150mm concrete screed with underfloor heating

butsy1981

Hi All,

To save money in our build our architect suggested doing the ground floor in a single concrete pour of 150mm. We are putting in ufh with a geothermal heat pump. My concern is how a screed this thick will work with UFH as I've not heard of any examples at this thickness. His reasoning is that it may take longer to heat but will retain heat longer and will work well with always on nature of geothermal. I'm getting the opinion of the geothermal installer tomorrow but was curious if others had any experiences of screeds this thick with ufh. The floor and foundation spec is:


- 150mm concrete screed powerfloated finished floor on 125mm Xtratherm Thin R Underfloor Insulation on radon barrier Dpm on minimum 150mm well consolidated hardcore in layers not exceeding 225mm

fclauson

You should get this checked by an engineer - it does not sound right to me

Victor

If there is a builder involved, it is his or the geothermal installer's suggestion, not the architect's. The saving comes from finishing the concrete only once and the slight saving in concrete. Given that we are heading into rainy season, do you want to delay laying the concrete?

butsy1981 wrote: »

His reasoning is that it may take longer to heat but will retain heat longer and

If the alternatives are:
- 150mm concrete screed powerfloated finished floor on 125mm Xtratherm Thin R Underfloor Insulation on radon barrier Dpm on minimum 150mm well consolidated hardcore in layers not exceeding 225mm
- 50mm concrete screed powerfloated finished floor on 100mm concrete on 125mm Xtratherm Thin R Underfloor Insulation on radon barrier Dpm on minimum 150mm well consolidated hardcore in layers not exceeding 225mm

Then:
(a) you are heating the insulation more than previously and the concrete less. It will take a minimum 50% longer to feel the heat.
(b) it will not retain heat longer - there is the same mass of material involved. Where would the extra heat be kept?
(c) if there is a problem down the line, you have to dig up the whole floor, not just the screed.

Geothermal may be always-on, but you are still paying for the electricity.

fclauson

firstly 125mm is not enough - go for 200mm - check you DEAP/BER numbers

Also - in a well insulated house that screed will never move in temp - mine stays in the rang 20 to 23 all year round

BryanF

fclauson wrote: »

firstly 125mm is not enough - go for 200mm - check you DEAP/BER numbers

+1 and get your arch to check the building regs governing underfloor heating u-value requirements

DOCARCH

So as not to freak the OP out completely...:)...in theory, 125mm of the insulation specified should give you a u-vlaue of 0.15 (which is the minimum B Reg requirement for UFH).

But, as suggested above, have your arch/eng confirm/calculate your specific requirement in relation to the actual size of your proposed floor slab (perimeter : area ratio).

sydthebeat

butsy1981 wrote: »

Hi All,

To save money in our build our architect suggested doing the foundation in a single concrete pour of 150mm screed. We are putting in ufh with a geothermal heat pump. My concern is how a screed this thick will work with UFH as I've not heard of any examples at this thickness. His reasoning is that it may take longer to heat but will retain heat longer and will work well with always on nature of geothermal. I'm getting the opinion of the geothermal installer tomorrow but was curious if others had any experiences of screeds this thick with ufh. The floor and foundation spec is:


- 150mm concrete screed powerfloated finished floor on 125mm Xtratherm Thin R Underfloor Insulation on radon barrier Dpm on minimum 150mm well consolidated hardcore in layers not exceeding 225mm

why is the word 'foundation' in here??

a 150 concrete slab would certainly not be enough to act as a raft foundation, you MUST get this checked with your engineer.

the standard spec for UFH when theres a raft foundation is:
UFH in 75mm screed
150 PIR insulation
radon
Raft foundation as specified by engineer
consolidated hard core.


