Basement renovations start with waterproofing

Lowering your basement floor requires careful underpinning of the foundation, in stages, to prevent the walls from collapsing and destroying the home.

When we first started putting basements under houses, the space was mainly used for storage, laundry and as a place to keep the furnace and hot water tank out of the way.

But as our lifestyles have changed — and property values rose — the basement became an obvious place to add more living space.

But basements are also the parts of houses that are most likely to get flooded. So the first consideration before starting any work on the basement is to make sure it’s properly waterproofed.

With many older homes, there’s virtually nothing to stop water from seeping through cracks and gaps in the foundation and cause all sorts of problems.

Ideally, you’ll want to do it from the outside, by digging a trench around the entire perimeter of the house and then installing a waterproofing membrane to the exterior side of the wall. Of course, with many city homes, there simply isn’t room between neighbouring houses to excavate. In that case, you’ll need to apply the waterproofing membrane on the inside of the walls.

Either way, the membrane will extend below the floor level and get tied into a weeping tile system that collects any water and channels it away from the foundation.

If you’re adding the waterproofing on the inside, you will need to install a sump pit where the water will collect and, once it reaches a certain level, a pump will push it outside. (Note that the building code prohibits the sump pit from being connected to the sewer lines, so you’ll need an outflow pipe to the exterior.)

In the past few years, we’ve had some torrential storms that taught many homeowners a painful lesson. When does the power tend to go out? When there’s flooding. When do you most need your sump pump? When the power’s out and it starts to flood.

I’ve recently come across a great product that helps avoid this catastrophe, the Ion Genesis. It has dual, digital water-level sensors so there’s a built-in backup. It can be combined with a battery backup to keep the system running when you need it. There’s even an alarm system that will automatically call you if there is a problem.

Most older basements have little to no headroom, so before renovating, owners often opt to excavate first. There are two basic options: underpinning and benching. With underpinning, a contractor will excavate below the existing foundation wall, in stages, and then pour a new, deeper foundation below the original.

Benching involves breaking up the floor and pouring a new foundation adjacent to the existing one. Benching is cheaper — it might cost about $40,000 to underpin a 500-square-foot basement; benching would be about $25,000. But for each foot you go down, your new foundation has to project a foot out from the existing wall. So you end up with a “bench” around the perimeter that eats into the usable floorspace.

Whichever route you take, you’ll want to use a reputable, experienced company that has all the proper licences and insurance. (Last year, a house near Avenue Rd. and Lawrence Ave. collapsed while being underpinned and a 19-year-old working on the project was killed.)

Breaking up the floor has the added advantage of allowing you to install new sewage pipes, and make other modifications, such as installing a backwater valve. This device prevents water from municipal sewer lines from getting into your home if there’s a backup. The City of Toronto has a rebate program that covers up to $1,250 of the cost of installing a backwater valve.

You might also want to consider adding radiant (hot water) heating or electric heating cables below the floor to warm the space. Or, if not for the entire floor, at least in the bathroom if you’re adding one.

The layers of gravel and insulation that will go down before the new concrete floor is poured also act as a barrier against radon, a naturally occurring radioactive element in the soil that’s found in potentially dangerous levels in some parts of the country.

Obviously, you’ll need to insulate the walls if that’s not already done. The tried-and-true method is to install batt insulation between the wall studs, then cover it with a vapour barrier and drywall. Another option is prefab panels that include framing, insulation and a finished interior wall all in one.

Finally, if your plan is to create your dream home-entertainment centre in the basement, I’d recommend you soundproof it from the rest of the house. Adding insulation in the space between the ceiling and floor above will help muffle the sound from blockbuster movies. I use Owens Corning’s specially designed QuietZone acoustic insulation for this. Finish it off by mounting soundproofing drywall (or doubled-up sheets of regular drywall) on “resilient channels,” metal strips that help reduce sound transmission, and you’ll be able to enjoy movies and music without disturbing the rest of the house.

Source: Toronto Star

Jim Caruk’s column runs every two weeks in New in Homes & Condos. He’s a master contractor, editor-in-chief of Renovation ContractorEND magazine, renovation editor for Reno & Decor ENDmagazine, and founder of the Renos for Heroes program and Build It Yourself Learning Centres in the GTA.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: