Underfloor heating advice

[George Hartshorn]

I'm undergoing a renovation project and looking at installing some underfloor heating.

It is a lower ground floor flat with a concrete slab for a floor. It's approx 50sqm and consists of a open plan kitchen/living room and a large bedroom.

The current central heating system pipes are copper and set into the concrete slab. They were installed in the late 80s so i'm terrified that at some point they will leak and i'll have to take up the flooring i'm about to install, and then dig up the slab to fix it which would be costly and intrusive.

As a work around I have been looking at installing UFH on top of the slab and underneath an engineered hard wood floor. This way I could completely remove the old radiators and heating system, eliminating the possibility of it failing. I am also looking at putting a membrane between the slab and the UFH due to damp issues in the flat.

Does anyone know if this system will be powerful enough to heat the entire flat without the need for radiators?

Will there be any issues installing the UFH on top of the Oldroyd membrane?

Is there anything else I should be considering here?

 

[cross thread]

Plenty of companies who supply underfloor will also design it for you, including heat calculation etc ,even for supply only

 

[MeldrewsMate]

If you're willing to go to the expense of ripping up the old slab then consider the Gov't Green Homes scheme, Gov will pay up to 2/3 of cost of installing underfloor insulation, though you will have to use a registered business, and that may be more expensive than paying for it yourself!

Otherwise there are low profile (20mm thick) systems that go over the slab and are quite effective.

 

[George Hartshorn]

If you're willing to go to the expense of ripping up the old slab then consider the Gov't Green Homes scheme, Gov will pay up to 2/3 of cost of installing underfloor insulation, though you will have to use a registered business, and that may be more expensive than paying for it yourself!

Has anyone actually managed to use the scheme?

I've looked into it a few times and contacted a number of companies who are registered but none of them are based in London and none of them have got back to me.

When reading into it, it seems that there has been a really low uptake on businesses registering because of the financial commitment and the time frame that the work has to be carried out (March '21 I think)

 

[Madrab]

Do you know if the damp is permeating up through the slab? It would be unusual for there not to be at least a DPC under the slab, if no insulation as well unless it was really old.

If the slab is dry then it can be channel cut and UFH retrospectively fitted without raising the floor level.

 

[George Hartshorn]

Do you know if the damp is permeating up through the slab? It would be unusual for there not to be at least a DPC under the slab, if no insulation as well unless it was really old.

If the slab is dry then it can be channel cut and UFH retrospectively fitted without raising the floor level.

The slab is presumed to have been laid in 1987 when the flat was last renovated - no idea what building practices were like then - I wasn't even born!

I'm hoping to get into the property tomorrow to check if the slab is damp (haven't completed on the mortgage just yet).

If I were to channel cut into the slab for the UFH, how deep would I go? If there isn't insulation underneath do I risk just spending all my money heating up the ground below?

 

[Madrab]

Check to see if the slab is dry, if so then it will probably have a DPC/DPM.

Heat will always rise .... with milling the slab, the pipework is laid right at the top in a shallow channel therefore most of the heat is at the top of the slab and more heat will rise up into the floor covering than would travel down. There will, of course, be heat loss into the slab below and as with many retrofitted systems it isn't perfect but looking at the information available, heat loss below is a lot less than assumed, especially given the temp that it runs at.

Another point about insulation is that with older houses there is probably a lot more heat loss through badly insulated walls/windows/doors than there ever would be through a concrete slab.