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General: Extend insulation on timber-frame parts of house

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  1.  
    • CommentAuthorminisaurus
    • CommentTimeFeb 13th 2023
     
    See piccy - our house is a mixture of timber panels on timber frame and concrete block walls - an 80s Swedish affair with a plastic-bag (subsequently occasionally perforated) vapour barrier around the internal plasterboard.

    When renovating, I'm considering increasing the insulation of the timber frame parts - i.e. remove timber panels, add new framework to increase insulation width, add insulation, and replace the timber panels.

    The existing insulation on the timber parts is approx. 12cm thick.

    I'm concerned that this may create/shift dewpoints in the timber frame, or even where timber meets concrete.

    What do others think?
      house.jpg
    •  
      CommentAuthordjh
    • CommentTimeFeb 13th 2023 edited
     
    Posted By: minisaurusplastic-bag (subsequently occasionally perforated) vapour barrier around the internal plasterboard
    It'd likely be a good idea to go around and make sure as many of the perforations as possible are taped up.

    Posted By: minisaurusremove timber panels, add new framework to increase insulation width, add insulation, and replace the timber panels. ...

    ... I'm concerned that this may create/shift dewpoints in the timber frame, or even where timber meets concrete.
    Generally EWI moves the dewpoint inboard, so further away from external timber cladding. It warms up whatever's inside!

    edit: sorry - that 'inboard' should read 'outward'. :cry:
    • CommentAuthorminisaurus
    • CommentTimeFeb 14th 2023
     
    Yeah, I’ll try and check out those perforations.

    Re. dew point, I was thinking I might start getting it on the old/existing 12 cm deep timber frame parts, once they’re covered with the new insulation?
    •  
      CommentAuthordjh
    • CommentTimeFeb 14th 2023
     
    Posted By: minisaurusRe. dew point, I was thinking I might start getting it on the old/existing 12 cm deep timber frame parts, once they’re covered with the new insulation?
    Sorry I made a silly mistake in my last post - I meant the dewpoint is moved OUTward. So you're even less likely to get condensation inboard of the EWI on existing materials.
  5.  
    You need the outside covering to be breathable, so that any moisture that finds its way in can escape, rather than be trapped in the colder outer regions of the wall. Eg with breathable paint on the timber cladding.

    Or alternatively with an air gap between the insulation and the cladding, maybe 50mm, with gaps at the top and bottom for air to circulate behind the cladding and carry away any moisture that finds its way in there. With this option you need to be careful that birds, mice, wasps, fires cannot get in the gap, there may be different building laws about this in your country.

    In some countries there are problems with insulation and internal plastic barriers if it is warm and humid in the summer. I don't know much about your climate (sorry!) if this applies to you or not.
    • CommentAuthorminisaurus
    • CommentTimeFeb 14th 2023
     
    ha ha - okay - OUTward, good to know, thanks.

    Climate is Sweden; the praxis here is usually to leave an airgap between the insulation and cladding, preferably with some kind of insect and mouse net at the top and bottom, although quite often this seems to be missing ...
    •  
      CommentAuthordjh
    • CommentTimeFeb 14th 2023
     
    Posted By: WillInAberdeenYou need the outside covering to be breathable, so that any moisture that finds its way in can escape, rather than be trapped in the colder outer regions of the wall. Eg with breathable paint on the timber cladding.
    Isn't it a case of it needs to be breathable iff it is breathable?

    Since the EWI moves the dewpoint outward, everything inside it should be above the dewpoint so there's no condensation risk inboard of the insulation. So if there's water vapour at the inner surface of non-breathable EWI it will still be vapour and won't condense. As long as there is sufficient EWI.

    Water coming from the outside should be resisted by the cladding and drainage plane. That's their main purpose in life. Certainly liquid water should be able to drain out.
  8.  
    That's broadly correct, but dewpoint depends on humidity as well as temperature. The VCL on the inside is known to be perforated, so if the outside face of the wall was to be made impermeable, then humidity levels would increase within the insulation, increasing the dewpoint temperature. In that case, and as there is already 120mm of insulation in the existing wall, the new EWI would have to be extremely thick, if it were desired to keep that increased dewpoint temperature outboard of the timbers, during a Swedish winter.

    However minisaurus is planning an airgap to allow the construction to breathe. So long as the new external insulation material is also moderately breathable then all will be ok. Snowy weather is particularly good for sucking moisture out of breathable walls, the cold air gets really dry.

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