Wet underfloor heating installed on a suspended timber floor that doesn't raise the floor level too much

(31 Posts)
audrey01 Wed 28-Aug-13 21:12:40

Does anyone out there have any recent experience of having a wet underfloor heating system installed on a suspended timber floor?

We are currently renovating our house (i.e. everything gutted, sound insulation, external wall insulation, side and loft extension, etc.) and we would like to install underfloor heating in the newly open-plan ground floor space. We would remove all the original floorboards, insulate the void between the joists, lay back the floorboards, lay plywood sheet 18mm, then UFH pipes, then finish with engineered wood. But this would require the whole floor level to be raised by approx. 50mm, which would cause problems with the first step of the staircase, I would imagine.

We have searched the internet for a solution that doesn't involve raising the floor that much and still give us the best heat output. We came across things like "UFH panels placed between the joists", or "wood floor directly on a screed with pipes", but we are not sure if the Celotex insulation between the joists would be strong enough to support the weight of a cement layer.

Has anyone got any direct experience of what solutions might work best? Many thanks!

AwsomeMrsFox Sun 01-Sep-13 21:04:47

We have just laid wet UFH on our suspended floor. We used Myson as our plumber has lots of experience with it. Like you we cellotexted between the joists. Then we laid the diffuser plates between the battens (the coil sits in grooves on the plates, so to this point the floor is the level of the joists. We then put chipboard over it. We are having tiles throughout and out tiler wants us to put another layer of ply just to ensue absolutely no movement to prevent cracking, but I guess with wood you could just go over the chipboard? Then you would only raise the height of the chipboard and the engineered wood. Would that work?

PigletJohn Sun 01-Sep-13 21:18:36

chipboard is an awful material, and best suited for bonfires.

the reason for the ply is to provide extra strength and rigidity. IMO if you had laid 25mm WBP ply instead, it would be a better job and would not have needed overboarding. Tiles need a very solid base as they are not flexible so are liable to crack, which is why your tiler says overboarding is needed.

18mm ply is adequate for a floor that is going to be have carpet or laminate or a wood finish.

audrey01 Mon 02-Sep-13 16:28:59

Thanks AwesomeMrsFox for sharing your experience. Unfortunately, due to our situation of joists running in the same direction as the floorboards, we will need something strong to compensate, so we're definitely going with an 18mm plywood. This will have to sit above the joists, so in order to maximise the heat output we will have UFH installed between the ply and the wood finish, rather than between the joists.

We've been looking at the Nu-Heat product that only has 15mm height (with 10mm pipes) and another product PolyPipe Overlay (which is slightly bigger, 18mm, but comes with 14mm pipes). Given that the difference is not that huge (3mm) and if we are to raise the floor level anyway, would we be better off to choose the bigger pipes 14mm rather than 10mm (thinking that the 10mm pipe might block more easily due to sludge, the 14mm pipe will hold more water so it will have a bigger thermal mass, etc.)

What are people's opinions on this?

audrey01 Mon 02-Sep-13 17:50:30

@PigletJohn - we will probably go for Vaillant, as easier to service in the long time.

AwsomeMrsFox Mon 02-Sep-13 21:30:33

I'm curious PigletJohn what wrong with chipboard? I have to say I never thought about it sludging up audrey01 shock. We went for Myson as their product is Austrian and has been around and very widely installed on the continent for 40 years, but I didn't look too hard into it, so I hope sluding won't be an issue! Why is raising the floor an issue with the stairs? will it make a very short step?

PigletJohn Mon 02-Sep-13 23:49:55

chipboard is weak, and will crack where it is heavily loaded (e.g. under appliance or bed) or frequently loaded (e.g. in front of sink) or impact loaded (e.g. at bottom of stairs or on landing.)

It expands and crumbles if it gets wet

It will not hold a nail or screw.

It is very unlikely that you can lift or move it without irrepairable damage

It is ugly

It is widely used because it is very cheap, and will usually last until the builder has been paid.

A great deal of time is wasted patching it up where it has broken,or cutting it out where it has been damaged by water, especially in bathrooms which often contain some.

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