How thick must a log burner hearth be?

A log burner needs a hearth either 125mm thick or as thin as 12mm, and your stove decides which. In England, Approved Document J sets both figures. This page shows how to tell which one you need.

Why are there two thicknesses?

Approved Document J gives two routes. A stove standing in the open sits on a constructional hearth at least 840mm square and 125mm thick. A stove tested to keep its hearth under 100°C can stand on a 12mm hearth instead.

When is 12mm enough?

Only when your stove is tested to keep the hearth under 100°C, and its manual will say so. If it does not, 12mm is not an option.

A 12mm hearth must also reach 225mm in front of the stove and 150mm out from each side. For an open fire, or a stove used with its doors open, the front figure is 300mm.

When do you need 125mm?

For any stove without that test. That means a constructional hearth, at least 840 × 840mm and 125mm thick. A concrete hearth can sit on top of it as the finished surface.

What if the manual asks for more?

The manual can ask for more than the regulations do, and then the manual wins. Your installer signs off the result. Send us the stove model, and we draw the hearth to the rules and the manual before anything is cast.

Do the same rules apply in Wales and Scotland?

No. Wales and Scotland have their own rules. The figures on this page are for England.

Can concrete take the heat?

Approved Document J names concrete as a hearth material. On a ROKA hearth, the working limit is the sealer, rated to 149°C. A stove allowed on a 12mm hearth keeps the surface under 100°C, well inside that.

Where do you go from here?

Sizes, prices and the shop are on our concrete hearths page. Or order free samples to see the colours in your hand.