits is just an added hassle and a cash grab. Yes, it’s an extra step that you have to take before starting the work but trust me – it’s worth the effort. If there’s ever an insurance claim related to work that has been done on your home, you may be at fault in the absence of a building permit. Let’s say you have an electrical fire in your home; the Fire Marshall’s office, along with your insurance company, will conduct an investigation to get to the root cause. If the electrical work was done by a shoddy electrician and no inspection was done to certify that the work was up to code, then the blame lies with you, the homeowner.

Permits for a renovation are also important when it comes time to sell your home. Potential buyers may contact the municipal office for proof that the work done on your home included a building permit and final inspection by a municipal building inspector. If permits were never obtained, or if the permits remain open and the final inspection was never done, I’d advise any potential buyer to walk away.


Walls Are Not Square and Plumb

Basement walls are never square and plumb, so don’t be discouraged if your basement walls don’t look perfectly straight and aligned. Framing is where the proper measurements are done. Your contractor will make sure that the framing is square, plumb (vertically aligned) and level (horizontally aligned). Crooked framing will result in walls and trim that will look wavy and uneven; plus make shelves and cabinets difficult to install; all the more reason to hire a pro who knows what they’re doing.

Related: This is How to Properly Frame a Basement, According to Mike Holmes

Closing in a Furnace Room

The area in your basement that houses your furnace and water tank should not be part of your basement renovation. This area should be kept separate with adequate space and proper ventilation. Homeowners want to maximize the livable space in the basement when working on their design plans, but space for your furnace and water heater to have sufficient combustion air to breathe, and for maintenance work to be done, is very important. Proper ventilation is key to circulating air efficiently and also for fire prevention. Most furnace rooms should have one vent at floor level and another vent at ceiling height. A certified HVAC professional will ensure that the furnace won’t “choke” and that vent sizes are adequate.


Wood and Concrete

The concrete foundation and floor of your basement, no matter how long ago it was poured, still contains moisture. Concrete is porous, so your home’s foundation will always absorb water from the exterior. For this reason, the wood framing in your basement should never touch the concrete foundation. The moisture from the foundation will seep into the wood, causing the wood to rot and deteriorate. A sill gasket should be placed between the concrete and the wood framing to prevent moisture from seeping from the concrete. Your contractor should know to add this moisture barrier when framing.

Proper Insulation

Failing to properly insulate your basement is just asking for mould and mildew problems. Your unfinished basement is probably like most unfinished basements out there – the pink wall wrap insulation covers the top half of the basement wall. Most contractors would probably say that’s OK because the temperature below the frost line stays pretty constant, but that’s not the case. The floor temperature is fairly constant, but as you go up the walls to the ceiling, the temperature rises. So the temperature near the ceiling of your basement is always warmer than the floor.

Ideally, you’ll want to remove the pink wall wrap insulation entirely and have a new insulation and vapour barrier system installed, or a spray foam application installed from floor to ceiling. Insulating your basement this way creates a thermal break between the warm air inside and the cooler air outside, preventing condensation and moisture build-up. Spray foam insulation is also mould and mildew resistant, which is an added bonus. You’ll also want a thermal break in your floor. A membrane, like Schluter Ditra is a great thermal break beneath a tile floor. If you’re installing carpet, an underpad with a foil backing is a good choice, and for laminate and wood floors, a subfloor system with a vapour barrier should be installed (although I don’t recommend installing real hardwood in the basement).

It’s important to do your homework when considering a basement renovation. Yes, researching the right contractor is important, but you also want to be aware of what is required. Know what your contractor is doing and why. I always tell homeowners to test their homes for radon before the renovation. If you discover high levels of radon in your basement and need to mitigate it after the reno, it will cost you much more.


Do your research and ask questions. Make it right the first time so you don’t have any costly regrets.

Images courtesy of The Holmes Group, Getty Images and Harmony Home Builders

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