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External wall insulation - Proving code compliance ?

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  • External wall insulation - Proving code compliance ?

    Evening all ... first post

    I'm doing my own design, consent and build under an owner builder exemption for a new family home we've purchased in Auckland. The work will involve some exempt items as well as a new deck and insulation to external walls. I'm fine with the fact I require consent for these things and confident I can prepare things to an adequate quality to lodge.

    What I'm struggling with is finding ways to prove building code compliance for the retro-fitted external wall insulation. There is little to go on and I refuse (at this stage) to pay an expensive wizard to generate (copy) a specific (generic) design.

    Has anybody had experience with retro-fitted external wall insulation consents and can advise how performance was proven to meet code ? I'll have a mix of direct fixed Hardiplank on timber frame and brick veneer.

    My current plan: Run with 70mm R2.2 glass batts set back 20mm from the building paper / cladding or brick cavity based on information out of NZS 4246:2016

    Happy to share my experiences if of interest when this is all navigated successfully

  • #2
    With a refurb, you can either retrofit insulation to meet current H1 code requirements, or you insulate to a level as reasonable as practical, see Section 112 ANARP which specifically allows for upgrading (or not) of parts of a building.
    This site can be helpful to explain this: https://www.building.govt.nz/buildin...ting-building/
    To prove H1 compliance, you can use these tools: https://www.branz.co.nz/H1_support

    As an alternative to your method of insulation, have you considered kingspan kooltherm insulated panels, these are sandwiched PIR insulation and Gib plasterboard panels, you can install these on top of your existing internal plasterboard - no need to remove the old plasterboard and they give higher R-values for equivalent glass batt widths.

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    • #3
      From what I've researched the H1 requirement is not triggered by retrofitting insulation into external walls as per the second paragraph in the link below:

      Turns out I can't paste a link but if you google "Appendix A - Building Code performances that retrofitted insulation" you should get to the right document.

      I'd assume the relevant clauses to comply with would be:
      - B2 Durability ... easy enough as all of the products used have BRANZ appraisals or similar technical documentation
      - E2 External Moisture ... this is the one that I'm struggling with (assuming its required)
      - G9 Electricity ... maybe, again looks fairly straight forward

      Thanks for the Kingspan link, but I'd like to try and get it consented as a standard sort of upgrade if possible.

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