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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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    • CommentAuthorgravelld
    • CommentTimeMar 5th 2018
     
    I'm working on how I communicate how I want my gables extended. Currently there's a 30mm overhang, so given I want 200mm EWI (and I don't want some dodgy EWI cap) I need to extend the rafters.

    I researched "flying rafters" and "gable ladders". Most of which came up appeared to be newbuild. A few retrofit projects did come up:

    https://passivehouseplus.ie/magazine/upgrade/cork-bungalow-upgrade-phased-over-12-years

    https://springdalegarden.com/tag/gable-end/

    I kind of copied this in a concept drawing, see attached. However a couple of questions:

    1) Cutting the "noggins" (my name for them, the horizontal timber between the current last rafter and the flying rafter) into the wall seems like a lot of work, is there a way to avoid that while keeping the current roof height?

    2) Related to that, I have asked two roofers who were here on other jobs for their ideas - both independently suggested using metal (steel) instead of timber. I see little mention of this around, thoughts?
      flying_rafter.JPG
    • CommentAuthortony
    • CommentTimeMar 5th 2018
     
    Probably no need for the noggins, the battens will hold the rafter and fascia up with a presumed 30mm oversail again
    • CommentAuthorgravelld
    • CommentTimeMar 6th 2018
     
    The roofing battens that hold the membrane down??? :shocked:
    • CommentAuthoradam_w
    • CommentTimeMar 6th 2018
     
    Dan,

    Could you fit the EWI first all the way up, then clamp the Flying rafter on the outside with the use of some threaded bar fixed in to the outer leaf with a resin anchor and then shored up as Tony is suggesting? Might be a little tricky getting the resin in the hole through 200mm but it could work!
  1.  
    If as tony said "Probably no need for the noggins, the battens will hold the rafter and fascia up" with which I agree, I would ask what is the purpose of the flying rafter? I would have thought that the extended battens would be strong enough to hold a tile with a soffit fixed to the underside of the battens.
    • CommentAuthorgravelld
    • CommentTimeMar 6th 2018
     
    Well ok, let's start from first principles. Let's ignore the flying rafter; the aim is to simply extend the gable.

    Peter, can you clarify what you mean by "batten" here - which batten?

    Ah, that reminds me, I remember more detail about the "metal" solution now. One roofer was suggesting forming "n" shaped metal brackets, fixing them over the existing horizontal roofing membrane battens and having them form the overhang (so they are "hollow" underneath once they cross the existing wall).

    In these cases, is there no need to cut into the existing wall?

    Is some sort of frame running parallel to the verge to tie all the battens together not required? Just thought it might add to the strength...

    The wall is, say 100+60+100 (inner leaf + cavity + outer leaf) and the new overhang would be 250=200+10+40 (EWI+finish+overhang).
    • CommentAuthorgravelld
    • CommentTimeMar 6th 2018 edited
     
    Posted By: adam_wCould you fit the EWI first all the way up, then clamp the Flying rafter on the outside with the use of some threaded bar fixed in to the outer leaf with a resin anchor and then shored up as Tony is suggesting?
    Thanks - the flying rafter is not there for aesthetic reasons. I just thought it was the way "this is done"!



    Well ok, let's start from first principles. Let's ignore the flying rafter; the aim is to simply extend the gable.

    Peter, can you clarify what you mean by "batten" here - which batten?

    Ah, that reminds me, I remember more detail about the "metal" solution now. One roofer was suggesting forming "n" shaped metal brackets, fixing them over the existing horizontal roofing membrane battens and having them form the overhang (so they are "hollow" underneath once they cross the existing wall).

    In these cases, is there no need to cut into the existing wall?

    Is some sort of frame running parallel to the verge to tie all the battens together not required? Just thought it might add to the strength...

    The wall is, say 100+60+100 (inner leaf + cavity + outer leaf) and the new overhang would be 250=200+10+40 (EWI+finish+overhang).

