underfloor heating (wet type)

[teddyb]

Hi

I would like some clarification please, if someone can help .....

builder has laid 100mm concrete (on dpc), is going to lay 100mm insulate then the plumber is going to lay the piping for the heating. Builder is to come back to 50mm screed. We went to order porcelin floor tilesd today and were advised that the adhesive used must be flexible, so that's what we ordered. On the way home I though: "why do we need flexible adhesive if there is 50.. screed on top of the heating pipes?"

Is the 50mm screed necessary?

Any thoughts gratefully accepted,
Cheers

 

[Gasguru]

The 50mm screed gives the underfloor pipework "thermal mass". It allows the temperature to remain more stable and gives better control despite doors opening (draughts) etc.

Being a sand/cement screed as it heats and cools it will expand/contract perhaps creating small cracks in its structure. The flexible adhesive helps prevent the tiles cracking as well. Has a decoupling membrane been mentioned? These are bonded to the screed and then the tiles bonded on top. It helps prevent the cracks in the screed coming through to the tiles.

 

[Slugbabydotcom]

1.To allow for expansion and contraction

2.Yes.

 

[teddyb]

Thank you both ... I feel a lot more confident now!

 

[bengasman]

Your builder actually seems to know what is needed, and is doing a proper job. Certainly rare around here. Say thank you and give the boys lots of tea and coffee.

 

[htgeng]

Your builder actually seems to know what is needed, and is doing a proper job. Certainly rare around here. Say thank you and give the boys lots of tea and coffee.

Yes 100mm of insulation is a very good standard. It might be worth being nosey and check the plans to ensure there is a perimeter of insulation around the screed to prevent thermal bridging.

The people who supply the underfloor heating often throw in a roll of insulation for this purpose. Throw that in the bin as it is useless. Sawn strips of 50mm kingspan laid along all the walls provide excellent insulation to stop all the heat being sucked out the slab.

When the screed is dry the excess insulation can then be trimmed off at floor level. The the tiles can be laid as normal over the whole floor.