What base for tiled hearth over suspended floor?

bazmdiy · 18 Jul 2012

Hi all - please can anybody give advice on what is normally used as a base when creating a quarry tile hearth for a woodburner?

Plywood, floorboards, steel plate?

I'm ok with laying the tiles - its just the type of base.

The joists span 2 metres and are 9". The quarry tiles are 6"x6" and 1" thick. They will be flush with finished floor.

What would a builder normally choose?

Any ideas welcome!

marklamond · 18 Jul 2012

Is this a new install?

Do you have any pics?

In most cases it will have to be something non combustible, a concrete slab formed in situ is often the only choice with a suspended floor. It needs to meet with the regulations, be strong enough to support the stove and take the heat.

Regs won't allow you to finish a hearth flush with the floor covering, it must be raised above the floor level.

1" tiles would be acceptable on a combustible backing if your stove has a "low hearth temperature" but that depends on the stove. Most stoves aren't in this category.

Remember whatever you do needs to comply with building regs.

This will give you a rough idea of what you need to build:
http://www.stovesonline.co.uk/stove-hearth-size.html
(look at the hearth thickness section)

Karis · 19 Jul 2012

bazmdiy said:
What would a builder normally choose?

Methods & materials that comply with the Building Regulations; take note of marklamonds advice, it covers it well. You should also research the Forum archive, stove installation is well covered; //search.diynot.com/forum_sear...tbytime=0&author=&search=Search+Forum&stype=0

bazmdiy · 19 Jul 2012

Marklamond and Karis thank you for your advice. I hope the bit about the hearth not being flush with the floorboards can be overcome - my wife is dead keen on them being flush.
I'm building a new extension on a listed building. The joists are 225mm and the gap underneath them to the oversite concrete (Which is only a 2" screed) is about 500mm. The remains of a bread oven are under the proposed hearth and I'm not allowed to cover it.
The stove (Clearview Vision 500) is freestanding and about 125mm from a brick wall. It sits on an integral steel log stand of 300mm. The hearth area we planned to be 1100 wide by 1000 deep. The distance from the front of the stove to the floorboards is 550mm. I planned 1" thick quarry tiles on a bed of mortar on a 10mm steel sheet (in strips say 200mm wide). But I have never done anything like this before - thats why I'm anxious to get some proper advice.
Incidently one stove HETAS registered installer said floorboards flush with hearth was ok.
I will look for discussions about stove installation as Karis has suggested. I really don't want to contact Building Control - it seems to cause more delay.

Karis · 19 Jul 2012

bazmdiy said:
I really don't want to contact Building Control - it seems to cause more delay.

Unless you use a HETAS installer (preferably one that will comply with the regulations) the fire will have to be inspected & wintess tested by Building Control, they surely must be involved anyway if this is a new extension to a listed building? Your BI won’t sign off the completion certificate if you don’t comply with the necessary Building Regs. & in the worst case, could slap you with an enforcement notice. You also run the risk of invalidating your house insurance on any related claim if the installation is non compliant.

Your wife’s wishes are irrelevant, tell her not to interfere in things she knows nothing about.

bazmdiy · 19 Jul 2012

The installation will be done by a HETAS registered installer. However, I'm finding inconsistencies in their opinions on several matters and I want to be sure about the hearth.

I phoned HETAS who gave me the number of a technical guy from an official organisation (sorry but I've forgot what that was - but it sounded like an approved thing).

He said the recent regs changes were more relaxed and particularly if the stove did not produce 100C at its feet. He pointed me to Building regs part J.
This says the hearth can be as thin as 12mm (not constructional). The area around the stove has to be 300mm fron and 150mm sides. Mine would be 550 and 300 respectively. The perimeter of the hearth has to be "well defined" eg raised above floorboards. However, this is an exaple way of doing it - doesn't read that a raised hearth is madatory.

My wife eats rottweilers for breakfast - she wants flush hearth!

bazmdiy · 19 Jul 2012

Furthermore!

http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADJ_2002.pdf

Building regs part J2. Para 2.26
....
The edges of this (non-combustable surface) should be marked to provide a warning to the building occupants and to discourage combustible floor finishes such as carpet from being laid too close to the appliance. A way of achieving this would be to provide a change of level.

Quarry tiles meeting floorboards is a pretty good demarcation.

Sorted!

Karis · 19 Jul 2012

bazmdiy said:
He said the recent regs changes were more relaxed and particularly if the stove did not produce 100C at its feet. He pointed me to Building regs part J.

Furthermore!
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADJ_2002.pdf
Building regs part J2. Para 2.26 Sorted!

The most recent changes to Part J were in 2010 &, yes, if the stove is raised above the hearth then you can relax the hearth requirements if the temp does not exceed 100 degrees. I was going to check & take a look for you but you seem to be more than up to it yourself. But I would suggest you use the current document as a reference http://www.planningportal.gov.uk/uploads/br/AD_J_wm.pdf the one you link is 10 years out of date! Look in particular at the requirements for solid fuel appliances – starts on page 31.

bazmdiy said:
My wife eats rottweilers for breakfast - she wants flush hearth!

She sounds like an absolute gem, good luck with that one; I prefer dippy boiled eggs myself!

bazmdiy · 19 Jul 2012

Thanks fo that - I've got the latest and it at least confirms the flush hearth.

Now all I need is some advice on what base to lay the tiles on. I think 10mm steel sheet is over the top. Having sorted the stove hearth regs out I may re-post the question around a situation where tiles are just laid on a suspended floor. eg in a kitchen.

Karis · 19 Jul 2012

No need to re-post. Don't lay them on steel plate, the thermal expansion/contraction will most likely be too much for the adhesive & you risk failure. You will still need a firm non combustible tile base, have you considered casting a fully supported screed between joists with a 12.5mm cement tile backer board overlay.

Use a high quality flexible cement powder adhesive but I would avoid using conventional grout as it tends to crack with the heat, I lay the tiles close (1/2mm) & use silicone. Read the tiling forum archive posts for some background.

bazmdiy · 20 Jul 2012

Karis - thank you for info - will follow that advice.

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What base for tiled hearth over suspended floor?

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