Understanding the anatomy of floors - what are the layers of floors?

How are floors made up?

It can be a confusing thing to understand, especially because different tradesmen are responsible for different parts of it. Your builder might talk about the joists and the basement slab, but your carpet supplier will discuss the underlay, and your tiler will talk about waterproofing.

So before you start choosing your flooring it’s best to understand the anatomy of flooring so you anticipate the questions you will no doubt get asked.

Jargon alert! There is a lot of ‘building terms’ in this article but hopefully the diagrams will help you to understand. Don’t forget to check my Renovating Glossary if your stuck.

The layer of floor you normally see is just the decorative floor covering such as tile, laminate, carpet or floorboards. While the actual floor structure is hidden underneath.

Let’s work from the top down.


The floor covering sits on an underlayment. The underlayment is often a foam or cork product which creates an acoustic barrier and makes the floor soft to walk on.


If you remove your floor covering you will find your subfloor. The subfloor is often made from a composite panel or plywood and it spans supportive floor joists. This subfloor layer is likely to be either large sheets or planks. The subfloor provides protection of the joists and acts as a strong base for the floor covering.


understanding floor anatomy2.jpg

The joists sits atop the foundation and are the frame that supports the subfloor. They are often supported at the midpoint by a beam or girder. Joists are sometimes tied together using bridging to create more stability. The bridging can be made from wood or metal.

That’s it! Not too hard right?!

However there are a few other scenarios I might warn you about.

Concrete floors

When the house is built on a concrete slab the scenario is slightly different. The subfloor is fixed on top of timber 2x4 studs. These studs are fixed to the concrete slab but with a layer of plastic sheet in between them and the slab.


When tiling a bathroom you will need an adhesive layer and it is ideal to use a cement based underlayment as the subfloor. You may also want to consider heating cable for underfloor heating. 


So hopefully that makes it easier to talk to your builder :)

Sally xx