Can a concrete hearth go on a wooden floor? What the rules say about the timber underneath

Yes, a hearth can sit on a wooden floor. What the rules check is the timber under it. In England, Approved Document J sets two routes, and they treat that timber differently.

The thick route is a constructional hearth. It is solid non-combustible material, such as concrete, at least 125mm thick. Timber must not sit directly beneath it. You need an air space of at least 50mm between the underside of the hearth and the timber. Or the timber must sit at least 250mm below the top of the hearth.

On a joisted floor, that is a job for your builder. It comes first. A hearth cannot fix it.

The thin route is a board, sheet or tile of non-combustible material, at least 12mm thick. It only applies if the stove is not in a recess. The stove must also be tested to show the hearth surface cannot pass 100°C. That hearth must reach 225mm in front of the stove and 150mm each side. The 50mm and 250mm rule is written for the thick route only.

Your stove's manual says which route it qualifies for. It can ask for more. Then the manual wins.

We cast hearths to the size your stove and the rules give you. The seal on them is rated to 149°C, which sits well above the hearth test limit of 100°C. We do not tell you your joists are fine. Your installer reads the floor and signs the hearth off.

These are the rules for England. Standard sizes, made-to-size hearths and fitting within about 50 miles of Small Dole are all on our concrete hearths page. Free samples show the colour next to your fire.