Basement floor finishes: your options

Assessing the condition of your concrete slab and basement

Before delving into the myriad options for floor coverings, you need to assess your existing basement floor.

• First, carefully inspect the concrete slab for cracks and repair any that you find.
• Does the basement feel humid? Is there condensation on the concrete slab? You need to determine whether it’s a result of warm, humid air coming into contact with the cooler slab, or if moisture from the ground is leeching up through the slab.

  To do so, measure the relative humidity with a hygrometer and perform the following test: Cut out a few 61cm x 61cm (2ft. x 2ft.) squares of transparent polyethylene, place them on different areas of the slab, and seal their edges with duct tape. If water droplets have formed on the underside of the plastic sheets after a few days, it means moisture is rising through the slab. That could mean your foundation has a drainage problem. CAA-Quebec’s Residential Advisory Services can provide advice and answer any questions you may have.

• Assess water damage risks, including infiltration through window wells or sewer backup if your home doesn’t have a check valve.
• Examine the slope of the concrete slab to ensure water flows properly to the in-floor drains. This will help you determine what sort of floor to install.
• Floor coverings can be installed directly on relatively flat slabs. The surface can be levelled with self-levelling cement, but the process is costly and significantly reduces surface draining capacity.
• If the slab has a steep slope of about 6.4mm (1/4in. per foot) or more, you’ll need to install a subfloor. Once the subfloor is in place, you can install the floor covering of your choice.
• Check the ceiling height: most municipalities require at least 2.1m (6.8ft.) from the finished floor to the ceiling. Some jurisdictions tolerate limited obstructions such as beams and bulkheads that cover ductwork.

Subfloor options

Depending on the ceiling height, condition of the concrete slab, and humidity level, you can install a raised subfloor or a floating floor on a drainage membrane.

Building a raised subfloor

A raised subfloor is a good way to level the slab, cut humidity, and create a space for ventilation and drainage under the floor.

Of course, you can hire a general contractor or flooring specialist or do the work yourself. Either way, check your coverage with your insurer before the work starts, as you should for any renovation. Here’s how to build a raised subfloor:

1. Cover the slab with a vapour barrier (e.g., tar paper, polyethylene, or a drainage membrane).
2. Install a level wooden frame that allows water to flow to the in-floor drain(s) and screw standard exterior-grade 16mm (5/8in.) plywood on top of it.
3. Install the appropriate underlayment and floor covering.

If you have enough floor-to-ceiling clearance, you can also add rigid insulation for increased comfort.

Building a floating floor on a drainage membrane

A floating floor on a drainage membrane is another option. It’s suitable for slabs with slight slopes and is a good choice if ceiling height is an issue.

The principle is simple: The membrane is a plastic vapour barrier covered with 6.4mm (1/4in.) dimples. The dimples provide space for air to circulate and water to drain along the slab.

Here’s how to install a floating floor on a drainage membrane:

1. Unroll sheets of drainage membrane, dimple side down, and seal joints with construction tape.
2. Cover the drainage membrane with flexible underlay and install a floating floor on top. You could also screw plywood onto the slab through the drainage membrane and then install the underlayment and fixed or floating flooring.

Drainage membrane is also available pre-glued to 61cm x 61cm (24in. x 24in.) tongue-and-groove OSB (oriented strand board) panels for floating installation. These panels should not be used as a substrate for ceramic tiles.

Floor coverings for basements

The floor covering you choose will depend on the surface on which you are installing it. Here are your options if you decide to install the floor covering directly on top of the concrete slab:

• Ceramic tile
• Laminate flooring over a vapour-barrier underlayment
• A flexible covering such as linoleum or vinyl (a fast and cheap option that maximizes floor-to-ceiling height)

Virtually any type of floor covering can be installed on a levelled subfloor, and each one has its pros and cons. It’s best to avoid flooring that is vulnerable to moisture like hardwood or carpet.

Above all, your choice of floor covering should be good for your house, your health, and the planet. The floor coverings that score well in all three categories are ecofriendly and produced sustainably.

Whatever option you choose, know that investing in renovating your basement will pay dividends when it comes time to sell your home.