Constructional hearth advice

Discussion in 'Building Regulations and Planning Permission' started by DiyCarr, 29 Oct 2020.

  1. DiyCarr

    DiyCarr

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    Hi,

    I’m in the process of building an extension with a suspended timber floor. An after thought was the wood burning stove! I now need to retrofit a constructional hearth of 125mm but I’m conscious of the additional weight of this with the stove and the flue above.

    my thinking is to remove the 840x840mm area of chipboard floor and replace with Hardie backer 12mm then add 100mm thermalite blocks before pouring a 25-30mm concrete slab which will then be polished to give a finished hearth to sit the stove on. The addition of the thermalite blocks should save a lot of weight, but I can’t find any info to say whether this is acceptable for building regs?

    any advice or thoughts welcomed!
     
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  3. frutbunn

    frutbunn

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    Are you leaving the joists in place and lying the hardiebacker board on the joists?
     
  4. DiyCarr

    DiyCarr

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    Yes, leave the joists in place.
     
  5. frutbunn

    frutbunn

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    In that case no, there needs to be an air space of 50mm between the hearth and combustible material.
    [​IMG]
    Or your appliance won''t cause the upper surface of the hearth to exceed 100 degrees C
     
  6. BoredSeb

    BoredSeb

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    Two things - a majority of modern wood burning stoves don't require a full constructional hearth as they are designed to have cool undersides. Check manufactures requirements.
    Second - you really don't need to start pouring concrete with modern materials. I used 90mm of Skamotec underneath mine, sealed with SBR and then tiled. There are other fire boards available, Have a look here - https://stovetech.co.uk/product-category/fire-board/

    IMAG4689.jpg IMAG4807.jpg
     
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  8. DiyCarr

    DiyCarr

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    Do the same rules apply if the stove is not in a fire recess (i.e. free standing in the room)?
     
  9. DiyCarr

    DiyCarr

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    Thanks for the info. Are you saying that you can use 90mm of fire board above timber floors as a constructional hearth?
     
  10. BoredSeb

    BoredSeb

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    You probably still need to refer to the manufactures spec, but what I can tell you is that the 50mm Skamotec I have to the side of my stove is too hot to touch on the tiled side and completely cool on the other side!
    I guess if you wanted to follow the letter of the law and allow for an air gap, you could frame with 50mm Skamotec then put a full board over.
    But, in answer to your question, yes, I'd just build over the floor.
     
  11. Laurieo

    Laurieo

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    Depending on what Kw stove your getting I've seen glass hearths that don't need a concrete base .
    There website is stoveworlduk.co.uk .
     
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    DIYnot Local

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