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Is insulation needed on 1st floor concrete slab?

  • 24-01-2015 12:30AM
    #1
    Cks5
    Registered Users, Registered Users 2 Posts: 30 ✭


    Just wondering if fitting wet ufh to a 1st floor concrete slab, covering with sand/cement screed, is insulation needed?
    If not, it's going to save me approx 2k
    Is insulated plasterboard on the ground floor ceiling an option, then a 4-6" service void followed by suspended ceiling


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Comments

  • #2
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,784 ✭✭✭✭galwaytt


    Cks5 wrote: »
    Just wondering if fitting wet ufh to a 1st floor concrete slab, covering with sand/cement screed, is insulation needed?
    If not, it's going to save me approx 2k
    Is insulated plasterboard on the ground floor ceiling an option, then a 4-6" service void followed by suspended ceiling

    Absolutely it is: otherwise you're going to be heating the r/c slabs and walls before you heat the rooms............which may be never.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #3
    Cks5
    Registered Users, Registered Users 2 Posts: 30 ✭Cks5


    I have read conflicting advice on this.
    Ground floor obviously is a must or you are heating the ground, but 1st floor is different as the heat has no where to escape to only into the slab or into the service void , but the heat isn't actually leaving the house


  • #4
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,784 ✭✭✭✭galwaytt


    Cks5 wrote: »
    I have read conflicting advice on this.
    Ground floor obviously is a must or you are heating the ground, but 1st floor is different as the heat has no where to escape to only into the slab or into the service void , but the heat isn't actually leaving the house

    Conflicting - lol. It's just physics.

    But remember why the ff slabs are called 'hollow core' -it's because they are hollow (sic) and are open to the cavity (think heat path/airtightness - or the lack thereof). Remember they're on the walls (think thermal bridging). And finally, even if they were none of those things, why would you want to bury €€€€ in heating a structural part of the building, when you only need to heat the screed.

    At the end of the day though, it's up to you, you'll be paying for the fuel.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #5
    D_D
    Registered Users, Registered Users 2 Posts: 325 ✭✭D_D


    galwaytt wrote: »
    Conflicting - lol. It's just physics.

    But remember why the ff slabs are called 'hollow core' -it's because they are hollow (sic) and are open to the cavity (think heat path/airtightness - or the lack thereof). Remember they're on the walls (think thermal bridging). And finally, even if they were none of those things, why would you want to bury €€€€ in heating a structural part of the building, when you only need to heat the screed.

    At the end of the day though, it's up to you, you'll be paying for the fuel.

    But by insulating the underside of the first floor slab, are you not removing potential thermal mass?


  • #6
    BarneyMc
    Registered Users, Registered Users 2 Posts: 1,504 ✭✭✭BarneyMc


    I think the important thing here is without FF insulation it would just be too hard to control the heating of the first floor bedrooms. For example if the hollow core slab is heated then even if the heating is off at night, it will be releasing heat into the bedroom at night whether needed or not.

    Are there any recommendations to the thickness of insulation needed here - 1 to 2 inches?


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  • #7
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,784 ✭✭✭✭galwaytt


    D_D wrote: »
    But by insulating the underside of the first floor slab, are you not removing potential thermal mass?

    No, you're heating it from above.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #8
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,784 ✭✭✭✭galwaytt


    BarneyMc wrote: »
    I think the important thing here is without FF insulation it would just be too hard to control the heating of the first floor bedrooms. For example if the hollow core slab is heated then even if the heating is off at night, it will be releasing heat into the bedroom at night whether needed or not.

    Are there any recommendations to the thickness of insulation needed here - 1 to 2 inches?

    I'll defer to anyone else with better info, but I'd have thought even 50 mm is skimping it.

    Was this not worked out on your BER OP ?

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #9
    BarneyMc
    Registered Users, Registered Users 2 Posts: 1,504 ✭✭✭BarneyMc


    galwaytt wrote: »
    I'll defer to anyone else with better info, but I'd have thought even 50 mm is skimping it.

    Was this not worked out on your BER OP ?

    No, it's not in my BER. Anyone else out there like to share what they used?


  • #10
    The_Bullman
    Registered Users, Registered Users 2 Posts: 1,997 ✭✭✭The_Bullman


    galwaytt wrote: »
    Conflicting - lol. It's just physics.

    But remember why the ff slabs are called 'hollow core' -it's because they are hollow (sic) and are open to the cavity (think heat path/airtightness - or the lack thereof). Remember they're on the walls (think thermal bridging). And finally, even if they were none of those things, why would you want to bury €€€€ in heating a structural part of the building, when you only need to heat the screed.

