When transforming a basement into a pleasant, comfortable living area, there’s nothing like a great-looking floor to give the space character. Certain features of basements, however, must be taken into account when choosing and installing a floor finish. Here is some advice to ensure you have a solid, durable base—so to speak—to build on.

Before starting work

Before considering prices and styles of floor coverings available on the market, you’ll need to verify several elements as part of your basement floor finish project:

Step

  1. Carefully inspect the concrete slab for cracks, and repair any that you find.

  2. Check the relative humidity. Does the basement feel humid? Does condensation tend to form on the concrete slab? If so, you’ll need to determine whether it is due to hot, humid air coming into contact with the cooler surface of the slab (a common phenomenon in summer) or moisture being transferred from the ground through the slab.

    To make that determination, measure the rate of relative humidity using a hygrometer and do the following test: cut out a few sheets of transparent polyethylene plastic, about two feet square, lay them at various locations on the slab, and tape down all the edges using duct tape. If, after two or three days, water droplets form on the underside of the plastic sheets, it means moisture is coming up through the slab. This could mean a foundation drainage problem.

  3. Assess the risk of water damage, including the risk of water infiltration—for example, from a leaking window well, or sewer backup if your home has no check valve.

  4. Take into consideration the slope of the concrete slab, which ensures water is properly directed to the floor drains. This is one factor that will help you determine what type of floor finish is suitable for your basement.
    • If the slab is relatively flat, a floor covering can be installed directly over it. A surface with a slight slope can be evened out using self-levelling cement, but this is a costly process and will greatly reduce surface drainage capacity.
    • If the slab has a pronounced slope (i.e., about ¼ in. per foot or more), a subfloor or false floor will need to be built. Once in place, a subfloor will allow for installation of most every type of floor covering.
  5. Check the floor-to-ceiling height: most municipalities require at least 2.1 m (6 ft 11 in) between the finished floor and ceiling. Some authorities tolerate a few obstructions, such as ceiling beams, bulkheads covering ductwork, etc.

Options for building a subfloor

Depending on the ceiling height, the condition of the slab and the humidity level, you may want to choose a raised subfloor or a false floor with a drainage membrane.

Raised subfloor

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

The main steps in building one are the following:

  1. Cover the slab with a vapour barrier material (e.g.: polyethylene).

  2. Install a level wood framing structure that allows water to flow to the drain, and screw standard sheets of exterior-grade 5/8 in. plywood to it.

  3. Add the appropriate underlayment on top of the plywood; the floor finish will go on top of this layer.

For greater comfort and if the ceiling height permits, you can include rigid foam insulation boards in this assembly.

False floor with drainage membrane

You can also opt for a false floor with a drainage membrane. This system is suitable for slabs with very slight slopes and is an interesting avenue if ceiling height is restrictive.

The principle is simple: a membrane made of vapour-barrier plastic material with an underside covered in studs about 1/4 in. square, which create space for air to circulate and water to drain along the slab.

The main steps of installation are as follows:

  1. Unroll lengths of drainage membrane, stud side against the slab, and seal joints with construction tape.
  2. Cover directly with a flexible underlayment before adding the floor covering.
    OR
    Lay plywood (screwed through the drainage membrane into the concrete), followed by the underlayment and floor covering (whether glued or “floating”).

Drainage membrane is also available preglued to 24 in. x 24 in. tongue-and-groove OSB (oriented strand board) panels for “floating” installation; laminate flooring can then be laid over top, but not ceramic tile.

The floor finish

Your choice of floor finish depends on the surface it will be installed on.

Directly on concrete slab

If you are installing directly on the slab, you have a choice of:

  • ceramic tile;
  • laminate flooring on top of a vapour-barrier underlayment; or
  • a flexible covering such as linoleum or vinyl; it is easier and less expensive to install, and among other advantages, maximizes headroom.

On a levelled, waterproofed subfloor

A levelled subfloor can serve as the base for practically any kind of floor finish, each of which has its advantages and disadvantages. For the basement, however, avoid coverings that are vulnerable to humidity, such as hardwood planks and carpeting.

Hardwood No manufacturer’s warranty, because of the greater risk of damage from humidity or water infiltration than on upper floors.
Engineered wood and laminate flooring Higher-quality products are the best choice, as they are more resistant to humidity.
Ceramic tile Offers the best resistance to humidity and will better survive a flood than other products.
Flexible coverings, e.g., linoleum, vinyl Maximizes headroom.

Finally, remember that, beyond all these considerations, the floor covering you choose should be good for your house, for your health and for the planet. To accomplish this hat-trick, choose the greenest types of flooring, which are environmentally friendly and sustainably produced.