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    • CommentAuthormarsaday
    • CommentTimeMay 23rd 2018 edited
     
    Hi all

    This is my second posting on this topic. I posted initially before any construction last spring.

    I have been working hard since then and have built some of the extension. I had to stop for winter because the tile / glass roof needs to come off and i am tackling that from end July till sep hopefully.

    Anyway i have a question again about my oak purlins which will sit from left to right in the extension and will support the roof structure. There are 4 beams basically:

    1) An oak wall plate fixed onto the back wall of the house

    2) A 5m oak beam sat where the line of the two patio doors are positioned. The brick column between these doors will also go.

    3 & 4) Will be 6.5m beams spanning the full width of the extension and will be set at equal distances as the room moves out towards the new french door opening. These beams will be supported also on the wall dividing the utility and main new room.

    Over the oak beams will be 125mm basic joists. These will need to sit comfortably onto the oak beams.

    On my other post about this issue it was felt the best solution was to tilt the beams so they flow with the joists above. This will mean zero bird mouthing. This is how i think i am going to do it BUT i wondered if this idea was worth considering.

    Place the beams in flat, but obviously in a slight decline which will match the fall of the roof. I think the fall is going to be around the 9-11 degree pitch. This will mean i will have a wedge gap to make up.

    So do you think cutting my own wedges in the same joist softwood could be an option ?

    The wedge would be 150mm long and probably about 20mm deep tapering down.

    The reason why i ask about this is that i think it will be easier to position the beams in flat, rather than on a tilt.

    No 2 beam is also a little bit more concerning as this will not have any wall behind it which will lock the beam into place. It will tilt and rest on a wall either side, but it will be open at the back because there is no need for the walls to go right back to the rear of the house.

    No 3 and 4 beams will be dissected by walls and at three points, so will be firmly locked into place.
    • CommentAuthormarsaday
    • CommentTimeMay 23rd 2018
     
    above extension
      IMG_1698.jpg
    • CommentAuthormarsaday
    • CommentTimeMay 23rd 2018
     
    from the garden
      IMG_1695.jpg
    •  
      CommentAuthordjh
    • CommentTimeMay 23rd 2018
     
    Posted By: marsadayNo 2 beam is also a little bit more concerning as this will not have any wall behind it which will lock the beam into place. It will tilt and rest on a wall either side, but it will be open at the back because there is no need for the walls to go right back to the rear of the house.

    No 3 and 4 beams will be dissected by walls and at three points, so will be firmly locked into place.

    A plan would be useful to visualize this arrangement. Apologies if you've already posted one elsewhere, in which case a link to it would be helpful.
    • CommentAuthormarsaday
    • CommentTimeMay 24th 2018
     
    I have done this rough drawing for you. Hopefully it will give you the info you need.

    Oak no 2 is not full span, but 5m only. It will sit on a new block wall created on the right side and a new block opening for the utility door on the left side. This will have a concrete lintel over the door, so will be structural.
      Scan.jpeg
    • CommentAuthorgoodevans
    • CommentTimeMay 25th 2018
     
    We are talking here of spans of up to 5.0/ 6.5m at perhaps 1m centres or more and load bearing. I'm guessing a SE has signed off on the beam sizes - if so he/she won't like you flipping them over on their side.
    • CommentAuthormarsaday
    • CommentTimeMay 25th 2018
     
    No the beams are good for 4.5m span.

    My opening is 4.44m. Then I get a wall break for the next section of open span of 1.6m

    So the beams will be tilted slightly if I go that route.

    Is my wedge option a good one though ? Apart fro the time factor I can’t see any issues with it
  1.  
    IMO I don't think it matters whether you tilt the beams, wedge the joists or cut a birds mouth. There is an aesthetic element about tilting the beams or having them perpendicular - personal choice or more likely SWMBO.

    You will either be wedging the beams to get the tilt or wedging the joists to account for the fall. IMO If you wedge the joists you should fix the wedges to the joists (glue and screw)
    • CommentAuthormarsaday
    • CommentTimeMay 25th 2018
     
    Thanks Peter

    I think it will be easier to put the beams in flat and then wedge my 22 joists.

    Yes i would glue and screw the wedges in place.
  2.  
    Just a thought, how will you finish the ceiling? If you are going to put plaster board on the joists between the beams then on the up side there will be a gap of the thickness of the wedge to hide.
    • CommentAuthormarsaday
    • CommentTimeMay 25th 2018
     
    Yes your right.

    Plaster board is going under the joists.

    I suppose i will cross baton the joist with roofing lat 25mm i think. That should take out the wedge difference.
  3.  
    Posted By: marsadayPlaster board is going under the joists.

    I suppose i will cross baton the joist with roofing lat 25mm i think. That should take out the wedge difference.


    Do you mean to use the cross batten as a 'decorative beading' to hide the gap or will you use this to mount the plaster board?

    If it is to mount the PB then assuming you put in a PB screw every 40cm then you will need a cross batten (decreasing in thickness) every 40cm and then you have the problem of hitting the battens

    Alternatively you could make a wedge going from 25mm to 0 to fix to the underside of the joists which avoids the hit and miss of the cross battens.

    This is where a table saw would be useful

    Or make sure the 'decorative beading' cross batten is a nice bit of moulding.
    • CommentAuthormarsaday
    • CommentTimeMay 25th 2018
     
    To mount the PB.

    Yes the wedge could be made up at the timber yard.

    This problem is fixable, but quite far in the future at the mo.
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