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Cavity Insulation- is 150mm enough please help

  • 28-08-2014 1:17am
    #1
    blondie29
    Registered Users Posts: 103 ✭✭


    Hi guys/girls

    Hoping to start our self build in next few weeks..building a 2800sq foot storey and half. We are planning on installing UFH more than likely powered by geothermal HP.

    We have a provisional BER reading of A3 from the following spec:

    - Floor: 100mm floor insulation
    - Walls: 150mm cavity with platinum bead
    - Roof: 150mm king span foil backed insulation between rafters with 50 mm foil backed slab on surface of slopes. 300mm rolled insulation on flat roof sections.

    I am just curious to see if the 150mm pumped cavity is enough as we are hearing conflicting stories about people dry lining walls etc but then walls not being able to breath properly. Our architect seems to think 150mm pumped cavity is enough.

    Can someone explain in simple language, still learning the whole building side of things!

    We would really like to do this properly while we are at it (obviously a budget in mind) & have the closest thing to an airtight" house as possible.

    We were going to put in HRV but don't think budget can stretch that far, we are having vents in windows that can open/close.

    Any help is much appreciated.


Comments

  • #2
    893bet
    Registered Users Posts: 8,727 ✭✭✭893bet


    Do a provsisinal BER and it will tell you if 150 is enough.

    An airtight house with vents in the walls. Think about the logic there. You must put in the hrv system.


  • #3
    DeeJunFan
    Registered Users Posts: 110 ✭✭DeeJunFan


    blondie29 wrote: »
    Hi guys/girls

    Hoping to start our self build in next few weeks..building a 2800sq foot storey and half. We are planning on installing UFH more than likely powered by geothermal HP.

    We have a provisional BER reading of A3 from the following spec:

    - Floor: 100mm floor insulation
    - Walls: 150mm cavity with platinum bead
    - Roof: 150mm king span foil backed insulation between rafters with 50 mm foil backed slab on surface of slopes. 300mm rolled insulation on flat roof sections.

    I am just curious to see if the 150mm pumped cavity is enough as we are hearing conflicting stories about people dry lining walls etc but then walls not being able to breath properly. Our architect seems to think 150mm pumped cavity is enough.

    Can someone explain in simple language, still learning the whole building side of things!

    We would really like to do this properly while we are at it (obviously a budget in mind) & have the closest thing to an airtight" house as possible.

    We were going to put in HRV but don't think budget can stretch that far, we are having vents in windows that can open/close.

    Any help is much appreciated.

    Seems like you have a provisional BER.

    To be honest if you are going with UFH i would use more than 100mm of insulation in the floor.

    If you are going for an airtight house (what target is set for air-tightness?) you are going to want MHRV.

    Why spend money making it air-tight and then cut holes in the windows to let lots of cold air in?


  • #4
    BarneyMc
    Registered Users Posts: 1,504 ✭✭✭BarneyMc


    What U values are you getting for your floor, walls, roof, etc. with the proposed levels of insulation?


  • #5
    galwaytt
    Registered Users Posts: 12,751 ✭✭✭✭galwaytt


    blondie29 wrote: »
    Hi guys/girls

    Hoping to start our self build in next few weeks..building a 2800sq foot storey and half. We are planning on installing UFH more than likely powered by geothermal HP.

    We have a provisional BER reading of A3 from the following spec:

    - Floor: 100mm floor insulation
    - Walls: 150mm cavity with platinum bead
    - Roof: 150mm king span foil backed insulation between rafters with 50 mm foil backed slab on surface of slopes. 300mm rolled insulation on flat roof sections.

    I am just curious to see if the 150mm pumped cavity is enough as we are hearing conflicting stories about people dry lining walls etc but then walls not being able to breath properly. Our architect seems to think 150mm pumped cavity is enough.

    Can someone explain in simple language, still learning the whole building side of things!

    We would really like to do this properly while we are at it (obviously a budget in mind) & have the closest thing to an airtight" house as possible.

