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New build, What ext wall type to use??

  • 25-01-2013 5:21pm
    #1
    Tim Toolman
    Closed Accounts Posts: 20 ✭


    Just weighing up the pros and cons of different types of wall construction for a friend who is currently at the planning stage. I get differing advice
    (1) that you should pump a 100mm cavity blockwork wall, and then slab the inner leaf with the 50mm thick insulated slab with the plasterboard inbuilt, and if your BER doesn't reach a pass you can increase this thickness to 75mm.
    (2) that you should use 100mm concrete blockwork outer leaf, 150 pumped insulation cavity with a quinnlite internal leaf (i think the thickness for this would be 100mm).
    and (3) that you should build with an outer leaf concrete blockwork wall, 200mm pumped cavity insulation and a 100mm inner leaf concrete blockwork wall.

    These types are within the scope of comprehension at the moment, external insulation is not being considered maybe wrongly, as it does look like the most popular wall type promoted by the PH. Does anyone have any information or experience with the above wall types and what in your opinions are the best build, and which types are easier on the pocket. Thanks in advance for your help.


Comments

  • #2
    heavydawson
    Registered Users, Registered Users 2 Posts: 1,230 ✭✭✭heavydawson


    Hey Tim,
    It's a new build so avoid insulated slabs at all if you can. Too many potential condensation problems if the wall construction+insulation behind the slab is not properly designed WRT the dew point.
    Theres also the issue of thermal mass. Insulated slabs will effectively act as a heat "mirror", which will keep the wall behind it cold and heat the room quicker, but it will also cool quicker when the heat source is turned off.

    having a sand/cement plaster finish on the blocks will allow the concrete to store the heat and release it gradually after the heat source has been switched off. It's worth your while reading up on thermal mass and interstitial condenstion (not as related topics, but individual aspects of the wall construction).

    For me, I think a 4" cavity is too narrow for pumped beads. I think 6" is too narrow too. I'd be looking at a 225mm cavity pumped.
    You seem to be hell-bent on pumping the cavity, so I would spend a little looking at the alternatives. There are solid boards, or more sustainable alternatives such as wood fibre, etc.
    As you mentioned, external wall insulation is another perfectly valid insulation type.

    At a bare minimum, you have to have a wall that meets the building regs as regards u-values, but that's a low bar. You should be aiming to insulate the walls to the best of your ability/budget.

    And I don't mean to be smart, but it looks like you're taking advice for a friend who's looking to you for advice? Your friend should be talking to a heating engineer or arch tech about this sort of thing. Happy to shoot the breeze, but this is a huge part of any build, and should really be handled and detailed by professionals.


  • #3
    Tim Toolman
    Closed Accounts Posts: 20 ✭Tim Toolman


    Posted by Heavy Dawson "And I don't mean to be smart, but it looks like you're taking advice for a friend who's looking to you for advice? Your friend should be talking to a heating engineer or arch tech about this sort of thing. Happy to shoot the breeze, but this is a huge part of any build, and should really be handled and detailed by professionals."

    Yeah I am a arch tech, but have been out of the field for quite a while and am looking to others as to their opinions as there are so numerous the options available now, it takes time to catch up with so many changes. Thanks for your piece.


  • #4
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    Tim Toolman wrote: »
    Yeah I am a arch tech, but have been out of the field for quite a while and am looking to others as to their opinions as there are so numerous the options available now, it takes time to catch up with so many changes. Thanks for your piece.
    I'd recommend studying the BER software, analysing the 2011 TGDL , attending a passive house course, attending an air-tightness course and reading around the topic of hygroscopic issues in dwellings with increased levels of insulation. Welcome back!


  • #5
    heavydawson
    Registered Users, Registered Users 2 Posts: 1,230 ✭✭✭heavydawson


    BryanF wrote: »
    I'd recommend studying the BER software, analysing the 2011 TGDL , attending a passive house course, attending an air-tightness course and reading around the topic of hygroscopic issues in dwellings with increased levels of insulation. Welcome back!

    ^
    | What he said :-)
    Hopefully I didn't cause any offence. It's actually a great time to be building. Aside from the availability of good labour, the amount of genuinely useful information/courses out there is greater than ever before. There's a huge amount of knowledge on sustainable building as well.
    You could spend days reading the various threads here on boards around all of the issues BryanF mentioned. It's well worth it.


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