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Wide cavity vs ewi

  • 30-04-2019 8:26pm
    #1
    Registered Users Posts: 95 ✭✭


    Hi all,

    We are just planning out our self build and are between either block on flat with ewi or a wide cavity (either full fill bead or partial fill board). At the moment I'm leaning towards the ewi as it seems like a better end product from a thermal conductivity point of view however as the site is quite exposed I'm nervous about the durability. I'm just wondering what people's opinions of the pros/cons are?

    Thanks all


Comments

  • Moderators, Home & Garden Moderators Posts: 10,135 Mod ✭✭✭✭BryanF


    Have read the ten plus years of very detailed threads on this topic?


  • Registered Users Posts: 12,141 ✭✭✭✭Calahonda52


    Jcanty85 wrote: »
    Hi all,

    We are just planning out our self build and are between either block on flat with ewi or a wide cavity (either full fill bead or partial fill board). At the moment I'm leaning towards the ewi as it seems like a better end product from a thermal conductivity point of view however as the site is quite exposed I'm nervous about the durability. I'm just wondering what people's opinions of the pros/cons are?

    Thanks all

    You can't really look at this in isolation to the rest of the build.

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



  • Registered Users Posts: 95 ✭✭Jcanty85


    I've been through every board here but I still have not arrived at a clear winner. I appreciate it can't be taken in isolation however as a starting point I thought it would be a good start. Hoping to get U value under 0.12 but in order to get this with wide cavity/Eco bead or similar I'd have to nearly go to 300mm. This will naturally throw up a lot of issues from a detail PoV so I was wondering if a 6 inch pumped cavity with (budget allowing) 4-5 inches of ewi but a better option or what people's opinion on this would be?


  • Moderators, Home & Garden Moderators Posts: 10,135 Mod ✭✭✭✭BryanF


    Go with ewi or cavity insulation

    Why are you aiming for .12w/m2k ?
    Passive standard is .15
    Have done phpp calc ?
    Sorting out thermal bridging or better glazing, may be a better spend


  • Registered Users Posts: 95 ✭✭Jcanty85


    BryanF wrote: »
    Go with ewi or cavity insulation

    Why are you aiming for .12w/m2k ?
    Passive standard is .15
    Have done phpp calc ?
    Sorting out thermal bridging or better glazing, may be a better spend

    Yeah you're right, .12 was a bit unrealistic, was just my attempt at future proofing. A 200mm wide pumped cavity gets us to .15 so maybe the extra money would be better spent elsewhere.


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  • Subscribers Posts: 40,735 ✭✭✭✭sydthebeat


    Jcanty85 wrote: »
    Yeah you're right, .12 was a bit unrealistic, was just my attempt at future proofing. A 200mm wide pumped cavity gets us to .15 so maybe the extra money would be better spent elsewhere.

    100% correct.

    Insulation really suffered the law of diminishing returns at these levels.

    Look at resolving thermal bridges instead


  • Registered Users Posts: 1,166 ✭✭✭Still waters


    block on flat with Ewi all the way


  • Moderators, Home & Garden Moderators Posts: 10,135 Mod ✭✭✭✭BryanF


    block on flat with Ewi all the way

    Why?


  • Registered Users Posts: 95 ✭✭Jcanty85


    Think the full fill wide cavity will be the way forward. Solid wall inside/out plus a good bit saved on the cost of rendering. Following on from this what are people's opinions on the thermal foundation blocks from a thermal PoV. It might be old fashioned but as my site is suitable to strip foundations I am hesitant to opt for insulated raft due to weight issues (blockwork/hollowcore slab). Hoping to only need two blocks on flat plus a block on edge so I was thinking of rolling a sheet of plastic out over the compacted fill (will not be much), then building two thermal blocks on flat and one on edge. 300 eps under floor. Dpc/radon under insulation and over block on edge. Additional bottom poly is only intended to keep thermal blocks from getting damp (site is sloping but just in case). I know structural advice is not permitted but any opinions on thermal bridging is appreciated. Thanks in advance.


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