    We were going to put in HRV but don't think budget can stretch that far, we are having vents in windows that can open/close.

    Any help is much appreciated.


    No HRV = not airtight imho. And if you're using GSHP you'll need to be reaching for good airtightness.

    That is not enough insulation for UFH -doesn't even meet regs.

    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” 



  • #6
    shell820810
    Registered Users Posts: 50 ✭✭shell820810


    150mm of beads will get you a u value of *about* 0.19 or 0.20. If you could even increase the cavity to 175mm you could improve u value to 0.16 or 0.17. Alternatively, a kingspan 110mm board in the 150mm cavity will get you 0.15 or 0.16 u value, but is much more expensive.

    Eg for comparison in the north, I was quoted £8 sq meter for platinum bonded bead in 175mm cavity, whereas kingspan 110mm board is about £21 per square metre, for virtually the same u value. The u value of the board is also only accurate if the board is fitted perfectly, which will also come at an additional cost of the extra time it takes the builder to do this.


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  • #7
    shell820810
    Registered Users Posts: 50 ✭✭shell820810


    150mm of beads will get you a u value of *about* 0.19 or 0.20. If you could even increase the cavity to 175mm you could improve u value to 0.16 or 0.17. Alternatively, a kingspan 110mm board in the 150mm cavity will get you 0.15 or 0.16 u value, but is much more expensive.

    Eg for comparison in the north, I was quoted £8 sq meter for platinum bonded bead in 175mm cavity, whereas kingspan 110mm board is about £21 per square metre, for virtually the same u value. The u value of the board is also only accurate if the board is fitted perfectly, which will also come at an additional cost of the extra time it takes the builder to do this.

    Just a rough idea from kingspan info

    A1 rating, 2 euro per sq metre to heat
    A2 rating, 3 euro per sq metre to heat
    A3 rating, 5 euro per sq metre to heat

    difference in 0.16 to 0.20 is roughly A2 to A3, quite significant savings.


  • #8
    sydthebeat
    Subscribers Posts: 40,953 ✭✭✭✭sydthebeat


    shell820810 wrote: »

    Just a rough idea from kingspan info

    A1 rating, 2 euro per sq metre to heat
    A2 rating, 3 euro per sq metre to heat
    A3 rating, 5 euro per sq metre to heat

    difference in 0.16 to 0.20 is roughly A2 to A3, quite significant savings.

    forgive my bluntness buts thats complete bollix from kingspan and only a way for them to sell more expensive products.

    The DEAP assessment has way too many illogical conventions and assumptions for it to be considered any useful kind of cost comparison software.

    what i would say to the OP is that
    1. yes 150 platinum bead is generally the minimum acceptable to give a wall u value of less than 0.2
    2. 100 floor insulation generally doesnt meet the 0.16 u value required for UFH
    3. those values look to be in the borderline or compliance / non compliance. your assessor should be saying exactly what product hes including in the assessment as there are significant costs differences between products ie of hes including kingspan kooltherm (phenolic foan) or xtratherm (polyisocyranuate foam)


  • #9
    shell820810
    Registered Users Posts: 50 ✭✭shell820810


    sydthebeat wrote: »
    forgive my bluntness buts thats complete bollix from kingspan and only a way for them to sell more expensive products.

    The DEAP assessment has way too many illogical conventions and assumptions for it to be considered any useful kind of cost comparison software.

    what i would say to the OP is that
    1. yes 150 platinum bead is generally the minimum acceptable to give a wall u value of less than 0.2
    2. 100 floor insulation generally doesnt meet the 0.16 u value required for UFH
    3. those values look to be in the borderline or compliance / non compliance. your assessor should be saying exactly what product hes including in the assessment as there are significant costs differences between products ie of hes including kingspan kooltherm (phenolic foan) or xtratherm (polyisocyranuate foam)

    Are you able to give any sort of indication of cost savings between ratings?


