Running pipes and electrics through PIR insulation

Discussion in 'Building' started by jamie765, 18 Jul 2019.

  1. jamie765

    jamie765

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    I'm putting the insulation in for my loft conversion and not sure how to put the Celotex around the pipes and electrics.

    I've had first fix plumbing done as shown in pics. Tried Googling and searching this forum but all answers were for wool insulation, not PIR.

    What's standard practice here? Do I cut two seperate pieces of Celotex for each section - one to put above the pipes and one to put below? Would some rockwool then be required behind the pipes?

    OR do I just one piece of Celotex for each section, and notch in a gap with a stanley knife for the pipes to run through it?

    Also wondering the same for the 1.5mm lighting cable and 2.5mm power cables. Is conduit/trunking required for these?
     

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  3. noseall

    noseall

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    I'd have filled the voids prior to fist fix plumbing. Is there any insulation externally running across the studs?
     
  4. ^woody^

    ^woody^

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    That is not the best design to have pipes embedded and inaccessible in an external wall. Should be in the floor in a duct. But if that's it, just fill it however you can with the same insulation and make sure there are no gaps.

    Sleeve and isolate cables from the insulation.
     
  5. noseall

    noseall

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    Same thoughts - that's why I asked I there is mebbe an insulation layer going on the inside. It could be an opportunity to duct the pipes at skirting level.

    If it is controlled work then there should be further insulation across the studs.
     
  6. jamie765

    jamie765

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    Not planning to put further insulation across the studs - building control were happy with 90mm Celotex in between studs (although they did want 25mm under the rafters and flat roof joists, both of which will have 125mm in between rafters/joists)

    Agree pipes would have been better run in the floor but left plumber to it for the day and came back in the evening to see it done this way!

    So best option is Celotex behind the pipes and in front of them...no rockwool?
     
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  7. ^woody^

    ^woody^

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    Pattern staining on the decorations it is then! :cautious:
     
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  8. noseall

    noseall

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    Exactly what I was thinking Woods. Those 4 x2's will transmit the cold and in a bathroom.:eek:
     
  9. jamie765

    jamie765

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    Pattern staining with 90mm between studs? I checked u values on different manufacturer websites a few weeks ago and to meet the required 0.28 u values you'd only need 100-110mm insulation between studs anyway (with no insulation required outside studs) - surely building control wouldn't allow no insulation over studs if it caused condensation and staining?

    FYI the bathroom will be fully tiled if that makes any difference
     
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  11. John D v2.0

    John D v2.0

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    Yes the overall u value would pass but you need to look up thermal bridging and check the"limiting u value" which for a ceiling is quite strict, and you should be especially careful in a bathroom due to humidity causing condensation.
    However for existing construction you just have to aim to insulate, rather than meet any particular standard, so maybe the building inspector is more relaxed
     
  12. ^woody^

    ^woody^

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    Building inspectors do not assess against quality, performance, best practice or many BS/EN standards. All they do is check for compliance against a set of very narrow basic criteria.

    BTW he is actually interpreting the performace of your wall incorrectly. Yes 90mm of Celotex in a timber frame could potentially acheive 0.28 on paper. But when you start to take account of the area of timber studs, and cut-outs for services, then the wall as a whole fails. You can potentially get away with it on small dormers with few timbers and no services, but otherwise you always need a layer across the internal or external face.

    Tiling may help in masking any surface staining, but the condensation risk is still there and it can still develop and then the issue is where does all that excess moisture evaporate to or penetrate? It is a risk that would normally be designed out.
     
  13. noseall

    noseall

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    Its not what is between the studs rather the studs themselves that are the problem.

    Every single 100mm thick frame we have built over the last 10-15 years has had 50mm of insulation across either the inside or outside of the studs. All our dormer windows are designed (width size wise) so that the dormer cheeks can accommodate the additional 50mm insulation plus plasterboard, without fouling the window jambs.
     
  14. pilsbury

    pilsbury

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    Not answering your question..... and not PIR..... but apparently cables don’t do well surrounded by EPS. But that’s not your concern. While I’m at it, dogs don’t like cats.
     
  15. jamie765

    jamie765

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    Excuse my ignorance...what's EPS?
     
  16. pilsbury

    pilsbury

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    Expanded polystyrene. The poor mans alternative. What I bunged in my floor.
     
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