Floor screed and underfloor heating

mccleanp · 30-04-2009 10:48PM #1

I will soon be ready to lay floor insulation and screed.

On the ground floor, I had planned 2x60mm Kingspan (or similar) with 80mm of sand/cement screed, giving a finished floor height of 200mm above the subfloor slab.

On the 1st floor, I had planned 70mm Kingspan and 80mm of sand/cement screed, giving a finished floor height of 150mm above the concrete slab.

I am installing underfloor heating and have recently found out about products such as easyscreed, which appear to offer better performance with underfloor heating, with less depth.

Does easyscreed offer much advantage of traditional sand/cement screed?

My finished floor levels are not negotiable because I have a concrete staircase already installed. Can I still consider easyscreed type products? What depths of insulation and screed would you suggest?

Due to budgetary constraints, we will likely move in on top of unfinished floors (i.e. no floor tiles) for 6-12 months. How would the different screeds hold up in these circumstances?

sinnerboy · 30-04-2009 11:20PM

Easi screed can be installed as thin as 35mm . It is literally poured into place and with very little effort achieves a flat smooth finish . Because of its relative lack of mass vs concrete screed your UFH would respond more quickly i.e. heat up faster

http://www.screedflo.ie/video.htm

Thats the "pro"

It costs about twice the price . It is not very durable - un finished. It requires the protection of a floor finish ( tile/carpet/timber ) . I'm not saying it is delicate or fragile . But even the guys who sell it ( I don't by the way ) will tell you that it should not be left un finished for too long . It should not be used in very wet areas - i.e. no problem in bathrooms , kitchens etc - but not in "wet room" type bathrooms .

If you go with it you can increase the insulation thickneses BUT - the insulation layer below should not be thicker than 60mm - those boards can curl and the lack of mass can then cause the screed to also curl .

If you decide to stick with concrete screed you can take it's thickness down to - but not less than 65mm - in fact it is better to do so so you do not unduly affect the heating reponse period.

Whatever screed you use do not forget to use an edge strip of insulation between the enclosing walls and the screed

wardwil · 01-05-2009 01:32AM

Hi All,

I am in a similar position. Laying 50mm of easy screed. This is a first for me to hear about the wet rooms. I am having two in the house. Will I have problems and should I just leave out these rooms from the easy screed and just use the concrete screed?

Excuse the ignorance but what do you mean by the insulation? I don't understand why leaving the gap?

Thanks... these boards have proved invaluable.

sinnerboy · 01-05-2009 09:32AM

I got that advice about wet rooms from a Dublin easy screed provider . So check ( and double check ) with your provider . It may not be true in all cases

The insulation .... is what must be laid immediately below ANY UFH screed . A common mistake is to locate the floor insulation below the concrete sub floor - do not do this ever .

I don't understand you question about "leaving the gap" . I did not suggest this .

Lightning McQue · 01-05-2009 09:48AM

Folks

I am just wondering about the 70mm of insulation on the first floor. Is this correct?

It seems excessive.

I thought 40 mm of kingspan was sufficient upstairs on the concrete floor?

Can someone confirm that this is correct please?

Thanks.

Lightning

mccleanp · 01-05-2009 10:05AM

The reason I was intending to use 70mm upstairs (and 120mm) downstairs was that the plans were originally drawn for 50mm upstairs and 100mm downstairs with 100mm screed on top in both cases.

When I got my UFH engineer engaged, he suggested reducing the screed depth to 80mm, resulting in the additional insulation. Extra insulation cannot be a bad thing surely?

I would be a little concerned about using easyscreed and reducing screed depth and increasing insulation depths even further. Would the insulation compress over time resulting in the floor dropping and cracking?

I also have a couple of wetrooms to consider.

Sinnerboy, you recommend using no more than 60mm insulation. Do you mean no more than 60mm in a single sheet (i.e. 2x60mm is ok)? Would you suggest splitting the 70mm upstairs insulation into 2 layers (e.g. 30mm + 40mm)?

sinnerboy · 01-05-2009 01:04PM

Lightning McQue wrote: »

Folks

I am just wondering about the 70mm of insulation on the first floor. Is this correct?