  • #10
    sydthebeat
    Subscribers Posts: 40,953 ✭✭✭✭sydthebeat


    shell820810 wrote: »
    Are you able to give any sort of indication of cost savings between ratings?

    a certified passive house in carlow which is heated by means of an electric element in its HRV system is rated as B2

    yet its heating bills would be in the very low €100s per annum

    as i said above....
    the ratings cannot be used for cost comparisons as DEAP has way too many illogical conventions and assumptions for it to be considered any useful kind of cost comparison software.


  • #11
    shell820810
    Registered Users Posts: 50 ✭✭shell820810


    sydthebeat wrote: »
    a certified passive house in carlow which is heated by means of an electric element in its HRV system is rated as B2

    yet its heating bills would be in the very low €100s per annum

    as i said above....
    the ratings cannot be used for cost comparisons as DEAP has way too many illogical conventions and assumptions for it to be considered any useful kind of cost comparison software.

    fair enough, energy assessment is different here in the north, we dont have to have a renewable source etc

    Put the question another way, is there a rough estimate of the savings of increasing insulation from A3 (about 0.19) to A2 (about 0.16), or is this too general again? Assuming airtightness is same level at both, same method of heating etc.


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  • #12
    sydthebeat
    Subscribers Posts: 40,953 ✭✭✭✭sydthebeat


    first, just a correction, they were B1 rated... just checked.

    the DEAP software in its first incarnation (2007) used to have a cost comparison feature, but this was quickly removed by SEAI. they never officially came clean as to why they removed it, but its because it gave completely unrealistic figures.

    what you really need is a phpp assessment, that is specific to your house and your use. DEAP isnt anywhere near specific as phpp.

    so i suppose what im saying is that DEAP isnt suitable to use for cost comparisons... and what kingspan say is a sales pitch, which is their want.


  • #13
    blondie29
    Registered Users Posts: 103 ✭✭blondie29


    Hi OP here

    Sorry posted wrong floor insulation ours is actually 150mm not 100mm as originally posted.

    We got provisional BER reading of A3.

    We visited a house who have the same spec as ours with Geo UFH & have future proof windows with small vents on the top of the windows. We thought we could get around not the HRV with those.

    We are still looking into HRV systems, there seems to be a lot of maintenance with them also. Has anybody got any recommendations? We live in Northwest.

    As regards the 150mm pumped cavity, is that enough? Do people have bigger cavity's?

    Thanks


  • #14
    blondie29
    Registered Users Posts: 103 ✭✭blondie29


    Also how do you calculate the U values?


  • #15
    shell820810
    Registered Users Posts: 50 ✭✭shell820810


    blondie29 wrote: »
    Hi OP here

    Sorry posted wrong floor insulation ours is actually 150mm not 100mm as originally posted.

    We got provisional BER reading of A3.

    We visited a house who have the same spec as ours with Geo UFH & have future proof windows with small vents on the top of the windows. We thought we could get around not the HRV with those.

    We are still looking into HRV systems, there seems to be a lot of maintenance with them also. Has anybody got any recommendations? We live in Northwest.

    As regards the 150mm pumped cavity, is that enough? Do people have bigger cavity's?

    Thanks

    Depends on what your target is.
    150mm is enough to get you to A3. Everyone I have spoken to says to put the cavity as wide as you can. I was originally aiming for 250mm. But we had issues with building control in the north with anything over 200mm so we are going with 175mm now, and taking a hit on the u value.

    Most of the manufacturers will give you u values for their products, which is based on a certain build spec. There is software online that allows you to calculate your own if you want to go down that route.


  • #16
    RITwing
    Banned (with Prison Access) Posts: 246 ✭✭RITwing


    shell820810 wrote: »
    150mm is enough to get you to A3.

    No one measure by itself will "get you to A3".


  • #17
    hexosan
    Registered Users Posts: 1,735 ✭✭✭hexosan


    I've a 250mm cavity if I was going again id of done a 200mm cavity. You get hassle with longer wall straps, had problems getting Steelite lintels, closing cavity at wall plate with the engineer.


