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Can a timber framed house be externally insulated?

  • 01-11-2022 7:34pm
    Registered Users Posts: 23 Biffoland

    I’m living in a timber framed house with poor insulation. I looked into bead insulation for the cavity but was told this will disrupt the flow of air and rot the timber. Have since confirmed this from a number of sources.

    I rang a contractor last week about external insulation for the house but he told me that this would also lead to the timber rotting.

    Can a timber framed house be externally insulated. If not, what’s the most suitable type of insulation?


  • Assuming it's a standard build, a timber frame house will be (from the outside in) cladding (usually masonry), ventilation gap, breather membrane, timber frame, interior plasterboard. If you fill the ventilation gap, the timber frame will slowly rot— the breather membrane & gap allows moisture in the timber frame to escape. And there's no point in insulating the cladding on the outside because of the ventilation gap.

    Theoretically, if it isn't masonry cladding & can be easily removed, you could remove the cladding, put wood-fibre insulation on the outside of the timber frame, and build up a new ventilation gap.

    Working on airtightness will probably deliver better results easier than insulation I would guess.

  • Moderators, Society & Culture Moderators Posts: 35,444 Mod ✭✭✭✭Gumbo

    Typically no due to the timber needing ventilation.

    If you do as the poster above mentions, you enter a whole new world of certification and issues around IS440 Compliance and Agrement Certificate compliance IMO

  • Registered Users Posts: 7,643 ✭✭✭Furze99

    Adding insulation inside would seem to make most sense in that situation. I think as a layman DIYer in such matters.

  • Registered Users Posts: 2,723 ✭✭✭MicktheMan

  • Registered Users Posts: 23 Biffoland

    Thanks for the replies folks. Looks like I’ll focus on air tightness then

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  • Registered Users Posts: 30,896 ✭✭✭✭Lumen

    Why would the timber rot if the dew point is in the external insulation?

  • Registered Users Posts: 751 ✭✭✭C. Eastwood

    If insulation between the timber studs of the timber frame becomes saturated with interstitial condensation- then Dry Rot spores in the timber frame will germinate, and Dry Rot will cause severe damage to the timber frame.

    The Safest way to insulate a Timber Frame house is to fix insulated slabs on over the existing internal plasterboard slabs.