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Green Building Bible, Fourth Edition
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General: Reducing cold bridge on timber frame with level threshold

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    I am looking at a timber frame house where the client is severely disabled, not withdstanding Part M, she will want level thresholds on all the external doors and there are lots of them.

    I have come unstuck on the slab-wall detail as the normal requirement of the timber sole plate being 150mm above ground level whilst trying to keep inside and outside and near the same level leaves me with an uninsulated blockwork upstand below the timber for 150mm.

    Generic detail attached.

    I wondered about making the blockwork plinth 100mm rather than 140mm and getting more insulation behind it or using a thermalite type block but I'm not sure this is a good plan for fixing down the timber frame.

    Are there any methods to ameliorate this problem, I can't be the first one.

    Regards
    Richard
    • CommentAuthortony
    • CommentTimeMar 1st 2011
     
    That detail looks really horrible with designed in thermal bridging -- I hope it does not get built like that

    There are lots of good details for thresholds in the book details for Passive Houses -- you can borrow my copy if you like.
  3.  
    Yup I know its bad.

    Any in there with outside and inside levels the same and the timber frame 150mm above ground level?
    • CommentAuthorpmagowan
    • CommentTimeMar 1st 2011
     
    Is the book in English as well as German?

    Thanks
    Paddy
    • CommentAuthortony
    • CommentTimeMar 1st 2011
     
    I have english copy so yes
    • CommentAuthorpmagowan
    • CommentTimeMar 1st 2011 edited
     
    Thanks Tony.
    Do you know if it has any details for above rafter insulation to EWI eave junction ('floating eaves') such as discused in my previous thread. I bought the complete guide to EWI but it had very limited information on these deatils and, in my opinion, the detailing included was full of thermal bridges and closer to UK spec than passivhaus spec. I would also be interested in the door detailing as above.
    Sorry for semi-hijack but I dont want to buy another expensive book to find there is less info in it than I can glean from here and the interweb!

    Thanks
    Paddy

    PS. this is the thread I allude to;
    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&page=1
    • CommentAuthortony
    • CommentTimeMar 1st 2011
     
    Yes detail "AWm 01 DAm 01" is there it shows it how I would do it using the counter-battens to carry the roof tiles and gutter past the insulation.
    • CommentAuthorpmagowan
    • CommentTimeMar 1st 2011
     
    Thanks Tony.
    Looks like a goer then!

    Thanks again
    Paddy
    • CommentAuthorTimber
    • CommentTimeMar 1st 2011
     
    You are not the first one, and the solution is fairly simple, infact, if you are a TRADA member, there are similar details to the one you are after, with calc'd and declared PSI values, as well as full marked up technical drawings.

    The jist is to create a 50 mm service void inside the 140 mm timber frame (helping to improve U value, air tightness and thermal bridging) and sit the timber frame on a perimeter upstand of blockwork. Inside, you can use this 50 mm to fit rigid PUR insulation linked with ground floor insulation and the insulation within the 50 mm service void.

    Timber
  10.  
    Thanks for that, I do have a service void but its less than 50mm. I'm going to look at using a 100mm blockwork upstand under the 140mm timber frame which should give me a more meaningful insulation thickness at the base, if the engineer is ok with that.
    • CommentAuthorCWatters
    • CommentTimeMar 2nd 2011
     
    These people make an insulated level access entry threshold which looks interesting...

    http://www.nevko.com/pages/nevko_external.htm
    • CommentAuthortony
    • CommentTimeMar 2nd 2011
     
    It looks very nice and it high quality -- I wouldn't call it insulated though
    •  
      CommentAuthordjh
    • CommentTimeMar 3rd 2011
     
    What do the "thermally broken" arrows point to if not insulation then?
    • CommentAuthorTimber
    • CommentTimeMar 3rd 2011
     
    Richard - Sounds like a plan, although I would bet you a pint that the structural engineer takes a sharp intake of breath when you mention this idea. Potential issues with rotational moments and stuff. You *could* go back to an 89 mm deep stud (+ 9 mm OSB/3), sat on 100 mm block, then batten and insulate up to the required thickness. That would get over any issues if the SE says 140 mm frame on 100 mm block won't work.

    Timber
    • CommentAuthortony
    • CommentTimeMar 3rd 2011
     
    djh -- yes there is some insulation present but in insufficient quantities and a lot too many thermal bridging paths.
  16.  
    You could replace the treshold block with a block of dense insulation or foam glass and you could put dense EPS or XPS in the cavity of the rising wall (below dpc). I've attached the Passive House Treshold detail we use.
  17.  
    Viking House,

    Would it be possible to provide some description of the numbers pointing?

    I have not even thought about this issue yet, I have ICF construction so was thinking I would simply set the door in line with the outer 150mm of EPS insulation so there is no issue then is there? I am sure I am missing the problem though? I love this forum but it makes my head spin :-)
    •  
      CommentAuthordjh
    • CommentTimeMar 4th 2011
     
    Posted By: tonydjh -- yes there is some insulation present but in insufficient quantities and a lot too many thermal bridging paths.

    Well I guess you're looking at something different to me. The one I'm looking at appears to have insulation stuffed in all kinds of places where I wouldn't think it was needed, and the specific thermal break looks like a typical one for aluminium extrusions. I don't see anything that I would call a thermal bridge in this context; that is a continuous path of high-conductivity material.

    Alternatively, can you point to a better product?
  19.  
    Posted By: Phil.Chaddah-DukeViking House, Would it be possible to provide some description of the numbers pointing?
    Hi Phil, The green is insulation and the grey is concrete.
    • CommentAuthorwookey
    • CommentTimeMar 4th 2011
     
    djh - those thermal breaks look exactly like the one used in the exitex aluminium thresholds: about 10mm of acrylic (with some foam in the box in this case). I've got one of the exitex ones and have found it to be a pretty poor insulator and the aluminium threashold is still a notable thermal bridge that collects a lot of condensation. It's well above the typical standard of thresholds, but personally I think it's very difficult to make a (thermally) good threshold out of aluminium. I've not seen one yet. Any metal bits need to not pass from one side of the door to the other. Something fibreglass or timber seems a much better bet - e.g. http://www.enduraproducts.com/docs-literature/lit-instruc-warr-sizes-pdf/web-prod-literature/newZFAM.pdf

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