Reducing floor thickness with UFH

[nell]

We are doing 2 upstairs bathrooms, the 1st has been completed with 15mm WBF ply on top of the floor boards (screwed at frequent intervals) then a layer of latex self leveling compound with the heating mats embedded and finally the flex adhesive and the tiles.
The only problem is that the floor has been raised by nearly 2 inches.

In order to reduce the increase in the floor height on the 2nd bathroom the Plummer suggested removing the floor boards and fitting 19mm “green” loftboard (with glue and frequent screws), then a waterproof membrane, and then either latex self leveling compound or flex tile adhesive to embed the heating mats.

Most of the posts I can find on the web suggest ply on top of floor boards, no mention of removing the floor boards.

I am concerned that even with the layer of level leveling compound that the floor may still flex and crack the tiles.

Our local tile store says it should be fine.

Any advice would be welcomed.

 

[grumpygrouter]

If you are going to the expense of removing the floorboards, you need to put down at least 22mm WBP ply. This is more stable than chipboard and stronger. You can then put the heat mat onto the ply and then put levelling compound over the top before tiling with flexy adhesive and grout with flexy grout. Not sure the waterproof membrane going down first will put up with the heat from the heatmat but I have no experience of this. What is the purpose of the membrane, just to protect what would have been chipboard from getting wet? If it is for full protection purposes then maybe putting a backerboard down instead of the membrane would be a better way to go.

See what some of the more experienced wetroom guys think when they respond.

 

[nell]

The floorboards have been almost totally removed in order to re-route pipes etc. I think the idea of the membrane was to stop the loft boards from blowing.

I agree that WBF would be better than the loft boards. I'm just concerned that normally you would have 22mm of floor boards with say at least 15mm of ply making 37mm.

I wonder if just 22mm of ply staight onto the joists would be sufficient to prevent the tiles cracking or is that taking a risk?

 

[David - Tradetiler]

I have done plenty by removing floor boards and using 18 mm ply straight on to joists.

Not an official recommendation but never had any comebacks. That way you only end up with the thickness of the tile as additional height.

I guess if you end up with a free standing bath (ball feet) in between joists it could be a problem but for normal foot traffic I have not seen it fail

22 mm ply is not easy to find in my experience

 

[DHTiling]

Also if going down the ply route , you will need to add noggins at 300mm intervals to remove as much flex as possible.....

 

[grumpygrouter]

22mm ply is much more rigid than chipboard. The reason floors are normally overboarded is to add strength to the floor. This is to compensate for any movement that occurs from the joists and to maybe account for the additional load of the tiling. A lot depends on the size of the floor you are looking to tile. Chipboard is not a very stable substance for tiling though it can and is quite often tiled directly onto with out problem as long as appropriate measures are taken, i.e correct adhesives etc.

Which way you go depends on the area of your floor really. if it is a large area, maybe 25mm ply would be the obvious answer, screwed to the joists at 300mm centres. You may need to add noggins between the joists for additional strength as well and screw the boards to this also.

it is the strength of the floor that is the issue. Chipboard is ok for a small area but as you have the floor up already, if it was me, I would go straight for the 22 or 25mm ply and forget the chipboard.

Ideally, and this depends entirely on the choice of floor adhesive, you will need to seal the back face and edges of the board before laying to reduce moisture sensitive movement. For instance if you are using BAL adhesives, you must seal the back and edges with BAL Bond SBR, or for Ardex-flex 7001, seal with Polyurethane Varnish.

You can then lay your 3mm of heating mat with virtually no step at all then.

 

[grumpygrouter]

Also if going down the ply route , you will need to add noggins at 300mm intervals to remove as much flex as possible.....

You must have written that as I was writing my long post.:mad2:

 

[David - Tradetiler]

Always look out for joists that have been butchered by plumbers. Once you have tiled over them you are accepting the floor as good enough to cover over and tile.

It is worth pointing out to you customer if a joists or two has been hacked too badly. I have seen some very bad ones

 

[nell]

Thanks all for the advice

 

[wetdec]

Hi Nell

I would sugest as you have the boards removed you do the following which will keep your height down :

Remove all existing boards.

