Flat roof question

Discussion in 'General Discussion' started by jivedubbin, Nov 1, 2019.

  1. Does anyone know if I would need a timber wall plate for rafters on a flat roof ,the wall the rafters are going to sit on is brick work,
    I'm trying to reduce the overall height so I don't end up with a huge facia . IMG_20191031_081048456.jpg this is the roof from above ,I intend to leave the existing in place and fill the void with insulation as there is none at the moment
     
  2. crossy2112

    crossy2112 Supporter

    You would have to strap the joists down to something to stop it blowing off and pack each joists to get them level but yes should be ok
     
  3. crossy2112

    crossy2112 Supporter

    Just a thought, why not fix a plate inside where you are going to insulate and fix your joists to that.
     
  4. I like that idea I will have a look at that
     
    crossy2112 likes this.
  5. Dub and Dubber

    Dub and Dubber Supporter

    As it's not a case of adding a load bearing floor, to keep the profile down wouldn't it be enough to fill that "well" with celotex type boards bonded to what's underneath, and then bond strandboard/OSB/Sterlingboard onto that, and "felt" over the whole ...
    Profile only goes up by about 25mm .......?
     
  6. Dub and Dubber

    Dub and Dubber Supporter

    .... and you can still keep the drain points if you wanted to
     
    Purple likes this.
  7. I need to get a fall on it ,the wall is level all the way round,I I was planning on using 150 joists with fitting pieces and OSB then filling the void with fibreglass up to a depth of 300 mm which is a lot cheaper than celotex ,also the OSB needs fixing to stop it flexing
     
  8. Dub and Dubber

    Dub and Dubber Supporter

    Do you mean putting a taper on the "joists" to get the fall?
    A Celotex type board, like Quintherm say, would only have to be half to a third as thick as the fibreglass to get the same insulation value .... so in that sense it costs the same-ish?
    Also if you cross batten instead of using full depth joists, you'll massively reduce the thermal bridging ... You could do the build up with cheap-as-chips treated tile battens .......?
     
  9. If you use lead flashing on the new roof, don't publish your address on here...
     
    Suss, Purple, crossy2112 and 2 others like this.
  10. At it's wide it measures 3.6 m across that span it calls for 150 X 50 mm timbers .I'm a bit concerned that anything less would dip in time and create a pond ,so how would you cross batten it and still get a fall .
    The fall needs to be 1:40.
     
  11. There will be lead but not worth traveling the distance
     
    snotty likes this.
  12. Dub and Dubber

    Dub and Dubber Supporter

    I might be reading this wrong but are you not just adding some insulation and a capping to an existing roof that has its own rafters?
    (by doing away with the well)
    If so all those rafters will have to support extra is the insulation (negligible) and the capping boards.
    Celotex type boards won't compress or sag in time like fibreglass could.
    Fall would come from spacers ....
    Just doing toast so gtgb!
     
  13. the rafters are only going to support the OSB and the felt and to give it a fall ,installation will be under and between the rafters
     
  14. so I've had a look at that idea it looks feasible the shallowest place is only 100 mm deep so I would have to shape the timber to accommodate the curve of the felt that it looks like a good idea actually
     
    Dub and Dubber likes this.
  15. Dub and Dubber

    Dub and Dubber Supporter

    Could you bung up a drawing at some point, then I can "reply" with my own :thumbsup:
     
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  16. Dub and Dubber

    Dub and Dubber Supporter

    Is this the cross section you've got?
    IMG_20191101_150306571.jpg
    and are there two falls at the moment, (like a shower tray) towards that drain point bottom left?
    ... and which way did you want your new fall to go?
    (Single fall away from the main building?)
    ... and would you be doing gutters around it etc?
     
    Last edited: Nov 1, 2019
    jivedubbin likes this.
  17. 2019-11-01 15.06.44.jpg
    Bad drawing but that's what I'd do your not removing any of the timber underneath are you? What about ventilation
     
  18. Best to finish with a rubber bonded roof covering EPDM


    Sent from my iPhone using Tapatalk
     
    Purple likes this.
  19. I would fall to the left. But run gutters all round to make it look nice
     
  20. Lots of people don't like rubber but to be honest I did a small flat roof (my house)10m x4 6 years ago or maybe more it's still 100,% fine it gets very slippy thou
     

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