Underfloor Heating & the Finished Floor

Jorus

We are trying to decide whether to put underfloor heating in now directly on the sub floor or else wait until the blocks and roof are up and put it in after and pump screed in on top of it.

We are putting in 75mm of insulation under the UH pipes and then 50mm of screed/concrete.

If we go ahead and do the UFH and the finished floor now with 50mm of concrete on top as the finihsed floor - will the finished floor be able to take the weight of bales of blocks on top of it (as the block layer will need them placed on the floor before he starts working on the walls (the internal walls will be block also).

It would be cheaper and easier to put it in now as it would use alot less pipping, however we are concerened that the floor will not hold the weight of the blocks.

Any advice?

Thanks

RKQ

I would expect a 50mm screed on 75mm insulation to crack, IMO.
You could be lucky and it might not.

Try laying 8 x 4 ft sheets of cheap ply, over the floor, to support the blocks.
The blocks will only be on the floor for afew days.

It will be cheaper to lay the screed now.
However, You could consider a sand/cement screed, laid after the blocks are built. The screed is supplied by truck. It can be wheel-barrowed in and laid quickly. It can be levelled by spot levels.

Jorus

Thanks for the reply,

I suppose the whole reason we are looking into doing the UFH and finished floor now rather than later is because not only would the concrete be cheaper to do now rather than pumped screed but also not as much pipes for the underfloor would be needed.

Could save quite a few grand, but then we dont want the floor to be cracked and ruined either.

RKQ

Hi Jorus, price a sand/cement screed with your local Concrete supplier. I've seen 4 Screeders lay 1350sqft screed in 5 to 6 hours. Perfectly level for porcelain tiles. Labour circa $750.

Sand/cement screed is very good for underfloor heating.
It is also softer, less brittle that concrete. So it would be easier to dig up if a pipe bursts!

Put light mesh in the screed to help prevent cracks. ( I did see "chicken wire" used sucessfully in thin screeds.)

Best of luck!

bertie1

Why not leave pouring the floor screed until the blockwork & plastering is finished , that way the pipes or the floor cannot get damaged by any of the trades

BadCharlie

Same problem came up when i was doing my house. The people who were putting in my heating system wanted me to do my final pipe work and insulation and screed at the end of project. Don't know why but i think he should not have told me what to do and let me pick what i wanted to do.

I did in the end go for
100mm Conc with iron mesh in it.
Built the walls did the roof and lots more.
Then came back put 75mm insulation, had to then put a layer of plastic over the insulation before pipe work for my underfloor heating went down. Why you need to plastic down is for the easy screed will run under your insulation and also maybe leak out of your house.
Then after pipe work, easy screed another 40mm i think it was. Worked fine with no cracks or any damage. Now all my floors are either tile or wood.

Also you should think about what floor finish you want ? as it will effect the heat from coming up.
Also u need the deapth for your extra insulation, screed and floor finish in mind before you do anything.

Jorus

BadCharlie,

The company that is doing our UFH is trying to convince us the opposite of what you were told - they want us to do the insulation & UFH pipes etc now before we build the walls up - but after reading the replies etc i think we are better waiting until after the walls and roof are on and that way the floor and screed will not get damaged. It will cost extra in piping and also for the pumped screed but better safe than sorry

In relation to your insulation 75mm and screed - were you happy with that amount?
We are pouring the sub floor next week and we have provided for - putting down 75mm Xtraterm insulation and then we will be pumping in 50mm of the sand/concrete screed over the UFH pipes (defo will be putting plastic down too). Is this enough ?

RKQ

Jorus I am getting confused?
The UFH company might want your to pour before the walls because

• Its easy to use the rising walls to level and powerfloat the floor slab.
• They want their money asap. Sooner you lay pipes the better for them.

If you are pouring your sub-floor slab next week the try to lower the sub-floor to get a thicker finished floor, maybe 100mm foil insulation and 75mm screed. ( Screen is a sand and cement mix, it is not concrete)

Sand & cement screed can be wheelbarrowed into the house or poured in throught patio door ope and ground floor windows. It is fast to lay as it comes relatively dry (looks abit like grey sand) It will not be sloppy and runny like concrete. It is ideal for underfloor heating.

Finally, what is heating your UFH? If Oil use a thin 50mm screed that will heat up quickly and loose heat quickly. If geothermal, then use a thicker screed. I have 100 - 125mm for geothermal. It takes longer to heat up but it stores heat longer, important if heating with cheap rate electricity, at night!

Personally I'd recommend at least 75mm, as unless your sand blinding, sub-floor, insulation etc is "perfectly" level, you might find it difficult to get 50mm everywhere. (Being out by 10 - 25mm is not unusual in the real world. Building isn't an exact science, there are tolerances)

Jorus

hi rkq,

I meant to say sand/cement -sorry

We will be heating the UFH with gas condensing boiler - would 75mm screed be a bit too thick for this?

I dont think we will have enough for 100mm insulation and also 75mm screed -
What would be the best alternative?


Cheers

BadCharlie

RKQ knows his stuff.

After what i did i wish i did it differint to be honest.

I wanted to do it the way your heating company is telling you. To do pipe work now ect... makes it much easyer to screed and should work out cheaper by a few k i would think. (mine was self build so i did lots of the work my self) When i used easy screed i had to pay them, if i had done the job at the start of my project i would have done it my self and saved lots.

With Xtraterm floor insulation you can only get 80mm for floors in that product. I used 75mm but knowing what i know now. I wish i just used 2 50mm Xtraterm sheets. This would give me 100mm in the floors. Also i only did 40mm Easy screed and this cost me about €5,500, reading more about it i should have gone 50mm at least and 75mm is the norm. But cause i had such a big area and the costs of it all i skimped and took a chance but i was lucky "so far ".

So sum it up what i should have done.
Hardcore.
Sand beding.
Radon.
100mm Slab with mesh.
2x 50mm Xtraterm insulation ( or more as this is very important with UFH ) Also 25mm Xtraterm at sides in each room. I only did 12mm i think...
Plastic 500gage layed on insulation.
UFH pipe work.
50mm to 75mm Easy screed. Or if screeding off with walls you can use ready mix & not easy screed. Readymix also have a differint kind of mix for UFH slab which you should ask for.

BadCharlie

Jorus wrote: »

hi rkq,

I meant to say sand/cement -sorry

We will be heating the UFH with gas condensing boiler - would 75mm screed be a bit too thick for this?

I dont think we will have enough for 100mm insulation and also 75mm screed -
What would be the best alternative?


Cheers

Get your block layers to come back and do another Row of blocks ?
If you have a contractor tell him, or if its self build you can do these changes. I know i did this my self and its fine.

Only a suggestion on what you could do if you found you did not have the space.