Need help with understanding hearth regulations? Our resident expert Reece Toscani is on hand to help:
I am about to buy a wood-burner and I understand I need a hearth. I have a wooden floor but am bemused by Document J as to what my options are. Can you cast some light on the subject?
Dear ‘Hearth’ Vader
Thanks for getting in touch, this is a tricky subject and Document J is not the clearest when it comes to hearth requirements. As with all advice it should be used in conjunction with the specific stove manufacturer’s installation manual, but as a rough guide there are two main types. Superficial hearths and constructional hearths. If your stove has been tested and generates a hearth temperature of less than 100°C then you can use a superficial hearth. If not then you will need to use a constructional hearth.
A constructional hearth needs to be 250mm thick as it is typically made up of a concrete base under the floor with a decorative material on the surface, you would then place the stove on top of this decorative material. Providing the material is non-combustible there is a lot of choice available in regards to materials, but typically some form of natural stone is commonly used: granite, sandstone or slate.
One thing to keep in mind is that natural stone is prone to cracking if it is laid in a single piece, so often the material will need to be cut to allow for the expansion of the stone due to the heat coming from the stove.
If your stove has been tested and does not produce a hearth temperature greater than 100°C then you can use a superficial hearth. The minimum requirement for this 12mm and can be placed directly on top of a combustible material. For example if you have an extension with wooden floors throughout you could buy a 12mm glass floor plate and place this on top of the wooden floor and put your stove on top of the glass floor plate and that’s it. Again providing the material is non-combustible, it is a minimum of 12mm thick and you allow for the expansion you have a variety of materials available.
There is a third option, which is applicable when you plan to install your stove onto floor that is already non combustible. Both examples above apply, if the stove produces heat greater than 100°C then providing the non-combustible flooring is at least 250mm thick there is no problems.
Alternatively if it is less than 250mm and the stove produces a hearth temperature less than 100°C this will also be fine. In this situation the entire floor is effectively the hearth, however building regulations also state that as well as the combustibility of the material and the thickness used, there should be a visual indication of a hearth.
This serves the purpose of defining the area of the fireplace, letting everyone in the room know that it could be hot in that area. This can be achieved by placing a 1mm thick sheet of steel down underneath the stove so visually you can see the allocated hearth area. Alternatively if you are planning an extension and haven’t laid the hearth yet you could choose a different colour flooring to indicate the hearth of your stove, so there is no trip hazard but a clear visual difference between the floor and the hearth area.
The most important part to take away from this is safety, you are about to put a large metal box filled with fire into your home, so you need to make sure there is adequate heat/fire protection around and above the stove as well as beneath with a hearth. We supply a range of materials that are ideal for hearths, including natural stone, glass, steel, resin or tiles. All materials are available in a wide choice of colours and finishes to match the décor of your room.
Whilst Document J can sometimes get caught up with legal terminology and perhaps vague or contradictory regulations, it is a legal document and worth consulting prior to purchasing. If you are still unsure consult a skilled and qualified stove installer who will be able to provide and onsite survey and advise based on your specific requirement.
Alternatively get in touch with our knowledgeable team who are ready to help.
If you have a question that you would like answered by Reece then please leave a comment below or get in touch via email!