In what you have speciifed:
1. the insulation and UFh would actually be outside of the house structure :eek:
2. i highly doubt 150mm is strong enough for your far foundation
3. there will be a myriad of reinforcement bars with this 150mm. How would they fit the UFH??
4. the insulation would have to be load bearing XPS type, costs a fortune.


please clarify exactly what the specification for foundation and floor constructions are.

butsy1981

sydthebeat wrote: »

why is the word 'foundation' in here??

a 150 concrete slab would certainly not be enough to act as a raft foundation, you MUST get this checked with your engineer.

the standard spec for UFH when theres a raft foundation is:
UFH in 75mm screed
150 PIR insulation
radon
Raft foundation as specified by engineer
consolidated hard core.


In what you have speciifed:
1. the insulation and UFh would actually be outside of the house structure :eek:
2. i highly doubt 150mm is strong enough for your far foundation
3. there will be a myriad of reinforcement bars with this 150mm. How would they fit the UFH??
4. the insulation would have to be load bearing XPS type, costs a fortune.


please clarify exactly what the specification for foundation and floor constructions are.

My mistake I shouldnt have said foundation, it's the ground floor. I posted while half asleep!

Anyway, today I've spoken to one of the geothermal installers that I'm considering. This guy is very knowledgeable and is one of the biggest and most well established in the country and reckons the Architect is correct, that 150mm over the UFH would act as a great heat storage and he has done similar in his own house. I'm awaiting a 2nd opinion from the second geothermal installer I'm looking at.

fclauson

just as reference - I have 100mm approx which holds the heat well - you can then time the HP to run 11pm->6pm on night rate - and is why I put PV in so the HP can run 10am -> 4pm during day time

Victor

fclauson wrote: »

you can then time the HP to run 11pm->6pm

6am?

fclauson

well spotted - 6am

john f 4g63

I was allowing for 150mm insulation and then putting my underfloor in to a 75mm screed but the geotherminal crowd i am thinking of going with are advising me against this. They said i would need a buffer tank if i go down this route. They reckon i should put the underfloor into concrete instead of a screed as its better for the heat pump as the concrete will be slower to react so the pump wont be start and stopping all the time.
What do people think of this?

fclauson

that depends - if you are super insulated then it makes no difference (and that is why I would put 200mm under the screed)

buffer tanks are to get around the problem of thermal leakage and the floor needing a top up

john f 4g63

Well my spec is i am having 200mm pumped cavity then using the inside walls as thermal mass, im doing air tightness and hrv. It would work out cheaper to just put the underfloor in concrete compared to screed alright but is there a minimum thickness of concrete id want around the pipes?
The problem now is i have 225mm between my subfloor and finished floor so i cant fit the 200mm insulation now or id have only 25mm left for underfloor.

fclauson

I will leave it to my learned experts and more importantly your importantly engineer about what is possible

but in your first post you said but can you have a 275 (150mm screed on 125 insulation)

So that should give you 200mm insulation & 75mm screed

You have to do the maths - does a large lump of concrete poorly insulated perform better than a thinner bit well insulated

how have you thermally broken the walls from the foundation ? - did you do a couple of rows of quinn

I went for every room a 1inch/50mm up stand of insulation around the walls - thus each room is a "tray" of concrete -

I wish (and I had done the same at he door ways ans I have had some cracking there even though corriboard or similar was used to separate each room off - but you screen layer should help with that

Edit - you floor is the largest surface area of a build which is constantly connected to a surface which will always be at around 8 degrees (typical temp of soil at 1ft down) - so make sure you insulate well from it

THE DON FANUCCI

ground floor detail: I'm going with 150mm insulation board, UFH pipework clipped onto the insulation board/ then pour 150mm concrete floor on top of top.

any negatives or positives with this guys?

(before anybody asks no i haven't ran it by the engineer just yet. coz he's on holidays.)

butsy1981

Im no expert but as stated when i posted this originally we did go with the 150mm screed in the ground floor and 70mm on first floor on ducon slabs. It works extremely well with our geothermal heat pump. I have it set to heat the house during the night on the night rate and it retains the heat throughout the day and very rarely needs to come on by day. The house is always a nice even temperature its very cost efficient when paired with our heatpump.

