Constructional hearth advice

[DiyCarr]

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!

 

[frutbunn]

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

 

[DiyCarr]

Yes, leave the joists in place.

 

[frutbunn]

Yes, leave the joists in place.

In that case no, there needs to be an air space of 50mm between the hearth and combustible material.

Or your appliance won''t cause the upper surface of the hearth to exceed 100 degrees C

 

[BoredSeb]

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/

 

[DiyCarr]

In that case no, there needs to be an air space of 50mm between the hearth and combustible material.

Or your appliance won''t cause the upper surface of the hearth to exceed 100 degrees C

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

 

[DiyCarr]

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/

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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?

 

[BoredSeb]

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.

 

[Laurieo]

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 .