Ask Reece: Where on ‘hearth’ do I begin?

Need help with understanding hearth regulations? Our resident expert Reece Toscani is on hand to help:

Dear Reece

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?


‘Hearth’ Vader

reece toscani hearth

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.

document j hearth regulations

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.

document j hearth regulations

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.

glass hearth on wooden floor

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!

8 thoughts on “Ask Reece: Where on ‘hearth’ do I begin?

  1. Hello Reece

    Can you offer up some advice/help regarding the necessary requirements for a hearth for a suspended wood burning fire? The fire itself is suspended over a wooden floor and don’t really want to spoil the look/effect by installing a brick/slate/stone hearth. Is the option of a flexible, removable silicone(as used in food grade type kitchen utensils/cookware) circular mat be suitable? They are certified up to 250 degrees C and offer more convenient, cost saving alternate. Plus the benefits of removing them when not in use.

    Any thoughts/advice would be greatly appreciated.

    Many thanks


    1. Hi Simon, its a good question. Ive not heard of silicone being used as a hearth before. That being said the stipulations would state non-combustible so i guess if it meets that criteria then you should be okay. The only issue i can forsee is that if it can be removed im not sure how well that will sit with the installer signing off the installation, so probably best to speak to them i would say. We love suspended stoves so hope it all goes well and feel free to tag us in any images you post online.


  2. Hi, we are have an extension built and are planning on having a freestanding log burner. I understand I don’t need a hearth as the flooring will be tile but then I have been told that I need to have something in place for visualy impaired people to assist them in noticing where the log burner may be. Can you help please?

    1. Hi Claire,

      Yes this falls under the visual demarcation of the hearth area as per building regs. So, what we have often found when its a new build and you plan to place a woodburner on top of a tiled floor, is to use a different colour tile under the log burner as the visual demarcation to satisfy building regs. That can you keep the flush floor look and satisfy BR at the same time. Hope it helps, Reece

  3. Hi,

    If the stove is to be installed in a recess and it produces less than 100 degrees in downward heat, is a constructional hearth required?


  4. Hi,

    If the stove is to be fitted in a recess and it produces less than 100 degrees in downward heat, is a constructional hearth required?

    1. Hi Matt, best checking with the manufacture’s guidelines as I suspect the fact that it is going into a recess would affect the heat retained. That being said if it’s a traditional brick fireplace, you will likely have a constructional hearth in place acting as a foundation for the chimney to be built upon? Might be worth double-checking what you already have, and confirming with the manufacture about superficial hearths in chambers.

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