THE DON FANUCCI

butsy1981 wrote: »

Im no expert but as stated when i posted this originally we did go with the 150mm screed in the ground floor and 70mm on first floor on ducon slabs. It works extremely well with our geothermal heat pump. I have it set to heat the house during the night on the night rate and it retains the heat throughout the day and very rarely needs to come on by day. The house is always a nice even temperature its very cost efficient when paired with our heatpump.

cool. I'm going with air-to-water heat pump so i presume it will do the same for me?
yes i'm going with slabs first floor also and 70mm screed.

i was very cautious maybe the 150mm was too thick to let the heat through.

hexosan

Why not do 200mm insulation 100mm screed.

BarneyMc

hexosan wrote: »

Why not do 200mm insulation 100mm screed.

I think this would be a better option also. 100mm screed is plenty for thermal mass and heat retention.

THE DON FANUCCI

what about 150mm insulation and 100mm screed? would this be ok you reckon

BarneyMc

THE DON FANUCCI wrote: »

what about 150mm insulation and 100mm screed? would this be ok you reckon

I thought you had 300mm to play with?

THE DON FANUCCI

BarneyMc wrote: »

I thought you had 300mm to play with?

its the cost v structural v insulation balance i'm trying to get right.

i can go with 250-300 either way really but i'm wondering is there a structural obligation to put in 150mm of concrete?
I know i will def need 150mm of insulation board that has been said by my energy guy.
so i'm just sizing up how much concrete over my ufh so it will conduct through ok. 6 inchs sounds like alot

BarneyMc

THE DON FANUCCI wrote: »

its the cost v structural v insulation balance i'm trying to get right.

i can go with 250-300 either way really but i'm wondering is there a structural obligation to put in 150mm of concrete?
I know i will def need 150mm of insulation board that has been said by my energy guy.
so i'm just sizing up how much concrete over my ufh so it will conduct through ok. 6 inchs sounds like alot

4 inches is plenty. If you have 300mm then 200 EPS and 100 concrete is just right. 75 concrete would work well also.

THE DON FANUCCI

BarneyMc wrote: »

4 inches is plenty. If you have 300mm then 200 EPS and 100 concrete is just right. 75 concrete would work well also.

Damp proof course/radon barrier/
150mm pir board xthratherm
underfloor heating pipes pinned to that
then 100mm concrete powerfloated floor

I think that will be a tidy, clean, cost effective, solid, well insulated job.

I will propose that to my engineer when hes back

sydthebeat

BarneyMc wrote: »

4 inches is plenty. If you have 300mm then 200 EPS and 100 concrete is just right. 75 concrete would work well also.

in all this are we assuming there is or is not a concrete subfloor?

BarneyMc

sydthebeat wrote: »

in all this are we assuming there is or is not a concrete subfloor?

There is.

sydthebeat

BarneyMc wrote: »

There is.

perhaps the don can clarify because i dont see that mentioned in this thread.

THE DON FANUCCI

no concrete sub floor

sydthebeat

THE DON FANUCCI wrote: »

no concrete sub floor

Then your engineer will have a huge say into what depth of concrete can be poured into what level of insulation.

hexosan

You need concrete sub floor (to engineers spec)
150mm PIR/200mm eps (cheaper). If you can get 200mm PIR/250mm EPS better
75mm concrete screed or 50mm liquid screed

hexosan

Don I have to say I'm all for helping people out but it does seem like your making this whole build up as you go.
All the cost saving/corner cutting you trying to do now will cost you in the long run.

