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Housing - New Build: Getting the layers rights for a timber frame wall

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  1.  
    • CommentAuthorsmallcog
    • CommentTimeAug 31st 2007
     
    Hello,

    I'm wondering if someone can point me in the right direction. I want to build a timber frame house with 30cm of insulation in the stud wall ( a double stud ) and then plaster the outside of the house. I can't find detail of how the timber frame house can take the plaster and keep its breathability.
    Does the following sound correct for the layers, starting from the inside out:

    1. Internal wall e.g. plasterboard
    2. Vapour barrier
    3. Stud frame with insulation ( a double 4x2 stud with spacers in between to make the 30cm )
    4. Waterproof membrane which is not vapour proof ( breathing )
    5. Layer of laths layed diagonally to allow air to circulate on outside of breathing membrane
    6. Sheathing, e.g. OSB
    7. Extruded metal mesh
    8. Plaster

    Any opinions on this or pointers to where on the web I can see other possible options ?

    many thanks

    Colm O'Gairbhith
  2.  
    I may be doing a very similar lay-up, but am still actively considering Breathing Wall. Have you thought of this? Have a look at Out of The Woods or The Whole House Book.
  3.  
    Over here in Canada, this is what we did - quite similar to what you propose but you have layers 4 and 6 transposed. From the inside out:

    1. 1/2" plasterboard
    2. 1x3 furring strips
    3. 1/2" foil-faced Polyisocyanurate foam board (acts as vapour barrier too)
    4. 2x6" studs (double 2x4 is excessive) with insulation
    5. 5/8" OSB sheathing
    6. Tyvek air barrier (moisture permeable but waterproof)
    7. 1x3 furring strips
    8. 1" thick wood siding

    Layer 8 could be brick, block, stone or anything - it's purely decorative and has no structural aspect. Search in this forum for "pressurized rainscreen construction" - the Canadian building research people have published several papers on this which detail this kind of construction.

    Cheers,

    Paul in Montreal.
    • CommentAuthorsmallcog
    • CommentTimeSep 2nd 2007
     
    Paul's example is what I had seen previously in the case where wooden siding is used. In this case there is ventilation between his layers 6 and 8, i.e. membrane and wooden siding, ensuring that the vapour passing through the membrane is evacuated. I've talked to a few plasters about my plan and they are proposing the following:

    1. Internal wall e.g. plasterboard
    2. Vapour barrier
    3. Stud frame with insulation ( a double 4x2 stud with spacers in between to make the 30cm )
    4. Sheathing, e.g. OSB
    5. Waterproof membrane which is not vapour proof ( breathing )
    6. Extruded metal mesh
    7. Plaster

    The reasons given were:
    A. plastering directly onto OSB/ply would cause the OSB/ply to rot over time
    B. The plaster, a "standard" plaster ( sorry for lack of details ) will soak the vapour from the insulation cavity through the membrane and will be carried through the plater and evacuated outside in the same way as plasters absorbs a certain amount of rain but dries out cyclically.

    I'll be calling the guru in CAT tomorrow to see what their opinion is, I'll post their views here. One advantage of the layers detailed in this comment is that the house can be wrapped in the membrane and then left for a considerable period while doors/windows and a plasterer are being sorted out.

    Best regards / Colm
    • CommentAuthorsmallcog
    • CommentTimeSep 2nd 2007
     
    Nick, I have the first edition of "Out of the woods" and "The Whole House Book" and neither have the detail required. Does the second ed. of " Out of the Woods" have more specifics ? On an aside, I'd love, or would have loved, if there was a book detailing, in detail, the actual construction of a house, where you could actually all materials lists and construction detail. I've gotten my frame up and the outside stud in place and such a book would have been a major help. That said, what I've built is still standing ( fingers crossed )
    / Colm
    • CommentAuthortomsusweb
    • CommentTimeSep 2nd 2007 edited
     
    Colm - you might be interested in my post here (be warned it could be crazy):

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=624

    For a more conventional breathing option that you could render onto, why not try the 'whole house book' approach (p. 194 2nd edition) which would basically be (inside to out):

    1. Internal finish (e.g. plasterboard)
    2. service space
    3. vapour check (e.g. Sisalkraft 410)
    4. Insulation and timber structure
    5. sheathing (e.g. Hunton Bitroc)
    6. airspace
    7. rainscreen (e.g. cement particle board with render on top - e.g. see here: http://www.greenspan.ie/aquapanel.htm)

    number 7 solves the membrane and osb issue which sounds messy to me!
  7.  
    Smallcog, the latest edition of Out of The Woods does have a brief ref to Breathing Wall. 'Simply Build Green' (Talbott), about the eco houses at Findhorn, has more. I am sure there must be serious erudite comment somewhere. Basically it's about having materials on the inner skin which are most vapour resistant, and the least resistant on the outside (ratio c 5:1).
    • CommentAuthorsmallcog
    • CommentTimeSep 5th 2007
     
    Thanks for all comments so far. The expanded metal idea may be put on the back burner while I do a bit more research. The OSB / membrane will be enough to get me through the next few months anyway while I think this through.
    • CommentAuthorsuecar
    • CommentTimeSep 5th 2007
     
    If you look on the following website: www.rounded-developments.org.uk you can find details of a timber frame breathing wall. There are the architects drawings for a passivhaus that is being built at the moment in Cardiff. It uses natural hemp/cotton insulation, fibre board and lime render.

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