    At the end of the day though, it's up to you, you'll be paying for the fuel.

    Wouldn't wrapping the slab deal with the airtightness issue?
    If the slab sits on the walls, and is externally or cavity insulated - would there be a thermal bridge?

    It also wasn't mentioned on my BER. Not sure where on the BER its even an option to mention it.

    I don't want to be paying for extra fuel either!


  • #11
    Calahonda52
    Registered Users, Registered Users 2 Posts: 13,365 ✭✭✭✭Calahonda52


    If insulation is used, does the screed not have to be thicker to be more rigid?

    Not insulating it will make temp control in bedrooms much harder as noted.

    the screed should be insulated from the perimeter like downstairs.

    Personally, I wouldn't use UFH upstairs.
    Neither would I use HC slab, but there you be :)

    I would spend the mula on air-tightness and insulation

    “I can’t pay my staff or mortgage with instagram likes”.



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  • #12
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,784 ✭✭✭✭galwaytt


    BarneyMc wrote: »
    No, it's not in my BER. Anyone else out there like to share what they used?

    .. then there's something remiss with your BER then. ..

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #13
    gooseygander
    Registered Users, Registered Users 2 Posts: 317 ✭✭gooseygander


    BarneyMc wrote: »
    No, it's not in my BER. Anyone else out there like to share what they used?
    I went with just 1 inch under screed, also butted up the insulation around the perimeter of all upstairs walls to give screed a bit of room to contract and prevent cracking


  • #14
    sydthebeat
    Subscribers Posts: 43,045 ✭✭✭✭sydthebeat


    galwaytt wrote: »
    .. then there's something remiss with your BER then. ..

    No theres not.

    The BER assumes no heat loss here therefore It doesn't come into the equation.


  • #15
    BarneyMc
    Registered Users, Registered Users 2 Posts: 1,504 ✭✭✭BarneyMc


    sydthebeat wrote: »
    No theres not.

    The BER assumes no heat loss here therefore It doesn't come into the equation.

    Exactly my thoughts! The slab sits within the insulation layer so should have no impact on the overall heating demand. CONTROL of how upstairs is heated is another issue and that's what we're talking about here.


  • #16
    ferryman35
    Registered Users, Registered Users 2 Posts: 85 ✭✭ferryman35


    FWIW we're planning on a 75mm sand cement screed over 50mm on insulation on the first floor, (with upstands around the perimeters)


  • #17
    rampantbunny
    Registered Users, Registered Users 2 Posts: 907 ✭✭✭rampantbunny


    BarneyMc wrote: »
    No, it's not in my BER. Anyone else out there like to share what they used?

    Mine is called out as 30mm insulation/70mm screed.
    I'm actually going 40mm insulation and 60 screed. I was buying 40mm thick board for elsewhere so it made sense to try and get more of the one thickness instead of having lots of differing thicknesses to work with.
    Will use 40mm for edge insulation also.


  • #18
    mfceiling
    Registered Users, Registered Users 2 Posts: 12,999 ✭✭✭✭mfceiling


    It's an interesting topic for me.

    I'm often asked if the underside of the hollowcore should be insulated before I install the ceiling? Or should rockwool be rolled out above the ceiling grid? Or should an insulated board go on the underside of the ceiling?

    My answer - I don't know!!

    If someone can give me a good answer i'll be able to look them confidently in the eye and think "boardsies have my back here"


  • #19
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,784 ✭✭✭✭galwaytt


    sydthebeat wrote: »
    No theres not.

    The BER assumes no heat loss here therefore It doesn't come into the equation.

    ...so a hollowcore slab on a cold exterior wall, or on a interior wall not insulated from the ground is not considered in the BER calculation ?? That doesn't make sense.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #20
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,784 ✭✭✭✭galwaytt


    mfceiling wrote: »
    It's an interesting topic for me.

    I'm often asked if the underside of the hollowcore should be insulated before I install the ceiling? Or should rockwool be rolled out above the ceiling grid? Or should an insulated board go on the underside of the ceiling?

    My answer - I don't know!!

    If someone can give me a good answer i'll be able to look them confidently in the eye and think "boardsies have my back here"

    ...ignoring any issues of bridging or airtightness, the question is why waste energy into the slab above you ?

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #21
    sydthebeat
    Subscribers Posts: 43,045 ✭✭✭✭sydthebeat


    galwaytt wrote: »
    ...so a hollowcore slab on a cold exterior wall, or on a interior wall not insulated from the ground is not considered in the BER calculation ?? That doesn't make sense.

    if it breaks the insulation envelope, then yes technically the acceptable details thermal bridge factor of 0.08 shouldnt be applied.

