Restricted height flooring problem

[vetinry]

Hello everyone

This is my first post here although I've been browsing for the last few days.

I apologise if this specific question has been asked before but if so, I haven't found it.

We bought a house back in February and I'm mid way through first of many refurbishment projects.

This has involved knocking down a wall between Kitchen and Dining room to make one large room.

The floor is simply polished floorboards over battens and they're not particularly well secured.

I'd like to add underfloor heating but:

a. I'm a bit restricted by floor height (currently 85mm to top of floorboards) which is the same throughout the downstairs of the property
b. The house was built in 1987 so I'm guessing there isn't much in the way of insulation in the concrete slab.

So, what I'm thinking to try and keep height to a minimum is

55mm battens at approx 300mm centres.
40mm Kingspan K3
15mm water pipes clipped to insulation
Dry screed mix (or kiln dried sand) to surround pipes to top of battens

This is where the potential problems start.

Since height is a concern, I have thought about using 12mm tiles and allowing 3-5mm for adhesive.

So, by using 18mm plywood, this will bring the overall floor height in at 3-5 mm over rest of house (I can certainly live with this)

I guess the questions are:

1. Is 18mm ply is sufficient to avoid movement - I can screw it down along the battens as closely spaced as necessary.
2. Will glueing the battons to the floor help reduce any movement in the floor?
3. Are there any other options to give a stable base but without too much additional height (insulation plus screed is going to be much higher) since I have already cut insulation down to an absolute minimum
4. How much will 18mm ply restrict heat to the tiles?
5. Will a very good quality flexible adhesive help?

Thanks in advance for all advice

I've just popped a request for an experienced floor tiler in the relevant section. I live in South Oxfordshire, just off the A34

Best wishes

Steve

[Ajax123]

There are quite a few systems nowadays for restricted height scenarios in refurbs. One have been involved with and is an extremely effective system is called the Max4 ILM system. The benefit is that it is a screeded system which offers thermal mass but is a very thin section which allows either reduced floor height or extra insulation. It is a doddle to install as well.

[Ajax123]

Oh by the way, not quite clear from your post but if it is a concrete substrate I would not bother with battens but would go for a floating screeded system. 85mm is quite a reasonable zone.

If you were to reduce the pipe size from 15mm to 10mm you could reduce the screed depth to 35mm. I have just drawn up a spec for someone for this arrangement using 50mm Polyurethane insulation, 10mm UFH pips and 35mm anhydrite screed. Gives great response thermally as well.

[vetinry]

Thanks very much for your reply. My preference would definitely be screed but I didn't think I would be able to use anything less than 50mm anhydrate or 65mm sand and cement, and this was going to take floor height to over 100mm without the thickness of the tile.

Using a "U" value calculator, it seems I can just about meet regs by using 40mm of good quality insulation (am thinking Kingspan K3 or TF70 unless you have a better suggestion) - would that, 10mm pipes and a 35mm screed be strong enough to tile onto?
Do you have the specs of the screed, a price, and a contractor local to me that would pour it

Many thanks

Steve

[Ajax123]

Thanks very much for your reply. My preference would definitely be screed but I didn't think I would be able to use anything less than 50mm anhydrate or 65mm sand and cement, and this was going to take floor height to over 100mm without the thickness of the tile.

Using a "U" value calculator, it seems I can just about meet regs by using 40mm of good quality insulation (am thinking Kingspan K3 or TF70 unless you have a better suggestion) - would that, 10mm pipes and a 35mm screed be strong enough to tile onto?
Do you have the specs of the screed, a price, and a contractor local to me that would pour it

Many thanks



Steve

Yes 35mm on 10mm pipes would be perfectly ok to tile on to. You could go even thinner with some systems like the Max 4 thing.