It seems excessive.

I thought 40 mm of kingspan was sufficient upstairs on the concrete floor?

Can someone confirm that this is correct please?

Thanks.

Lightning

Correct . There is no heat loss to the floor level below and so in this case 40mm would be fine

sinnerboy · 01-05-2009 01:10PM

mccleanp wrote: »

The reason I was intending to use 70mm upstairs (and 120mm) downstairs was that the plans were originally drawn for 50mm upstairs and 100mm downstairs with 100mm screed on top in both cases.

When I got my UFH engineer engaged, he suggested reducing the screed depth to 80mm, resulting in the additional insulation. Extra insulation cannot be a bad thing surely?

Within reason - no . More insulation is better .

mccleanp wrote: »

I would be a little concerned about using easyscreed and reducing screed depth and increasing insulation depths even further. Would the insulation compress over time resulting in the floor dropping and cracking?

No . Take a PIR board on stand on it - with ply over to avoid point loading it . Very tough in compression .

mccleanp wrote: »

I also have a couple of wetrooms to consider.

Make this known to the easi screed people

mccleanp wrote: »

Sinnerboy, you recommend using no more than 60mm insulation. Do you mean no more than 60mm in a single sheet (i.e. 2x60mm is ok)?

yes

mccleanp wrote: »

Would you suggest splitting the 70mm upstairs insulation into 2 layers (e.g. 30mm + 40mm)?

you have 150mm so I would go for - 50 easi screed + 2 x 50 insulation

Or

70mm concrete screed + 80mm insulation

windyboy · 18-05-2009 11:52PM

Hi Guys,

Interesting thread, I was at the self-build show in Galway last week got a brochure on www.screedfo.ie. It seems to be an impressive product, has anyone here installed it with underfloor heating whats your experience with the company?

I am building a house in KORE ICF. We have decided on installing underfloor heating in the ground floor. We were also thinking of 150mm subfloor, insulate using silver 200mm EPS KORE floor, with 50mm screed Screedflo.

http://www.kore-icf.com/koreFiles/pdf/KORE_Floor_Technical.pdf

I was wondering if anyone else has used this type of makeup, would it be ok? and if we do go with wet rooms in some of the bathrooms what advice would you have?

Thanks,
Windboy

exaisle · 21-05-2009 08:37PM

Hi,

I used Screedflo. The guys turned up when they said they would (major bonus in my book) and had finished the job in around 5 hours. (Ground floor is about 1800 sq ft).

I'm very happy with the job....and would recommend. Although it was probably twice the price of a standard sand/cement, it was worth every cent and saved a lot of time and hassle when laying tiles (eg. bathrooms, kitchen) or timber flooring (bedrooms, living rooms etc).

Aside from being a satisfied customer, I have no other affiliation with screedflo.ie

E.

sinnerboy · 21-05-2009 09:08PM

windyboy wrote: »

I was wondering if anyone else has used this type of makeup, would it be ok? and if we do go with wet rooms in some of the bathrooms what advice would you have?

Thanks,
Windboy

Have not used that exact make up - but I have used thins screeds ( not that one ) with great success .

The very nature of these screeds is they finish beautifully flat - not what you want in a wet room . So in order to make those floors to fall to drain - you will need to form a step up at the doorway with a layer of ordinary sand + cement screed which you can shape to fall .

redonly · 22-06-2010 02:21PM

exaisle wrote: »

Hi,

I used Screedflo. The guys turned up when they said they would (major bonus in my book) and had finished the job in around 5 hours. (Ground floor is about 1800 sq ft).

I'm very happy with the job....and would recommend. Although it was probably twice the price of a standard sand/cement, it was worth every cent and saved a lot of time and hassle when laying tiles (eg. bathrooms, kitchen) or timber flooring (bedrooms, living rooms etc).

Aside from being a satisfied customer, I have no other affiliation with screedflo.ie

E.

hello exaisle

just wondering did you have any problems with flloor coverings on your screed?

AdamAntsy · 23-06-2010 12:44PM

Related question - does the thickness of the sand & cement screed have a impact on the performance of the UFH?

