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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorPeter A
    • CommentTimeMar 27th 2007
     
    Needed some pearls of wisdom from the forum. Trying to persuade fellow developers that high levels of insulation is the secret coupled with good air leakage. Build timber frame so off to a good start, working along lines of service void on walls so that vapour barrier can remain intake (no perforations).
    But what about the upper floor void, how do you maintain the integrity of the vapour barrier or am I worrying unneccessarily, could really do with some advice from the Passivhaus/Canadian experts on air leakage.
  1.  
    Hi Peter,

    leakage between floors is rather easily solved. In our new build, the join between the ground floor and first floor where the floor trusses meet the external frame were simply sealed with closed cell polyurethane foam that was applied before any other insulation or interior finishing was added. Closed cell polyurethane is a vapour barrier so there wasn't an issue here. Same thing was done at the rim joist (where the wooden framing sits on top of the concrete foundation). After the foam was applied, insulation was added to the wooden frame and then foil faced polyisocyanurate foam board was glued to the studs and sealed using acoustic sealant to the polyurethane foam. This polyiso layer also is a thermal bridge as 1x3 strapping was added on top of this and the interior gyproc then screwed to the strapping. Electrical outlets were encased in a vapour barrier which was then taped to the front of the polyiso boards using "tuck tape". The main air leakage barrier, of course, is external to the wooden frame and is also taped at all joints.

    Hope this helps,

    Paul.
    • CommentAuthorPeter A
    • CommentTimeMar 28th 2007
     
    Paul, was rather hoping you would come to my aid, it's at the rim beam/joist at 1st floor level that I have concerns, you mentioned that the main air leakage barrier is on the outside of the timber frame, which face, in the uk it's on the room side of the frame. I want to create a vapour barrier in the floor void where the joists abut the rim beam and it all seems a bit of a fiddle and an area prone to bad workmanship, I need a detail that is robust an can be done with out too much thought, appreciate that I might be asking too much but it does have to be simple in a mass market.
    • CommentAuthorGuest
    • CommentTimeMar 28th 2007
     
    Me thinks that a major problem looms on the scale of the New Zealand problem only very much bigger concerning vapour control layers inside timber walls. Some designers think that if they draw a line on a paper or screen and call it a vapour barrier that vapour will exist at on one side of this line and no vapour on the other side of this line. Not quite comprehending that a tiny hole such as made with a staple or a breakdown in seals or tape - which are almost 100% derived from petrochemicals and which have a limited life of average about 7 years before the adhesion gives out - will cause a build up of water molecules inside a timber frame wall with no venting. This is guaranteed to cause a problem just after the 10 year warranty expires.
    Our climate which is similar to New Zealand is not suitable for timber frame unlike Scandinavian countries and Canada where most of the water is ice.
    • CommentAuthorJohan
    • CommentTimeMar 28th 2007
     
    Peter,

    You can also have a vapour barrier in the ground floor ceiling (below the joists) and maybe in the first floor floor (above the joists). You can probably leave the first floor barrier out though as the natural airflow is upwards anyway.
    That will stop any internally generated moisture from enterering the floor void. Paul's solutions is as good though. What ever is easiest for you! :smile:

    Guest,

    Sorry, but I disagree completely with that...

    A vapour barrier in a wall is only good for stopping any vapour generated inside the building. However, with a well insulated, well ventilated house you get very little condesation anyway. A timber framed wall is always breathable on the outside...

    In Sweden in the 70's it was very popular to use plastic paints on the outside walls (as it is in Britain currently...) as they were sold as maintenance free. 10 years later it showed out that it wasn't such a good idea as the timber cladding rotted away nicely... :sad:

    There's no reason why you shouldn't use a vapour barrier in a house in UK.

    btw, when ice melts it turns to water...
    • CommentAuthorPeter A
    • CommentTimeMar 29th 2007
     
    Posted By: GuestMe thinks that a major problem looms on the scale of the New Zealand problem only very much bigger concerning vapour control layers inside timber walls.


    Oh dear I wonder what we will do with all the timber frame units built in the UK over the last 30-40 years! I have to say that I believe you are wrong and am in total agreement with Johan.

    Johan thanks for your input, I wanted to avoid vapour barriers on ceilings if at all possible as they are prone to abuse on site with the number of service penetrations which would be difficult to police on large developments, want to get to a situation where the vapour barrier is in on the external frame, all services run, windows in, the vapour barrier can then be signed off before allowing boarding to occur. So really need to come up with a simple solution for the rim beam zone that still allows the timbers to breathe.
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