Choose the right subfloor system

Choose the right subfloor system

Choose the right subfloor system

Last week I talked about engineered hardwood floors, and one of the big benefits is that you can install them over concrete and below grade, like in a basement. That’s according to some flooring experts, but I think you need to be careful.

If I were going to do this I would add an extra layer of protection to make sure I have the right subfloor system to prevent mould and water damage.

Concrete is porous, and if we’re talking about the basement floor then eventually there’s going to be some moisture coming through the concrete slab.

So it’s important to make sure that: one, moisture doesn’t damage your flooring; two, moisture can dry out once it gets inside; and three, we prevent mould. To do that we have to incorporate the right products and materials.

Some flooring manufacturers might tell you that as long as you put down a six-millimetre plastic sheet barrier on the concrete floor, you can install any type of flooring on top — even real hardwood.

First, I don’t recommend real hardwood flooring in the basement. The risk of moisture or water damage is too high and hardwood costs too much. Even if you had the money to replace your flooring it’s a huge waste of materials and a natural resource.

And the problem with putting a layer of plastic over concrete is that any moisture that penetrates through will be trapped underneath the plastic. It won’t be long before surface mould starts to grow. Your floors might be safe but your health might not, and any mould issue that isn’t fixed grows into a bigger problem — along with the health risks.

Now we have new products and materials made specifically for installing flooring over concrete and preventing mould, like Amdry Insulated Subfloors.

This product comes in panels — one side has foam insulation with raised drainage and air-circulation channels, and the other side has OSB sheathing. The foam also has a film that is moisture-, mildew- and mould-resistant to protect the foam insulation and OSB from absorbing moisture.

When installing this product, the side with the foam insulation faces down and goes against the concrete. The foam insulates and helps keep the floor warm by providing a continual thermal break across the entire floor surface, so it’s more energy efficient. It also prevents condensation because it keeps the temperature of the concrete floor from coming into contact with the temperature of the basement’s indoor air.

Before products like Amdry Insulated Subfloors were available, contractors needed to build proper basement subfloor systems themselves.

We’d start by putting down one-inch, rigid foam board and then 5/8-inch plywood or OSB screwed through the foam and into the concrete floor using Tapcon screws, which are designed for concrete. Then a low-expansion spray foam would be applied along all the exterior edges, and finally we’d seal all the joints with Tuck Tape.

Think about how long that would take and how much it would cost the homeowner — not to mention that properly putting the whole system together takes the right skill and technique. But now with these new prefabricated panels, not only do we cut down on installation time but also on mistakes.

And it’s not just the subfloor systems in basements we have to think about. Kitchen and bathroom floors should also be watertight.

That’s why we install a waterproof membrane, like Schluter Ditra underlayment, to prevent the tiles from shifting and grout from cracking and to protect the subfloor from water damage. It can also be installed over the Amdry Insulated Subfloor system, so if you wanted to have tile in your basement, there’s a safe way to do it.

Anywhere the potential for moisture is high, you need the right subfloor system to protect your flooring. Because when it comes to your home, it’s the stuff you don’t see that makes the difference between it lasting or not — and that includes what’s below your flooring.

Catch Mike Holmes on Holmes Makes It Right, Tuesdays at 9 p.m. on HGTV. For more information, visit For more information on home renovations, visit

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