Insulate between joists

Install an underfloor heating film (not a surface cable)

Overboard with 18/22mm Ply wood

Lay Dura-CI wetroom tanking / uncoupling membrane found HERE

Fix tiles and grout when thoroughly dry.



Tiler

..

 

[DHTiling]

Hi Nell

I would sugest as you have the boards removed you do the following which will keep your height down :

Remove all existing boards.

Insulate between joists

Install an underfloor heating film (not a surface cable)

Overboard with 18/22mm Ply wood

Lay Dura-CI wetroom tanking / uncoupling membrane found HERE

Fix tiles and grout when thoroughly dry.



Tiler


..

Hi tony..

Can't say i have heard of this system.....is it similar to the under laminate one..?

and i thought you have to leave ventilation under timber floors...? when tiling and UFH..

A bit more info on this system might help the member ...cheeeeeeeeers..

 

[wetdec]

A complete electric underfloor heating solution for new build - Suspended Timber Floors.

A Unique Under Floor Heating System that is installed under the floor, between the timber joists to provide either primary heat or supplementary heat in new build projects. To achieve the best results, insulation must be installed below the heating element.

The result is a warm, dry which is maintenance free and has a reduced installation height


Quick Installation


The film element for this type of wooden floor application should have a maximum heating effect of 90W/m . The maximum floor temperature should be controlled by an effective floor temperature sensor to a temperature recommended by the flooring manufacturer, usually 27 C. Particle chipboard flooring is recommended for installation over Ecofilm elements. Care should be taken when Pine T&G boarding flooring is used as some stability problems may occur. An un-coupling membrane should be used when tiling onto any wooden sub floor to prevent cracking caused by latteral movement.

Available in 3 widths; 300, 400 and 600mm to match joist centres. The product is perforated along the 50mm clear edge. This allows the border to be bent to a right angle (90 deg) to allow attachment to the joist when installing, Maintain a 40mm space between the perforation and the top edge of the joist. The element should be attached with staples to the wooden joists.




Hows that ............






..

 

[DHTiling]

I knew you would come up trumps........lol lol...

 

[wetdec]

Thats what I do init.....:yes:


Thanks


..

 

[DHTiling]

Yes i know i was just teasing.....but interesting system......

 

[pjrich]

To comply with the 17th edition IET wiring regulations the heating film would have to covered with an earth shield / grid. Extract Below

753.411.3.2 RCDs with a rated residual operating current not exceeding 30mA shall be used as disconnecting devices. In the case of heating units which are delivered from the manufacturer without exposed-conductive-parts, a suitable conductive covering, for example, a grid with a spacing of not more than 30mm, shall be provided on site as an exposed-conductive-part above the floor heating elements or under the ceiling heating elements, and connected to the protective conductor of the electrical installation.

I have spoken (at length) to the NICEIC about this and have confirmed that if a flooring system is not supplied with an earth shield integeral the to heating, then a seperate earth grid must be installed.

These regulations only came in to force on the 1st July 2008.

I have spoken to a few manufacturers / suppliers of carbon film heating and ,as yet, none have advised me of a solution for providing the necessary earth grid.

If anyone knows of a solution I would be very interested to hear it.

Peter

 

[DHTiling]

Cheers peter...Has the 17th edition altered anything to do with standard mat or loose wire systems..?.... by that i mean fixers are still ok to install as long as no connection is done ....no change to that then......?

My son is a sparky but hasn't looked into that bit yet....

 

[pjrich]

Dave,

The main points of Section 753 - Floor and Ceiling Heating Systems are:-

1) Must be protected by a 30mA RCD
2) Heating must have integeral earth or be covered with earth grid.
3) Max operating temp must be 80deg C, floor surface must not exceed 35deg C.
4) Heating cables, etc must comply with BS 6351
5) Heating cables, etc must be IPX7
6) Specific information of the installation must be left with the end user.

The above is just a summary, the full section is 3 pages. I will try to post more detail later.

