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Cavity Wall Insulation (with no greater than 150mm cavity)

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  • 17-07-2014 6:16pm
    #1
    Bubbling
    Registered Users Posts: 52 ✭✭


    New thread covering an often discussed topic:

    Kingspan have today quoted me a u value of 0.17 W/m2K for

    - 3mm skim gypsum plaster,
    - 10mm sand and cement plaster,
    - 100mm thick 5N/Sqmm concrete block,
    - 100mm Kooltherm K8 Cavity Wall Insulation,
    - 40mm Residual cavity (140mm cavity in total)
    - 100mm thick 5N/Sqmm concrete block,
    - 20mm sand and cement render.

    This is well within the Part L threshold of 0.21 W/m2K and is within the 150mm max cavity width that is structurally advised. This seems to tick all the boxes as far as I can see?

    Or am I missing something?

    As this is such a straight forward construction, why then is a dry lining board often specified in addition to having cavity wall insulation in similar construction?

    Thanks!


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    #2
    sydthebeat
    Subscribers Posts: 41,062 ✭✭✭✭sydthebeat


    Did you price that up yet against construction that offer a similar u value?

    If you do, you might see why larger cavities with pumped insulation is more commonly used ;)


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    #3
    antiskeptic
    Registered Users Posts: 9,555 ✭✭✭antiskeptic


    Bubbling wrote: »
    - 100mm Kooltherm K8 Cavity Wall Insulation

    Presumably installed on a billiard table-flat wall with zero gaps anywhere. I wonder that the pragmatic reality is (as a % of the perfect installation)?


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    #4
    Bubbling
    Registered Users Posts: 52 ✭✭Bubbling


    antiskeptic wrote: »
    Presumably installed on a billiard table-flat wall with zero gaps anywhere. I wonder that the pragmatic reality is (as a % of the perfect installation)?

    But it would seem there is likely "weak" point with retro fit cavity fill from a technical view point. It is difficult to inspect the job on completion and there are likely cold spots at step docs, wall penetrations, etc.

    At least with with installing a cavity insulation board, it can be inspected during the construction....


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    #5
    hexosan
    Registered Users Posts: 1,735 ✭✭✭hexosan


    Bubbling wrote: »
    But it would seem there is likely "weak" point with retro fit cavity fill from a technical view point. It is difficult to inspect the job on completion and there are likely cold spots at step docs, wall penetrations, etc.

    At least with with installing a cavity insulation board, it can be inspected during the construction....

    How do you plan on inspecting every single board that the block layer fits.


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    #6
    Bubbling
    Registered Users Posts: 52 ✭✭Bubbling


    hexosan wrote: »
    How do you plan on inspecting every single board that the block layer fits.

    It wouldn't be possible to inspect them all. But at least a percentage can be checked as work progresses.

    I'm just throwing open the argument of one system versus the other to try to decide which offers the highest quality finished product, a good u-value and using a 150mm maximum cavity.


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    #7
    beyondpassive
    Registered Users Posts: 558 ✭✭✭beyondpassive


    Bubbling wrote: »
    This is well within the Part L threshold of 0.21 W/m2K and is within the 150mm max cavity width that is structurally advised.

    0.21 is the backstop, you need about 0.18 to neet the EPC in DEAP. I's look at 120mm PIR in a 160 cavity or full fill 250m cavity.


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    #8
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,140 Mod ✭✭✭✭BryanF


    Bubbling wrote: »
    But it would seem there is likely "weak" point with retro fit cavity fill from a technical view point. It is difficult to inspect the job on completion and there are likely cold spots at step docs, wall penetrations, etc.

    At least with with installing a cavity insulation board, it can be inspected during the construction....
    • the weak point is the insulation boards not installed correctly.as has been the case for years: thermal looping in the cavity, insulation board not cut correctly, not fitting correctly, not sealed together, snots in the cavity stopping the above happening & its impossible to check this.
    • when you pump the beads in, its done under pressure and there is an option to use thermal imagining to ensure continuity afterwards.
    Bubbling wrote: »
    1. Kingspan have today quoted me a u value of 0.17 W/m2K for
    2. well within the Part L threshold of 0.21 W/m2K
    3. and is within the 150mm max cavity width that is structurally advised.
    4. This seems to tick all the boxes as far as I can see? Or am I missing something?
    5. As this is such a straight forward construction, why then is a dry lining board often specified in addition to having cavity wall insulation in similar construction?

    1. quoted by a manufacturer that have been known to use unrealistic values. your BER/Arch will review the certs and decide if this is correct
    2. no its not, as highlighted by others. its no longer acceptable to use elemental u-values. your BER/Arch should be specifying the U-value as part of the overall buildings heat loss calc. walls are an easy place to increase the average U-value to balance other areas where U-values are not so readily achieved
    3. lazy
    4. yes your arch/BER review of this
    5. why is drylining specified in new builds? laziness and lack of knowledge of building physics. keeping the insulation in the one place is best. drylining increases thermal bridging issues.


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    #9
    DeeJunFan
    Registered Users Posts: 110 ✭✭DeeJunFan


    beyondpassive wrote: »
    0.21 is the backstop, you need about 0.18 to neet the EPC in DEAP. I's look at 120mm PIR in a 160 cavity or full fill 250m cavity.

    A 250 mm Full fill cavity give a U-value of 0.12

    I'm thinking of going for a 175mm cavity full fill which will give me a u-value of 0.17

    Do you think the 0.05 in difference is economically beneficial or more a good to have?


