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Airtightness detailing between old and new

47_Second_Ave | Posted in General Questions on

Planning a bolt-on extension targeting 3-5 ACH @ 50Pa. We’re based in Australia where Proclima has a good library for construction details. Plan is for ventilated facade + extasana for external walls + centralised HRV (this will only service the new extension, not the old part of the house) with an airtight door separating existing leaky house to airtight extension.

We are building a ensuite as part of the extension. However it will be connected to the existing house via a cavity slider door. Advice from the HRV supplier is to seal off the ensuite to the rest of the extension to ensure the HRV can function efficiently. Our PHPP assessor has suggested wrapping the ensuite in Intello to combat the airtightness issue. The ensuite will be serviced by a continuous extraction fan ducted to the outside of the house, so condensation risk should not be a problem.

Would using OSB instead of Intello in this case be sufficient to overcome the airtightness issue? Essentially, we’re just wanting to separate the old and new.

See attached photo – green for Intello/OSB, blue for Extasann, pink for potential double layer of XPS (pending WUFI analysis)

Replies

  1. Expert Member
    Akos | | #1

    It makes no sense to seprate that two unless you are looking for an air tight place to escape to during allergy season.

    Separating the two won't reduce energy use or make the HRV ineffective. What does matter is getting an air tight connection between the new and the old. Typically I've put a piece of lumber onto the old walls with flex adhesive. The sheathing of the new section now seals to this lumber for air barrier continuity.

    1. 47_Second_Ave | | #2

      Forgot to mention that the centralised HRV will only service the new extension, hence the need to separate the two, to ensure balance and efficiency.
      And the wife has bad allergies... :)

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