THE DON FANUCCI

so you always need to pour a concrete sub-floor for underfloor heating?

butsy1981

I can pm you a pic of my floor before the 150mm pour. No concrete sub floor. 1 big pour. I was nervous too about how this extra thick layer would work with my ufh. But my builder, architect and 3 different geothermal installers recommened it. Its slower to heat up initially but retains more heat and because im using geothermal its kept at a fairly steady temperature all day and night. Id be alot more wary of doing something like this if using oil driven ufh as youd tend to turn if off and on alot more and it would take a while to heat up. As with most new builds my house is well insulated a3 rated, 6 inch pumped cavity, tripple glaze and very airtight though not passive and i dont have heat recovery. I find when the weather chages suddenly and gets very cold outside the house doesnt take long to adjust. Overall im very happy with my setup and its very cheap to run and great to have no more oil bill!

In saying all this, im no expert and would advise talking to your heatpump installer, engineer or architect. Though a bit like these boards youll find everyone has different opinions on these things which is the real head melting thing about building. Anyway best of luck

THE DON FANUCCI

butsy1981 wrote: »

I can pm you a pic of my floor before the 150mm pour. No concrete sub floor. 1 big pour. I was nervous too about how this extra thick layer would work with my ufh. But my builder, architect and 3 different geothermal installers recommened it. Its slower to heat up initially but retains more heat and because im using geothermal its kept at a fairly steady temperature all day and night. Id be alot more wary of doing something like this if using oil driven ufh as youd tend to turn if off and on alot more and it would take a while to heat up. As with most new builds my house is well insulated a3 rated, 6 inch pumped cavity, tripple glaze and very airtight though not passive and i dont have heat recovery. I find when the weather chages suddenly and gets very cold outside the house doesnt take long to adjust. Overall im very happy with my setup and its very cheap to run and great to have no more oil bill!

In saying all this, im no expert and would advise talking to your heatpump installer, engineer or architect. Though a bit like these boards youll find everyone has different opinions on these things which is the real head melting thing about building. Anyway best of luck

please PM me that floor make up.

stickybookmark

THE DON FANUCCI wrote: »

ground floor detail: I'm going with 150mm insulation board, UFH pipework clipped onto the insulation board/ then pour 150mm concrete floor on top of top.

any negatives or positives with this guys?

(before anybody asks no i haven't ran it by the engineer just yet. coz he's on holidays.)

What you describe here is the the GF make up that I have.

My GF: 150mm concrete with UF pipes on vapour layer on 150mm insulation (80 +70) on radon barrier on 50mm sand blinding on 225mm hardcore.

Planning on running GSHP on night-rate for all heating and hot water needs and the concrete will act as a heat well

THE DON FANUCCI

stickybookmark wrote: »

What you describe here is the the GF make up that I have.

My GF: 150mm concrete with UF pipes on vapour layer on 150mm insulation (80 +70) on radon barrier on 50mm sand blinding on 225mm hardcore.

Planning on running GSHP on night-rate for all heating and hot water needs and the concrete will act as a heat well

do you think the heat will conduct fine through 6 inchs of concrete ya? I hope to go with this plan but with air-to-water

fclauson

Mine (PH certified) is

90 screed with UFH
200MM insulation
concrete sub floor 150mm
radon barrier
Sand blinding
Hardcore

In additional around EACH ROOM is a 50mm wide upstand to insulate the screed from the walls (i.e .the screed sits in an insulated tray effectively)

Whole house is one heating zone - no thermostats

screed heated by HP at night only - @ around €150 per annum heating costs (50c per Sq M)

THE DON FANUCCI

fclauson wrote: »

Mine (PH certified) is

90 screed with UFH
200MM insulation
concrete sub floor 150mm
radon barrier
Sand blinding
Hardcore

In additional around EACH ROOM is a 50mm wide upstand to insulate the screed from the walls (i.e .the screed sits in an insulated tray effectively)

Whole house is one heating zone - no thermostats

screed heated by HP at night only - @ around €150 per annum heating costs (50c per Sq M)

is that air-to-water of ground source hp? jesus that a lot of concrete. 150e per year is excellent

fclauson

Air to Water - in Ireland with a mean outside air temp of around 6C the benefits of Ground source are limited - and given it costs around 2 to 3K extra to install the pay back in my case would have bee 25 years !!

