Stove Hearth & Visual Warning Area

[soapstar]

Hey Folks,

 

On to the wood burner now! Question relates to the constructional hearth and what is referred to the Visual Warning Area - from what I gather this is usually the raised area around the stove, usually made of slate etc.

 

We have the constructional hearth in which is 1m x 1m, this was done before the UFH pipes were installed for obvious reasons. However I am concerned this will be quite small to sit a wood burning stove plus all the other utensils etc.

 

Given we have UFH pipes around the 1m x 1m area can the VWA (slate slab) be wider than the construction hearth beneath and partially cover some UFH pipes? 
 

The screed is to be poured on top of the pipes obviously with the wooden shutters to construct the hearth.
 

I have uploaded an image for reference!

 

thanks 

[Thedreamer]

Not sure what the visual warning area is.

 

Our Caithness hearth is 104cms by 80cms. We have dense concrete block sitting on the concrete slab. Is the stove going to be free standing or boxed in?

 

That stove is Charnwood C-4 for reference.

 

[the_r_sole]

I've never heard the term visual warning area before, where has that come from?
(and it's rare to see a full constructional hearth these days too!)

 

The finish of the hearth can be any size, I've done them the full width of rooms before...

[jamieled]

Have a look here, explains it reasonably well:

 

https://www.stovefitterswarehouse.co.uk/pages/hearth-regulations

 

[ProDave]

That is almost certainly too small for a constructional hearth.

 

You will need a stove that guaranteed no more than 100 degrees at the base and does not need a constructional hearth, then you just need a 12mm stone or glass superimposed hearth

[soapstar]

9 minutes ago, Thedreamer said:

Not sure what the visual warning area is.

 

Our Caithness hearth is 104cms by 80cms. We have dense concrete block sitting on the concrete slab. Is the stove going to be free standing or boxed in?

 

That stove is Charnwood C-4 for reference.

 

That’s interesting thanks, your hearth looks nicely proportioned with your stove.

 

Our stove will be free standing.

 

i believe the ‘visual warning area’ is basically what defines the ‘danger area’ around the stove, so in your case it would be the black block. The constructional hearth is the concrete below the floor. From what I can gather if your floor does not have UFH the constructional hearth is basically the entire floor given it will be concrete, however if you have UFH pipes the constructional hearth needs to be dug out as in my picture.

 

[soapstar]

5 minutes ago, ProDave said:

That is almost certainly too small for a constructional hearth.

 

You will need a stove that guaranteed no more than 100 degrees at the base and does not need a constructional hearth, then you just need a 12mm stone or glass superimposed hearth

Thats concerning - what size would you recommend?

 

I was hoping a 1m x 1m constructional hearth would be enough to contain the heat from the stove and we would be ok to have a slate slab wider than this which may overlap the UFH pipes?

[PeterW]

25 minutes ago, soapstar said:

We have the constructional hearth in which is 1m x 1m, this was done before the UFH pipes were installed for obvious reasons. However I am concerned this will be quite small to sit a wood burning stove plus all the other utensils etc.

 

Given we have UFH pipes around the 1m x 1m area can the VWA (slate slab) be wider than the construction hearth beneath and partially cover some UFH pipes? 
 

The screed is to be poured on top of the pipes obviously with the wooden shutters to construct the hearth.

How deep is the screed..?? If the screed plus the hearth are a minimum of 125mm then you will be fine. That could be as simple as 100mm of screed plus 25mm of slate or stone. 
 

To be classed as a constructional hearth it has to be non combustible so your screed counts. 

[PeterW]

4 minutes ago, soapstar said:

From what I can gather if your floor does not have UFH the constructional hearth is basically the entire floor given it will be concrete, however if you have UFH pipes the constructional hearth needs to be dug out as in my picture.

Not sure who has told you that ..? I can’t find any reference. 
 

99% of stoves these days have a temperature of less than 100c on the base so this becomes irrelevant. 

[soapstar]

6 minutes ago, PeterW said:

How deep is the screed..?? If the screed plus the hearth are a minimum of 125mm then you will be fine. That could be as simple as 100mm of screed plus 25mm of slate or stone. 
 

