Underfloor without floor insulation

whiskywhisky

Hi

Not sure if this thread should be here or in the DIY section?

We are starting on a double storey rear extension to our house. We have been planning this for a while and have sourced the builders/plumbers etc. Throughout our planning was that we will have a wet underfloor heating on the ground floor and radiators on the 1 st. The whole heating plumbing system/boiler is being replaced as old is ancient. The ground floor is solid concrete and first is traditional joist and house was built in 1950.

However we have been informed by the builder that it will be a lot cheaper for us to stick to radiators on the existing (old part) ground floor and put in wet underfloor heating in only the new extension on the ground floor. He mentioned that the new part will be built with adequate insulation etc to get best use of the heating. He said if we still went with the underfloor heating on the existing old part, we will be wasting energy and money to heat downwards as well.

Liaising with underfloor companies, mainly dealing with their salesmen they are saying their customer install on existing (without floor insulation) and their systems are amazing etc.

A bit confused, builder is saying to get the best out of the underfloor he will need to dig down a fair amount of the concrete and then lay insulation etc. Which is very costly, the need to dig down is only to lay insulation etc as there is plenty of head height in the room.

Please can someone advise?

thozza

Probably better in the DIY section, however what the builder is saying is correct, without insulation underneath the pipes, you will be heating the ground, which could prove very expensive.

Many UFH companies supply 'low build' or 'overlay' type systems which are designed for retrofit situations, some have high grade thin insulation underneath as well as foil to direct heat upwards. They also have the pipe close to the finished surface of the floor to ensure that heat is directed into the room, it is probably this type that your suppliers have been advising. Installing a standard screed system without any insulation would be a non-starter.

The trade association for UFH heating is BEAMA underfloor, their website which has some useful detail including links to the regulations is here:

http://www.beama.org.uk/heating-water-air-movement/underfloor-heating.html

Many UFH suppliers are members, but not all.

whiskywhisky

Thanks, I was not aware there is the "standard screen" and a specialised with built in insulation. Makes sense now.

matelodave

I installed a PolyPipe overlay wet underfloor heating system in a 140m2 very exposed detached bungalow six winters ago. It's fed by an air source heat pump which heats the whole building and provides all our hot water.

It's laid over a suspended wooden floor - 18mm chipboard panels around 2' above a ventilated space. I tried to do some calculations to decide the cost effectiveness & time penalties of pulling the whole floor up, insulating underneath it and replacing it all. I reckon it would have added around £2k to the job.

Just to lay 12mm Kingspan/Celotex on top of the floor and under the overlay boards would have been around £500. So in the end I decided not to bother.

We average around 7000kwh a year for out total energy costs - heating, lighting, hot water, cooking etc. etc. of which I estimate about half is used for heating = £420 per annum. Last year we only used a total of 6000 Kwh so would have spent even less on heating.

I'm not sure what the loss through the floor would be but even 20% would mean that only £90 a year gets wasted. Just laying Kingspan would take five years to pay back if it eliminated all loss. Doing it properly would be around 22 years.

Actually the savings would be less as you can't totally eliminate all heat loss - the first 10mm will save the most, the next 10mm will save half that and the next 10mm will save even less as you achieve diminishing returns - ie spend twice as much to save half as much

So it might be costing me around £90 a year (but it's probably less) but it saved no end of hassle.

I'd agree that laying an overlay system on a solid concrete screed would probably increase the heat loss but I'm sure that you could make a significant improvement by laying high density Kingspan or similar down under an overlay system without incurring excessive costs or disruption.

Try doing a few heat loss calculations and working out the costs. IMO spending £1000's to save a £100 a year or less is not cost effective .