    But that would just be bad design to allow it to do that, and i have never seen a case where that happened.


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  • #22
    BarneyMc
    Registered Users, Registered Users 2 Posts: 1,504 ✭✭✭BarneyMc


    galwaytt wrote: »
    ...ignoring any issues of bridging or airtightness, the question is why waste energy into the slab above you ?

    Is it 'wasted' or 'thermally stored'?


  • #23
    Strolling Bones
    Registered Users, Registered Users 2 Posts: 615 ✭✭✭Strolling Bones


    wasted


  • #24
    ferryman35
    Registered Users, Registered Users 2 Posts: 85 ✭✭ferryman35


    Would you not think its 'thermally stored'?

    The hollow core slab is resting on the inner leaf of the external wall....so apart from the insulation factor provided by the airtightness membrane which is probably negligible in this case, the hollowcore is already thermally connected to the wall, and is there not going to be some thermal balancing going to be happening there anyway.

    On the other hand - if you insulate the slab underneath and above are you not creating an interstitial situation again.

    Remember that the ff screed is insulated from the walls by the upstands (in addition to them providing an expansion zone) as well as from the hollow core below by the insulation beneath.

    And I guess detail is further improved by using quinnlites to break the thermal bridges between the internal wall leaf and external elements.


  • #25
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    What is all the talk about thermal bridging? Is the thickness of cavity insulation not the same at the floor slab as it is elsewhere in the cavity ? is the question not just about heat delivery only?


  • #26
    BarneyMc
    Registered Users, Registered Users 2 Posts: 1,504 ✭✭✭BarneyMc


    BryanF wrote: »
    What is all the talk about thermal bridging? Is the thickness of cavity insulation not the same at the floor slab as it is elsewhere in the cavity ? is the question not just about heat delivery only?

    It should be.


  • #27
    sydthebeat
    Subscribers Posts: 43,045 ✭✭✭✭sydthebeat


    it is, its simply a responsiveness issue.


    i would spec around 50mm, depending on depths to play with.

    theres really no point going any thicker because the delta T will be quite small between the two, so heat flux will be slow.


  • #28
    Rabbo
    Registered Users, Registered Users 2 Posts: 637 ✭✭✭Rabbo


    sydthebeat wrote: »
    No theres not.

    The BER assumes no heat loss here therefore It doesn't come into the equation.

    It dosen't effect the heat loss but it will effect the responsiveness category and therefore effect the BER.

    There are plenty of horror stories out there of almost unusable underfloor heating systems because there were installed in thick concrete slabs. Installing in a screed on a concrete first floor with no insulation in between amounts to the same thing. It would take hours for the heat to penetrate all that concrete.


  • #29
    sydthebeat
    Subscribers Posts: 43,045 ✭✭✭✭sydthebeat


    Rabbo wrote: »
    It dosen't effect the heat loss but it will effect the responsiveness category and therefore effect the BER.

    There are plenty of horror stories out there of almost unusable underfloor heating systems because there were installed in thick concrete slabs. Installing in a screed on a concrete first floor with no insulation in between amounts to the same thing. It would take hours for the heat to penetrate all that concrete.

    it wont effect the BER.

    none of the responsiveness catagories are applicable to this situation.

    if you have the typical "UFH in screed above insulation" in the ground floor, you would be incorrect to input any other responsiveness category, in my opinion of course ;)

    "underfloor heating, pipes in concrete slab" is not a correct input in this situation.


  • #30
    Rabbo
    Registered Users, Registered Users 2 Posts: 637 ✭✭✭Rabbo


    True, you would definitely have a reasonable argument in the case of an SEAI audit, especially if the main living room was on the ground floor.

    However from the homeowners point of view, I definitely wouldn't recommend that detail.


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  • #31
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,784 ✭✭✭✭galwaytt


    sydthebeat wrote: »
    it wont effect the BER.

    none of the responsiveness catagories are applicable to this situation.

    if you have the typical "UFH in screed above insulation" in the ground floor, you would be incorrect to input any other responsiveness category, in my opinion of course ;)

    "underfloor heating, pipes in concrete slab" is not a correct input in this situation.

    ...going back to OP's original query though, it most certainly would. The screed needs to be insulated from the slab & walls.

    Even my own house, an engineered timber joist and deck to FF, I insulated the screed and in a timber build it's in a 'better' environment to begin with.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



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