Underfloor heating dilemma

[mikethepipe]

I've been asked to quote for heating an office space-new build-it should be having underfloor heating-but there is only room for 75 mm absolute max screed,as is common practice,the insulation is under the slab.The buider has been told that this is ok as the slab willbecome part of the thermal mass.The systems I have been involved with in the past are the john guest speedfit and hep2o.When I checked with speedfit,they were very clear thet a thin ( v.expensive) insulation layer must be incorporated between the ufh pipes and the slab.As the cost of this insulation is £1200 or so I wondered if any one out there had hit this problem before,Any thoughts much appreciated

 

[Softus]

I've been asked to quote for heating an office space-new build-it should be having underfloor heating-but there is only room for 75 mm absolute max screed,as is common practice,the insulation is under the slab.The buider has been told that this is ok as the slab willbecome part of the thermal mass.

Was it the underfloor heating equipment manufacturer who told the builder this? If so, then I think I'd choose a different product, because I think it's wrong information, or you're being duped.

Is it possible that the builder is making it up to suit his own purposes? I have found that a very tiny percentake of builders are manipulative liars. Some are even good at it.

Bottom line: choose the product according the needs, and follow the manufacturer's installation instructions to the letter. And talk to them if those instructions are at all unclear or ambiguous.

If you don't do this, and there is a problem with what you install, the liability will be yours and nobody elses. Unless you have it writing that the builder is fully liable.

 

[mikethepipe]

Thanks softus.I certainly won't be doing anything that compromises speedfit's advice,I have always found their technical support 1st class.
My suspiscions were confirmed today when I dropped the quote round-myself and another plumber,around £8 k-apparently builders mate-£5k!
Good luck to him-the combi alone is £1400+.'nother lesson learnt-or at least 'till the next one!

 

[Balenza]

Mikethepipe wrote

,

as is common practice,the insulation is under the slab

Not on new builds it aint.
The concrete subfloor is laid with a radon barrier between it and the aggregate stone usually about 150mm below finished floor level.
All the building work is completed then the insulation is laid in preparation for the sand/cement screed.

The buider has been told that this is ok as the slab willbecome part of the thermal mass.

Who told him this ?
Any UF edge insulation used ?. I doubt it.
Laying manufacturers matting will be pretty much useless to prevent downward heat flow. Without the necessary edge insulation the heat simply conducts straight out through the concrete blocks and into the cavity plus you are increasing the response time ten fold.
You should go for a minimum of 60mm high density insulation below the sand/cement screed on new builds where the floor is heated up to provide space heating and the appropiate edge insulation used.

 

[mikethepipe]

Sorry prob giving you the wrong impression,def been on new builds where the insulation is under the oversite,then 75mm screed,maybe weird buiding in lincolnshire! Anyhow as you say -by the book or not at all

 

[Balenza]

Mikethepipe wrote

oversite

By this you mean "subfloor".

So is their any edge insulation used where UF heating is being proposed ?.

 

[Balenza]

Figure 2 on this link is how its done round our way.

http://www.swale.gov.uk/media/adobepdf/building_approval_floors.pdf

Figure 1 is not a good design where UF heating is being proposed. Though edge insulation is shown in the diagram.

 

[mikethepipe]

Balenza,sorry if wrong term-plumber not builder-speedfit reccomend mutilayer foil type insulation -7mm thick which you turn up at the edges,so you isolate and insulate the thermal mass from the concrete underneath,and although this stuff is £200.00 for 20 sq.m.,it would seem to be the only answer.thanks for your help and interest