complicated underfloor heating question

[chrisbainbridge]

Sometime in the next 12-24 months we will move back into our own home.  In the new section we have wet underfloor heating.  The floor is level throughout the house.  i have seen increasing numbers of adverts for small bore underfloor heating which can be laid later and only takes 1.5-2.0cm of the height of the room. 

This is very appealing when allied to a ground source heat pump in the garden.

however this would either mean a step between the existing underfloor heating or we have to build it up by 1.5cm.  is there an approved material we can lay on top of the existing flooring to allow the heat through or even act as an extra thermal mass?

Thank you.

[Tod28]

Assuming the new floor is concrete/screed then you can just add a floor levelling compound on top. Do ch3ck if the current underfloor is cement or gypsum based first.

[chrisbainbridge]

Thank you. That was what I needed to hear.

[aidan.f]

Small bore pipes don't play well with Heat Pumps and radiators. For UFH, I suppose OK unless temperature is increased to compensate for lower flow rates

[HTFB]

There are high-conductivity screeds specifically for laying over underfloor heating. Cemfloor was, I think, the brand we looked at, but I don't know what the contractors actually used. And we had the opposite and more usual problem, of trying to fit everything into the minimum possible depth.

If there's inadequate insulation in the build-up then putting more material above the pipes will increase the temperature in the screed and direct more of the heat flow out into the ground, although sadly not far enough for the GSHP to pick it up and bring it back indoors again. But what counts as "adequate" here is a difficult question and I spent significant effort online failing to find the answer. If the ground is dry it probably isn't very much.

[HTFB]

We have overlay underfloor heating in our flat, over a concrete floor, and upstairs in the very-nearly-complete house over wooden joists. In the flat we used two different types of board with preformed slots for the pipes, as we were able to use some left-overs provided by friends. I think they were both 18mm boards; we have engineered wood flooring on top. The polystyrene board with an aluminium foil spreader is distinctly warmer underfoot on a cold morning with the heating off than the fibreboard is, fwiw.

[chrisbainbridge]

The extension underfloor is beutifully laid on top of several centimetres of insulation, etc   The new underfloor on the old floor would be going directly onto a large concrete plinth so not ideal but better than nothing.

ideally we would have demolished the whole house and started again but architect did not think to suggest it!