Garage Floor and Drainage — Slope, Cracks, and Water Management

I walked into what used to be a garage on Burnhamthorpe Road last Tuesday and immediately knew something was off. The floor felt spongy under my feet, there was a musty smell that hit me the moment I stepped inside, and I could see daylight peeking through gaps where the overhead door used to be. The homeowner proudly told me they'd converted it into a "bonus room" for their teenager, but what I found most concerning was the complete lack of proper permits or moisture barriers.

Garage conversions are everywhere in Mississauga these days. With average home prices pushing $950,000, I get it. Families need more space and they're looking at that two-car garage thinking it's free square footage. Sound familiar?

Here's what buyers always underestimate about these conversions. That concrete slab wasn't designed for living space. It was poured to park cars on, maybe store some lawn equipment. When you try to turn it into a bedroom or family room without proper preparation, you're asking for trouble.

I've inspected probably 200 converted garages over my 15 years, and the problems are almost always the same. Moisture issues top the list because that concrete slab has no vapor barrier underneath. Cars used to drip water, snow melted, nobody cared if it was damp. Now you've got carpet and drywall soaking up moisture from below.

The electrical work is another nightmare. I was in a house in Port Credit last month where someone had just run extension cords through the walls to power the converted space. No dedicated circuits, no proper outlets, definitely no permits. The insurance company would have a field day with that setup.

But here's what really gets me. Most of these conversions in the 1970s and 1980s homes around Streetsville and Erin Mills were done without any permits at all. The homeowner's brother-in-law did the work, or they hired someone who promised to "keep it simple." You know what's not simple? Explaining to your insurance company why your claim is being denied because you made unpermitted structural changes.

Insulation is typically a disaster too. I've seen people stuff regular fiberglass batts into walls without any consideration for the temperature differential. That concrete slab is going to be cold, especially come this April 2026 when spring weather has those temperature swings we get in Ontario. Hot days, cool nights, and moisture condensing inside your walls.

The most surprising conversion I ever saw was on Hurontario Street about three years ago. The homeowner had actually done everything right. Proper permits, raised subfloor with moisture barriers, dedicated electrical service, even had the HVAC properly extended. Must have cost them close to $24,800, but it was done properly. Guess what? It was the only garage conversion I've ever recommended a buyer move forward with.

Most of the time though, you're looking at cheap fixes that create expensive problems. I inspected one house in Erin Mills where they'd just thrown some laminate flooring over the concrete and called it done. Within two years, that flooring was buckling from moisture. The drywall had black mold growing behind it. The family ended up spending $18,400 just to rip everything out and start over.

Here's my biggest concern with these conversions in older Mississauga homes. The garage door opening gets filled in, but rarely properly. I've seen everything from plywood sheets to mismatched brick. The structural integrity of that wall becomes questionable, especially if they've removed the header beam or modified the framing without engineering approval.

Then there's the foundation issues. Those garage slabs weren't poured to the same specifications as house foundations. They crack, they settle differently, they weren't designed to support interior walls. I've seen conversions where the floor has actually sunk in corners because the fill underneath wasn't properly compacted.

Don't even get me started on the heating and cooling. Most people just throw in a baseboard heater and call it done. No consideration for proper air circulation, no connection to the main HVAC system. Come summer, that converted garage is going to be sweltering. Winter hits, and you're looking at heating bills that'll shock you.

The permit situation drives me crazy because it's so preventable. In Mississauga, you absolutely need permits for this kind of conversion. Building permits, electrical permits, probably HVAC permits too. When I find an unpermitted conversion, I have to recommend the buyers budget for bringing everything up to code. That's typically $15,000 to $28,000 if you do it properly.

I was in a house last week where the converted garage actually had water stains on the ceiling. The roof structure above hadn't been modified to handle interior finishes, and ice damming was causing leaks. The seller had no idea because they'd just painted over the stains each time.

What really bothers me is when families put kids in these converted spaces without thinking about safety. Proper egress windows, smoke detectors tied into the house system, carbon monoxide detection. These aren't nice-to-haves, they're life safety issues.

The good news is that when garage conversions are done right, they can work. But in 15 years of inspections across Mississauga, I've seen maybe five that I'd call properly executed. The rest are problems waiting to happen.

If you're looking at a house with a garage conversion in Mississauga, make sure your inspector knows what to look for. The real issues are often hidden behind those fresh walls and new floors.