Peter

 

[DHTiling]

I know that bathrooms have to go on a sepaerate RCD unit now so how will that effect tilers if just putting UFH in.....?..

Kitchens will not be a problem it's more bathrooms we need to know about pete if you can please......

 

[pjrich]

Just had another conversation with technical at the NICEIC to confirm my thoughts and this is what I've established with regard to bathrooms and electric underfloor heating.

1) If the electrical installation has no existing RCDs then you should either upgrade the consumer unit to 17th edition requirements (likely to cost £400 +) or use fused spur with an integeral RCD to power the underfloor heating (Total power must not exceed 3000W)

2) If the electrical installation has a relatively modern consumer unit with RCD protection on the ring main(s) (Sockets) then it is acceptable to use a normal fused spur off the local circuit.

3) If an completely new circuit has to be installed from a consumer unit then is must be protected by a 30mA RCD.

Hope this helps, if anything is needed let me know and I'll do my best.

Forgot to mention that all UFH systems supplied by www.uheat.co.uk comply fully with the current regulations :yes:

Peter

 

[DHTiling]

Cheers pete..that makes sense really...........

 

[wetdec]

Removed

 

[grumpygrouter]

To comply with the 17th edition IET wiring regulations the heating film would have to covered with an earth shield / grid. Extract Below

753.411.3.2 RCDs with a rated residual operating current not exceeding 30mA shall be used as disconnecting devices. In the case of heating units which are delivered from the manufacturer without exposed-conductive-parts, a suitable conductive covering, for example, a grid with a spacing of not more than 30mm, shall be provided on site as an exposed-conductive-part above the floor heating elements or under the ceiling heating elements, and connected to the protective conductor of the electrical installation.

I have spoken (at length) to the NICEIC about this and have confirmed that if a flooring system is not supplied with an earth shield integeral the to heating, then a seperate earth grid must be installed.

These regulations only came in to force on the 1st July 2008.

I have spoken to a few manufacturers / suppliers of carbon film heating and ,as yet, none have advised me of a solution for providing the necessary earth grid.

If anyone knows of a solution I would be very interested to hear it.

Peter

Does this apply in Scotland as well because I think we have different regs up here?

 

[pjrich]

The 16th edition regs only used to ask for earth screen, etc in the bathrooms / wet rooms etc.

The new 17th edition wiring regulations require earth screens / grids for all electric underfloor heating installations, not just specific rooms.

Using electrical separation is no longer an acceptable method of installation to comply with the current wiring regulations. It was acceptable up to 1st July 2008 when the 17th edition came in to force.

I believe IET wiring regulations cover scotland as well, but I will check and come back to you to confirm.

Peter

 

[Dan]

A complete electric underfloor heating solution for new build - Suspended Timber Floors.

A Unique Under Floor Heating System that is installed under the floor, between the timber joists to provide either primary heat or supplementary heat in new build projects. To achieve the best results, insulation must be installed below the heating element.

The result is a warm, dry which is maintenance free and has a reduced installation height


Quick Installation


The film element for this type of wooden floor application should have a maximum heating effect of 90W/m . The maximum floor temperature should be controlled by an effective floor temperature sensor to a temperature recommended by the flooring manufacturer, usually 27 C. Particle chipboard flooring is recommended for installation over Ecofilm elements. Care should be taken when Pine T&G boarding flooring is used as some stability problems may occur. An un-coupling membrane should be used when tiling onto any wooden sub floor to prevent cracking caused by latteral movement.

Available in 3 widths; 300, 400 and 600mm to match joist centres. The product is perforated along the 50mm clear edge. This allows the border to be bent to a right angle (90 deg) to allow attachment to the joist when installing, Maintain a 40mm space between the perforation and the top edge of the joist. The element should be attached with staples to the wooden joists.




Hows that ............






..

cough cough - that "unique" system is manufactured by a company called Flexel International based in Scotland, and it's actually unique to them.

Uheat may be able to get you that if you want it. Cheaper than Varme sell it.

 

[wetdec]

Yes thats right, Flexel also make an earth shielded cable version for wet rooms, bathrooms etc. Varme do a similar cable system but not the film thats why we changed.

tiler

..