  • #18
    rockabaloo
    Registered Users Posts: 103 ✭✭rockabaloo


    150mm is fine (in the greater scheme of things because some things in life are more important than a U-value printed on paper).

    http://www.boards.ie/vbulletin/showthread.php?p=81829386

    Do the maths. Saving the world would be nice but you've gotta look after your finances and your family too.

    You'd be better sticking a jumper on for a couple of days a year rather than chasing some U-value pipe dream.


  • #19
    galwaytt
    Registered Users Posts: 12,751 ✭✭✭✭galwaytt


    sydthebeat wrote: »
    a certified passive house in carlow which is heated by means of an electric element in its HRV system is rated as B2

    yet its heating bills would be in the very low €100s per annum

    as i said above....
    the ratings cannot be used for cost comparisons as DEAP has way too many illogical conventions and assumptions for it to be considered any useful kind of cost comparison software.

    Exactly, which further serves to undermine the relevance of BER in the sales market (reference other thread on this).

    The first PHI certified house in Ireland is 10yrs old this year, and under current regs is only a C-something iirc.

    Goes to show the complete irrelevance of throwing letters/numbers out there.

    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
    blondie29
    Registered Users Posts: 103 ✭✭blondie29


    Thanks for some of the replies, I'm still none the wiser!

    Has anyone pumped cavity 150mm & dry lined also? We are hoping the 150mm pumped cavity will be enough.

    With regards to anyone with HRV, I see that you have to clean filters couple times a year, are they expensive to replace? Also I'm sure there are hard to access places with them eg ducts etc am I right in saying they need to be serviced once a year too?


  • #21
    hexosan
    Registered Users Posts: 1,735 ✭✭✭hexosan


    Avoid with a barge pole anyone who suggests drylining a new build. It's madness


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  • #22
    sydthebeat
    Subscribers Posts: 40,953 ✭✭✭✭sydthebeat


    galwaytt wrote: »
    Exactly, which further serves to undermine the relevance of BER in the sales market (reference other thread on this).

    The first PHI certified house in Ireland is 10yrs old this year, and under current regs is only a C-something iirc.

    Goes to show the complete irrelevance of throwing letters/numbers out there.

    Your still assuming a use for it which it isn't designed.

    It's simply a rating procedure used to compare similar buildings from an energy use point of view.

    Its not a heat loss survey
    It's not an energy costing tool
    It's not a energy use assessment specific to the dwelling and its users.

    Its a tool use to compare, pure and simple.


  • #23
    dfader
    Registered Users Posts: 120 ✭✭dfader


    blondie29 wrote: »
    We were going to put in HRV but don't think budget can stretch that far, we are having vents in windows that can open/close.
    If you cannot afford hrv then maybe you should consider downsizing your house. Drop 400 sq ft and you could save e40000. A decent architect would maximise use of space. 2400 sqft is still a large house. You wouldn't miss it. Better of in a smaller higher spec and more efficient house.
    Airtightness without hrv is madness as is drylining in new builds especially when using underfloor heating. 100mm ins in floor is not enough with underfloor heating.


  • #24
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,140 Mod ✭✭✭✭BryanF


    rockabaloo wrote: »
    150mm is fine (in the greater scheme of things because some things in life are more important than a U-value printed on paper).

    http://www.boards.ie/vbulletin/showthread.php?p=81829386

    Do the maths. Saving the world would be nice but you've gotta look after your finances and your family too.

    You'd be better sticking a jumper on for a couple of days a year rather than chasing some U-value pipe dream.

    Who's maths are you referring to? Not yours I hope?


  • #25
    rockabaloo
    Registered Users Posts: 103 ✭✭rockabaloo


    Yup. Cos it's right and I'm right.

    Gotta do what makes sense in terms of saving money in your own lifetime. It's just being idealistic worrying about how a house will perform 100 years down the line.


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