THE DON FANUCCI

fclauson wrote: »

Air to Water - in Ireland with a mean outside air temp of around 6C the benefits of Ground source are limited - and given it costs around 2 to 3K extra to install the pay back in my case would have bee 25 years !!

should heat pumps be run on night rate? is it much cheaper? how do I set it up it to run it at night rate I know nothing about night rate or esb rates

BarneyMc

fclauson wrote: »

In additional around EACH ROOM is a 50mm wide upstand to insulate the screed from the walls (i.e .the screed sits in an insulated tray effectively)

I assume some of that 50mm was covered by the wall plaster & skim and skirting? But was there some upstand insulation showing when your tiler had to tile your floors and did it work out alright? I would like to use 50mm perimeter insulation also but a bit weary about causing a problem down the line for my tile/laminate laying. Thanks.

BarneyMc

THE DON FANUCCI wrote: »

should heat pumps be run on night rate? is it much cheaper? how do I set it up it to run it at night rate I know nothing about night rate or esb rates

Some run pumps at night only, others let it run when it needs to but depends on lots of things like if there's a high level of occupancy during the day, etc.

It's half price at night but there's about an extra €50 a year in standing charges. You just need to specify a dual tariff meter when applying to the ESB.

fclauson

BarneyMc wrote: »

I assume some of that 50mm was covered by the wall plaster & skim and skirting? But was there some upstand insulation showing when your tiler had to tile your floors and did it work out alright? I would like to use 50mm perimeter insulation also but a bit weary about causing a problem down the line for my tile/laminate laying. Thanks.

The upstand was cut flush with the finished floor level so tiles go across the top and the plaster & skirting are not affected

BarneyMc

fclauson wrote: »

The upstand was cut flush with the finished floor level so tiles go across the top and the plaster & skirting are not affected

Sorry, I mean having part of the tile/laminate on top of the insulation - did that make the tile/laminate unstable in any way?

stickybookmark

THE DON FANUCCI wrote: »

do you think the heat will conduct fine through 6 inchs of concrete ya? I hope to go with this plan but with air-to-water

Before pouring the floors we contacted the 2 HP suppliers we were looking at.
One said GSHP would ''love'' the concrete depth but A2W ''might struggle''.

The other said both GSHP and A2W would run fine with it.

THE DON FANUCCI

some people using 4inch sub floor and 3 inch screed.
some people using 6inch screed finished floor.

why don't people just use 4 inchs finished floor and no subfloor and no screed?

sydthebeat

THE DON FANUCCI wrote: »

some people using 4inch sub floor and 3 inch screed.
some people using 6inch screed finished floor.

why don't people just use 4 inchs finished floor and no subfloor and no screed?

ask your engineer

THE DON FANUCCI

sydthebeat wrote: »

ask your engineer

he's on holidays.
looking for opinions from people before I say it to him.
I can't see why 4 inchs wont work

sydthebeat

THE DON FANUCCI wrote: »

he's on holidays.
looking for opinions from people before I say it to him.
I can't see why 4 inchs wont work

Don, in all due respect, its not for you to say to him how your going to build it, nor is it for you to question why 4inches wouldnt work.

There are engineering standards required, and these standards are applicable at different levels in different specific cases. Just because something may have worked for another poster does not mean that it will automatically work for you.

what you are doing now is questioning a structural factor of the build, and those questions are not permitted here for, among others, the reasons ive outlined above.

THE DON FANUCCI

just heard back from engineer.

He says underfloor heating in four inchs of concrete is fine. this will be my finished powerfloated floor. no need for subfloor and no need for 75mm screed.

underneath will be minimum 225mm well compacted hardcore of course and dpc and 150mm insulation. job done.
sounds good to me.