    AT is interesting here in incremental retrofit...
    • CommentAuthorMarkyP
    • CommentTimeMar 6th 2018 edited
     
    I had to do this for my EWI. The joiner had extended a gable overhang it before and suggested metal box section (50mm x 25mm I think), run across two inboard rafters, recessed into the rafters flush with surface, a small chase into the blockwork, and then hang the new gable rafter from this cantilever. You could do the same with timber. In the end we did it the way Tony suggests and left the tiling battens and the sarking to take the load as we only needs to create a 150mm overhang.
  2.  
    Posted By: gravelldPeter, can you clarify what you mean by "batten" here - which batten?

    Tile battens

    Posted By: MarkyPIn the end we did it the way Tony suggests and left the tiling battens and the sarking to take the load as we only needs to create a 150mm overhang.

    It would seem that others have done this before.
    • CommentAuthorgravelld
    • CommentTimeMar 6th 2018
     
    Posted By: Peter_in_HungaryIt would seem that others have done this before.
    Sorry... who?
  3.  
    Posted By: gravelldSorry... who?

    I thought MarkyP said that
    Posted By: Peter_in_HungaryPosted By: MarkyPIn the end we did it the way Tony suggests and left the tiling battens and the sarking to take the load as we only needs to create a 150mm overhang.
    • CommentAuthorgravelld
    • CommentTimeMar 6th 2018
     
    Ok. Should I talk to a SE about whether extending the tile battens will carry the load over the distance I need, or are the calculations documented somehow?
    • CommentAuthorSilky
    • CommentTimeMar 11th 2018
     
    I bookmarked this a while back, maybe useful (basically steel extensions to fit to existing battens, available in various sizes ) https://www.dachdeckermarkt24.de/6205-dachlatten-verlaengerungen-baustatisch-geprueft.html?number=DM02428
    • CommentAuthorgravelld
    • CommentTimeMar 12th 2018
     
    Very interesting, thank you.

    In the second picture it appears to show that the timber battens are continued the "other" side of the verge. Not sure why.

    A-ha, I found a video: http://www.lemphirz.de/produkte/dachlattenverlaengerungen.html which confirms that.

    This is potentially awesome, will have to check with BC.
    • CommentAuthorwookey
    • CommentTimeMar 17th 2018
     
    I need to do this too. That lemphirz thing does look like a very neat solution. I've seen people doing this in the UK by just screwing an extra bit of batten beside the original. That would make them offset by one batten-width though so I'm not sure exactly how it was done. (I was just passing the house). There is some kind of 'plate' the tiles are set on. Not sure if it's galv steel or asbestos-a-like sheet. I need to go and take a row of tiles off for a proper look/plan. I guess you end up extending by an integer number of tiles, whatever that width is.
    • CommentAuthorgravelld
    • CommentTimeMar 17th 2018
     
    Yeah, I think extending by a round number would be expedient. Would be interested if you learn any more from that house you've seen.
    •  
      CommentAuthordjh
    • CommentTimeMar 17th 2018
     
    The lemphirz video is slightly different in that they don't fix a long batten down the ends of the new stub battens, they just fix the tiles to the stubs. So it would be more difficult to fix a verge board. I don't see what would prevent fitting such a verge batten; it might extend past the edge of the tiles though? Need to check with the manufacturer.

    The purpose of the new timber stubs is pretty obvious; it gives somewhere to use a normal fixing to fix the new tile to the extended batten. What isn't clear is whether it is 'allowed' to continue the new stub battens further than the end of the metal piece to add more than one row of tiles. i.e. what the certified use is.
    • CommentAuthorgravelld
    • CommentTimeMar 17th 2018
     
    Posted By: djhThe purpose of the new timber stubs is pretty obvious; it gives somewhere to use a normal fixing to fix the new tile to the extended batten.
    Obvious to you :wink: . Thanks!
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