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Housing - New Build: Insulating a Catnic 'Extreme Load Lintel'

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    We will have a large sliding door across the back of our new build house and the builders have installed a Catnic 'extreme lintel' over the span.

    The smaller catnic lintels that have been used above the windows are thermally broken, but the 'extreme load lintel' don't appear to have any thermal break.

    The face bricks have been built up on the outside wall of the house so we can no longer get to it, and I don't believe they have installed any insulation between the facing bricks / DPC and the face of the lintel. The interior of the lintel is still exposed as per the photo below.

    I'm hoping you can give me some thoughts on what to do now. Taking down the facing brick isn't really an option. Can we add some insulation from the inside? Is there a big condensation risk of doing this and the insulation would just get wet? Any thoughts gratefully received.
      Capture.JPG
  2.  
    Lintel detail from the catnic website. I believe this is the make-up we have (aka no insulation around the lintel)
      Catnic Lintel.JPG
    • CommentAuthortony
    • CommentTimeAug 14th 2015
     
    Wet plastering? Is the cavity filled?
    • CommentAuthorIan1961
    • CommentTimeAug 14th 2015
     
    You could fill the internally exposed web of the lintel with a high-performance board insulation but you'll need a vapour barrier on the warm side of the insulation to stop warm moisture laden air from reaching the cold surface of the steel and condensing.
  5.  
    The external cavity is 150mm wide, with 100mm of Kingspan + 50mm air gap. (This is the make-up above and below the lintel).

    Inside we're having a parge coat for air tightness and then plasterboard on top. I haven't asked the builder the method he'll be using for the plasterboard, but I assume dot and dab.
  6.  
    Should you have a vapour barrier anyway as I assume condensation would be a risk whether not you added some high performance insulation internally?
    • CommentAuthorIan1961
    • CommentTimeAug 14th 2015
     
    If it were my house I'd be tempted to fill in the exposed void of the web of the steel lintel with foil faced insulation board so that the insulation fills the web and is flush with the adjacent blockwork. You then need to fill any small gaps that are left at the edge of the insulation with an expanding foam or something similar to prevent moisture laden warm air getting to the cold surface of the web of the steel lintel. The alternative would be to try and stick a sheet of visqueen type vapour barrier over the face of the insulated lintel - the problem with doing it that way would be getting a decent seal onto the blockwork at the edges of the lintel.
    • CommentAuthorIan1961
    • CommentTimeAug 14th 2015 edited
     
    <blockquote><cite>Posted By: richardelliot</cite>Should you have a vapour barrier anyway as I assume condensation would be a risk whether not you added some high performance insulation internally?</blockquote>

    If the plasterboard on your walls generally is the foil backed type then you probably won't need anything extra.

    The condensation risk comes from any warm moisture laden air from inside the house (bathrooms are obviously the highest risk rooms) coming into contact with a cold surface such as any exposed parts of your lintel - the moisture in the air then condenses out on that surface and can generate enough water to damage finishes such as the plasterboard.
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      CommentAuthordjh
    • CommentTimeAug 14th 2015
     
    who detailed the design?
  10.  
    It was done between the architect and the structural engineer (although the lintel specification almost certainly came from the engineer).

    It was well outside of my comfort zone to challenge the SEs drawings for thermal bridges. Generally things seem ok, but now we are onsite and I can see items coming out of the ground in 3D I'm having more questions.
    • CommentAuthortony
    • CommentTimeAug 14th 2015
     
    The insulation barrier should be all joined up, with no bridging.

    The architect does not seem to have done his job of overseeing different aspects.

    I would not accept that lintel solution, not the thermal bridging, nor the omitted insulation.

    If you can add sheet insulation to both inside and outside of the I section of the lintel and Unser it 25mm then cover with expanded metal and plaster

    Re dot and dab if you want to frighten yourself try http://readinguk.org/draughtbusters/?page_id=45
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      CommentAuthordjh
    • CommentTimeAug 14th 2015
     
    What Tony said.

    It depends on what the goal is - what the brief was - but I'd certainly be looking to get that improved and at this stage that probably involves remedial works and the question of who pays.

    You could add some insulation internally, either over the whole wall in that room, or over the part above the door and make a feature of it. I guess the tricky part will be accessing the cavity to add some insulation external to the lintel?

    I'd be nervous about fitting rigid insulation within the web of the lintel, in case small gaps allowed air and moisture to move and cause condensation in there. Perhaps fill it with spray foam? (I'm no expert and there may well be a reason not to do that).

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