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    #10
    DeeJunFan
    Registered Users Posts: 110 ✭✭DeeJunFan


    Bubbling wrote: »
    New thread covering an often discussed topic:

    Kingspan have today quoted me a u value of 0.17 W/m2K for

    - 3mm skim gypsum plaster,
    - 10mm sand and cement plaster,
    - 100mm thick 5N/Sqmm concrete block,
    - 100mm Kooltherm K8 Cavity Wall Insulation,
    - 40mm Residual cavity (140mm cavity in total)
    - 100mm thick 5N/Sqmm concrete block,
    - 20mm sand and cement render.

    This is well within the Part L threshold of 0.21 W/m2K and is within the 150mm max cavity width that is structurally advised. This seems to tick all the boxes as far as I can see?

    Or am I missing something?

    As this is such a straight forward construction, why then is a dry lining board often specified in addition to having cavity wall insulation in similar construction?

    Thanks!

    When i put similar wall build up into u-value calculator i'm getting 0.207 so you could be very boarderline.


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    #11
    Drift
    Closed Accounts Posts: 1,395 ✭✭✭Drift


    What are people's experiences with the structural engineering aspects of walls with cavities in excess of 150mm?

    There seems to be precious little guidance in Eurocode 6 regarding at what point a wall ceases to be a cavity wall and becomes two separate 100mm walls.

    SR325 refers to wall ties for cavities above 150mm requiring specialist design but to be honest where you're getting beyond the designs that EC6 covers you're talking VERY specialist!


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    #12
    BarneyMc
    Registered Users Posts: 1,504 ✭✭✭BarneyMc


    Drift wrote: »
    What are people's experiences with the structural engineering aspects of walls with cavities in excess of 150mm?

    There seems to be precious little guidance in Eurocode 6 regarding at what point a wall ceases to be a cavity wall and becomes two separate 100mm walls.

    SR325 refers to wall ties for cavities above 150mm requiring specialist design but to be honest where you're getting beyond the designs that EC6 covers you're talking VERY specialist!

    I think you'll need to keep away from asking structural questions here. All I'll say is your structural engineer will have to be happy with it.


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    #13
    Drift
    Closed Accounts Posts: 1,395 ✭✭✭Drift


    BarneyMc wrote: »
    I think you'll need to keep away from asking structural questions here. All I'll say is your structural engineer will have to be happy with it.

    I am a structural engineer BarneyMc and I'm not happy with it! ;)

    As you said structural advice is not allowed here but I don't see any reason why people can't say that their engineer is or is not happy with it. I get the feeling (although I may be wrong) that in a lot of buildings (houses particularly) that have cavities in the 200+mm range the walls have not been subject to a specialist structural design as they should.

    In general terms:

    Lateral loading on cavity walls (wind loads, suction, etc.) can only be split between the two leaves if the wall ties are such that they ensure the leaves act as one unit and for wall ties over 150mm that needs specialist wall tie design - which is getting super specific!

    And when it comes to vertical loads on walls with very wide cavities there just doesn't seem to be much guidance either way!

    There may be some guidance out there that I'm missing though.


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    #14
    BarneyMc
    Registered Users Posts: 1,504 ✭✭✭BarneyMc


    My engineer was happy with it, if not I assume he would not be signing off. I hope anyway!


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    #15
    Drift
    Closed Accounts Posts: 1,395 ✭✭✭Drift


    We're a conservative bunch - I'm sure he wouldn't sign off unless he were happy.

    The question is what evidence or calculations did he need/do to make himself happy with the 200mm cavity.


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    #16
    chrysagon
    Registered Users Posts: 2,813 ✭✭✭chrysagon


    Pumping in the beads not possibly transfer damp?


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    #17
    4Sticks
    Registered Users Posts: 1,155 ✭✭✭4Sticks


    Drift wrote: »
    There may be some guidance out there that I'm missing though.

    BS 5268 suite of documents published 2005.


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    #18
    Drift
    Closed Accounts Posts: 1,395 ✭✭✭Drift


    4Sticks wrote: »
    BS 5268 suite of documents published 2005.

    It's actually 5628 and has been superseded by Eurocode 6. (IS EN 1996)

    Although still very informative for background reading.


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    #19
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,140 Mod ✭✭✭✭BryanF


    chrysagon wrote: »
    Pumping in the beads not possibly transfer damp?
    pumping bead is now standard practice


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    #20
    Drift
    Closed Accounts Posts: 1,395 ✭✭✭Drift


    Just had a look at my old BS5628 and 4Sticks is correct it discusses cavities up to 300mm in width. One still cannot use the tables in BS5628 to size wall panels in walls with large cavities. You have to do a bespoke design for each wall but at least that code allows you to do this.

    Leads to an interesting query as to whether you can use an out of date code (from the UK) instead of IS EN 1996. If the client agrees to same in writing would it be ok?

    Or can you use the wall tie requirements from BS5628 and then carry out the loading and resistance calculations in line with IS EN 1996? A hybrid sort of system.

    I'm just throwing these queries out there btw, I'm not saying I have the answers!


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    #21
    4Sticks
    Registered Users Posts: 1,155 ✭✭✭4Sticks


    This document at a quick glance appears to regurgitate a lot of the BS 5628 content - including wide cavities.


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    #22
    Drift
    Closed Accounts Posts: 1,395 ✭✭✭Drift


    4Sticks wrote: »
    This document at a quick glance appears to regurgitate a lot of the BS 5628 content - including wide cavities.

    I haven't seen that lad before. I'll take a look later.

    It looks like it might be the BSi equivalent of NSAI SR 325.


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