To be classed as a constructional hearth it has to be non combustible so your screed counts. 

I am not 100% on the depth of the screed but 100mm seems about right. This begs the questions what is the point in the constructional hearth if the screed + slate will be sufficient?

Edited September 1, 2020 by soapstar

[ProDave]

Re the visual warning area.

 

In our last house, we had a constructional hearth finished with tiles.  The rest of the room was wooden flooring.  As a design feature I set the tiles of the hearth dead level with the wooden floor.

 

There was much sucking of teeth by the BC inspector as he said it needed to be raised, but he did pass it as he could not point to anything specific that saud it had to be raised, and it was of a different material and so visually different.

[Temp]

Approved Document Part J has the dimensions/rules but they are confusing until you realise that they are different for appliances that can and can't heat the hearth to over 100C, and decide which you are building for.

 

If it can (eg open fire basket) you need diagrams 24-26 on pages 37 and 38.

 

If it can't (eg stove on legs) you can use diagram 26 and 27 on pages 38 and 39. 

 

https://www.planningportal.co.uk/info/200135/approved_documents/72/part_j_-_combustion_appliances_and_fuel_storage_systems

 

 

 

[joe90]

https://www.stovesonline.co.uk/stove-hearth-size.html    Any good? I bought my stove from them and they were very helpful.

[Temp]

43 minutes ago, ProDave said:

Re the visual warning area.

 

In our last house, we had a constructional hearth finished with tiles.  The rest of the room was wooden flooring.  As a design feature I set the tiles of the hearth dead level with the wooden floor.

 

There was much sucking of teeth by the BC inspector as he said it needed to be raised, but he did pass it as he could not point to anything specific that saud it had to be raised, and it was of a different material and so visually different.

 

My understanding is that the raised area (I've not heard it called the visual warning area either) is raised to discourage rugs from being placed too close. 

 

 

[Thedreamer]

1 hour ago, soapstar said:

I am not 100% on the depth of the screed but 100mm seems about right. This begs the questions what is the point in the constructional hearth if the screed + slate will be sufficient?

 

As mentioned previously constructional hearths are less common. In the past more ground floors would have had joists and the constructional hearth would have provided fire protection. Our floor which has joists the hearth is the only place that has a concrete slab this was also needed to support the weight of the dense concrete blocks around the stove.

[soapstar]

Thanks everyone for the helpful information and links.

 

It would seem this constructional hearth isn’t really required given many stoves seems to reach a temperature less than 100c.

 

so I guess my main question now is can the slate or whatever material we choose to sit the stove on go over the UFH pipes below? For example is we have a slate slab which is say 2m in length. Our constructional hearth as in photo is 1m wide meaning 500mm overlap either side which would be overlapping the pipes somewhat. Would this be ok?

[ProDave]

I don;t see any problems with the stone hearth overlapping the UFH pipes.

[PeterW]

No issues with pipes under the hearth as unusual for anyone to drill into the floor under a stove. 
 

[soapstar]

Thanks ? I guess the only real negative is the small portion of UFH pipe the slab would cover wouldn’t be as efficient as the rest of the room but it would be extremely minimal I assume!

[PeterW]

@soapstarwhat will your final floor covering be over the UFH ..?

[soapstar]

31 minutes ago, PeterW said:

@soapstarwhat will your final floor covering be over the UFH ..?

On top of the screed it will be carpet ideally 

[PeterW]

Ok so your hearth will actually be more efficient not less because the slate will conduct heat better than carpet and underlay. Don’t forget for UFH areas you can get low TOG underlay. 

[Temp]

I was going to use slate but was told it scratches easily. Went for some black granite found at a local stone masons yard that I think was left over kitchen worktop. Got him to hone off the glossy surface to give a silk finish. 

[joe90]

I have installed slate hearths for people even tho I advised against it because they scratch easily, guess what, they wished they had not!!!

[ProDave]

We have a slate tiled floor that wears very well, we chose slate because it wore so well in our last house.  So if slate is okay for a floor, why would it not be for a hearth?