What is a Subfloor?

“Your floor is only as good as your subfloor.”

The Subfloor

What is a subfloor and why is a subfloor important? A subfloor is but one piece of the whole flooring system, which is made up of:

• Joists

• Subflooring

• Finished Flooring

The subfloor rests over the joists of the house, above which the finished flooring will be laid. All of this helps to support the weight of the building. A properly prepared subfloor is essential to the longevity and performance of your flooring solution. If the subfloor is damaged or structurally unsound, problems like moisture damage, uneven floorboards, and squeaky floors will plague your flooring system. Other things like separation of the boards, excessive wear on higher spots, and damage can also occur to the floorboards over a faulty subfloor.

Common subfloors are plywood and concrete. In some old houses, wooden floorboards will be the subfloor, which can be refinished or have new flooring laid over. You will have different underlay requirements depending on the material of the subfloor.

Underlay is an additional layer of material laid over the subfloor, typically used for when you are going to float a click floor over the subfloor. It helps even out the surface, reduce noise underfoot, and increases comfort.

For a concrete subfloor, you would need an underlay with a damp-proof layer to prevent any moisture from seeping into the floor from below, this is because concrete will allow moisture to come through it, and thus cause problems for the visible flooring above.

For wood subfloors, most other standard underlays on the market will do, and you can still use the underlays with damp proof membranes as well.

In some cases underlay will not be required if you are having a new floor installed over a subfloor. The reason for this is some types of flooring like many new LVT floors on the market will come with built-in underlay when you buy it. Or if you choose to use adhesive and stick the floor straight to the subfloor, then you would not need underlay. This is a common solution for tongue-and-groove floors or stick-down vinyl floors.