 

[aflemi]

A complete electric underfloor heating solution for new build - Suspended Timber Floors.

A Unique Under Floor Heating System that is installed under the floor, between the timber joists to provide either primary heat or supplementary heat in new build projects. To achieve the best results, insulation must be installed below the heating element.

The result is a warm, dry which is maintenance free and has a reduced installation height


Quick Installation


The film element for this type of wooden floor application should have a maximum heating effect of 90W/m . The maximum floor temperature should be controlled by an effective floor temperature sensor to a temperature recommended by the flooring manufacturer, usually 27 C. Particle chipboard flooring is recommended for installation over Ecofilm elements. Care should be taken when Pine T&G boarding flooring is used as some stability problems may occur. An un-coupling membrane should be used when tiling onto any wooden sub floor to prevent cracking caused by latteral movement.

Available in 3 widths; 300, 400 and 600mm to match joist centres. The product is perforated along the 50mm clear edge. This allows the border to be bent to a right angle (90 deg) to allow attachment to the joist when installing, Maintain a 40mm space between the perforation and the top edge of the joist. The element should be attached with staples to the wooden joists.




Hows that ............






..

I found this very useful post when searching how to fit ufh in my en-suite, hope you don't mind I dredge it up, Wet-Dec and ask for advice?
I have had an extension built with an en-suite. The floor has been suspended up to 450mm (to allow for a sunken bath). I have also had a 'wet-area' dropped down where I will use a former and tanking membrane on the walls. The floor has been suspended on 6x2 joists and consists of 18mm ply (lightly screwed down initially for access).
I intend to install ufh on the rest of the floor but am also slightly concerned that splashing from the bath, wet-area etc could soak through to the ufh. Would the system described above (1) with ufh underneath the ply base give out enough heat ie through the ply and tiles?
I had intended to (2) secure the ply properly, lay insulation board over, then ufh, then tanking membrane. Then adhesive and tiles. Would the membrane be ok laid to close over the ufh?
The thickness of the insulation board adding to the depth is not a big issue although all else being equal, I would prefer the floor lower rather than higher.
In summary I have 2 questions: Under (1) would the ufh give out enough heat through the ply. Under (2) would the membrane be stable laid over the ufh (obviously in a layer of adhesive).
Thanks for help....

 

[Uheat]

I found this very useful post when searching how to fit ufh in my en-suite, hope you don't mind I dredge it up, Wet-Dec and ask for advice?
I have had an extension built with an en-suite. The floor has been suspended up to 450mm (to allow for a sunken bath). I have also had a 'wet-area' dropped down where I will use a former and tanking membrane on the walls. The floor has been suspended on 6x2 joists and consists of 18mm ply (lightly screwed down initially for access).
I intend to install ufh on the rest of the floor but am also slightly concerned that splashing from the bath, wet-area etc could soak through to the ufh. Would the system described above (1) with ufh underneath the ply base give out enough heat ie through the ply and tiles?
I had intended to (2) secure the ply properly, lay insulation board over, then ufh, then tanking membrane. Then adhesive and tiles. Would the membrane be ok laid to close over the ufh?
The thickness of the insulation board adding to the depth is not a big issue although all else being equal, I would prefer the floor lower rather than higher.
In summary I have 2 questions: Under (1) would the ufh give out enough heat through the ply. Under (2) would the membrane be stable laid over the ufh (obviously in a layer of adhesive).
Thanks for help....

Hi ya,

If you are fitting Tiles then your best product to use would be a cable system, either loose cable or Mat. If you are intending on using an insulation board then 160w/m2 should be suffiecient to give primary heating.

you would cover the cable with a thin layer of SLC (Mapei Fibreplan a good one) so the floor construction will be insulation board, cable, SLC, Tanking membrane

Please see Wetdec for the best membrane to use.

Hope this helps

 

[aflemi]

Great Aaron, many thanks. I'll be onto you for the mat when it's time.
Cheers.

 

[Uheat]

No problems. If have any further questions please get intouch