Specifically - my engineer is spec'ing a 100mm screed on the lower floor and I'd be worried that this may negatively impact the UFH performance.

NickTellis · 10-08-2011 08:35AM

AdamAntsy wrote: »

Related question - does the thickness of the sand & cement screed have a impact on the performance of the UFH?

Specifically - my engineer is spec'ing a 100mm screed on the lower floor and I'd be worried that this may negatively impact the UFH performance.

Same here. Is there much of a "warm-up" time difference between a 75 mm and a 100 mm screed depth? Presumably there will be but also presumably the heat will be retained for longer. Anyone any experience with this?

YMCA · 11-06-2012 01:46PM

NickTellis wrote: »

Same here. Is there much of a "warm-up" time difference between a 75 mm and a 100 mm screed depth? Presumably there will be but also presumably the heat will be retained for longer. Anyone any experience with this?

I was just wondering the same thing as I am planning on pouring 100mm of concrete on my UFH. Will it mean heat will retain longer or not get out at all?

mark11original · 22-09-2016 11:27PM

Hi, just wondering anyone have any update on 100mm of concrete on top of the UFH pipes? I am thinking of using the Kore passive foundation and it calls up for 100mm of concrete.

Paul Kiernan · 23-09-2016 02:51PM

mark11original wrote: »

Hi, just wondering anyone have any update on 100mm of concrete on top of the UFH pipes? I am thinking of using the Kore passive foundation and it calls up for 100mm of concrete.

I'm doing the same and I think the additional thermal mass is a good thing, especially as I'll have a relatively lightweight timber frame. With 300mm EPS you won't "lose" any heat, it'll just take longer to heat up and cool down. See here for what I'm talking about.

mark11original · 24-09-2016 03:03PM

Ya same idea as myself - just a different supplier of the passive slab and blockwork for the house. Just wasn't sure would the 100mm of concrete be a disadvantage, I know it takes longer to heat up and cool down, but hope it won't affect the heating bills. Hopefully it can run at a lower temp because of a larger thermal mass.

Calahonda52 · 24-09-2016 04:09PM

Paul Kiernan wrote: »

I'm doing the same and I think the additional thermal mass is a good thing, especially as I'll have a relatively lightweight timber frame. With 300mm EPS you won't "lose" any heat, it'll just take longer to heat up and cool down. See here for what I'm talking about.

Why do you thing decrement delay is relevant here?

mark11original wrote: »

Ya same idea as myself - just a different supplier of the passive slab and blockwork for the house. Just wasn't sure would the 100mm of concrete be a disadvantage, I know it takes longer to heat up and cool down, but hope it won't affect the heating bills. Hopefully it can run at a lower temp because of a larger thermal mass.

Why do you think a higher thermal mass will allow a lower temp in the UFH?

Paul Kiernan · 24-09-2016 05:48PM

Calahonda52 wrote: »

Why do you thing decrement delay is relevant here?

Decrement delay is a measure of the quantity of heat stored in a building. If the heat loss is, say, 100W/k, and the outside temperature is 10C lower, then the heat loss is 1kwhr per hour. With a 100 sq.m. 150mm concrete slab the thermal capacity (of that alone) is 30MJ/k which equals about 8kwhr. So if my maths is correct the temp of the slab will only drop by one eight of a degree per hour when the heat is turned off.

By comparision if your only thermal mass was timber frame wall and roof with a capacity of 0.6MJ/k the temperature would drop by 6C per hour (initial rate, as temp reduces the heat loss will reduce accordingly).

mark11original · 28-09-2016 11:27PM

wrote:

Why do you think a higher thermal mass will allow a lower temp in the UFH?

My thinking is that its just like having small radiators verses larger radiators. Could very well be wrong.

decodoitright · 22-01-2017 11:09PM

Hi mark11original, Just wondering what you decided in relation to your underfloor heating pipes, did you go ahead with the 100 mill screed. I am in the process of ordering my Passive slab and this has slowed me in my tracks a bit. Would love to hear your opinion on this, Cheers.

Floor screed and underfloor heating

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