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Laying out flat roof joists

Discussion in 'Building' started by Robster_1981, 27 May 2020.

  1. Robster_1981

    Robster_1981

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    Hi all

    I’m currently self building (or mostly self building) a 3m x 5m single storey rear extension, and the next job looming is the roof.

    I’ve got no drawings, so I’m designing stuff as I go, which has been interesting to say the least!!

    I’ve had a brickie in to build the walls, which are finished, but the block work is higher than the outside skin. It’s a cavity wall with 7N concrete block inner and 73mm brick outer skin. I think this is the reason for the difference in height (about 45mm). When I’ve asked him about it, he said that it will all get covered up when the fascia and soffits go in.

    I’m building the roof myself, and I’m doing a warm roof, and I’m a little concerned that the fascia’s are going to be huge to cover the 200mm joists, 120mm insulation and the extra 45mm from the higher block work.

    the way I see it, I have 3 options...
    Cut 45mm off the top of the blocks.
    Build the outer skin up one course, then bed a wall plate on the blockwork to make it even, or
    Leave it as it is and just have a 50mm deeper fascia to cover it.

    Any opinions.

    Oh, I didn’t really discuss the finer points with the brickie. He just knew that I was having a flat roof
     
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  3. noseall

    noseall

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    You could always finish the deep joists short of the brick-work, add some less deep cradling (fix timber extenders to the side of the joists) that extends to the outer masonry, then build up the brickwork to the underside of the extenders.

    It will result in taller looking brickwork with a bit of an odd depth of masonry above doors and windows though.

    We did this once - bit of a faff...
     
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  4. Robster_1981

    Robster_1981

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    That’s some job that! Looks great! Something to think about.

    another thing I’ve noticed on your picture is the weep vents above the opening. He hasn’t put any in on mine. The brickwork is straight onto a catnic style steel beam with no cavity tray. He said we don’t need one?
     
  5. Notch7

    Notch7

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    its because the brickie couldnt be arrised to cut the blocks, so he has created a problem for you

    cutting the blocks is a non starter as they are Hi 7s.

    you could cut a 45mm slot out of the joists -it wont be enough to weaken the joist bearing and it will reduce the fascia height by that much.

    whatever you do, it looks much nicer if you do a stepped fascia -so the main part where the gutter goes is no more than say 200mm.

    Also It looks nicest if you put a gutter all the way around -having gutter one side only with upstand on the others is ugly

    fitting an ogee style deep gutter disguises the fascia as well -although if your house gutters are a prominent feature you may want to match.
     
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  6. Robster_1981

    Robster_1981

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    Thanks Notch, that’s what I thought tbh :rolleyes:

    I like the idea of notching the joists and the stepped fascia, think I’ll go with that!

    about the weep vents...are they needed?
     
  7. oldbutnotdead

    oldbutnotdead

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    As a slight diversion, what roof covering are you planning on? If GRP then be wary, there are a fair few threads about GRP decks being very noisy on warm rooves.

    Weep vents and trays should be above all the openings (and set into the wall above where the extension joins the existing house if that wall is cavity as well), can't really blame the brickie, he could have mentioned them to but you're the project manager so your call
     
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  8. johnny2007

    johnny2007

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    Ask the brickie to come back, take last row of blocks down and cut them to size.
    It's your home, don't bodge it.
    If he wants a day work because this wasn't discussed, well let that be it, at least you won't have sleepless nights thinking about that.
     
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  9. ^woody^

    ^woody^

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    I would not be so generous to offer daywork.

    It's wrong, it should not have been done, it should not be paid for - nor to correct it. It should not need to have been discussed and any proper brickie should know how to finish a wall for a flat roof.

    Fascias are deep enough and border on crap-looking when done normally, and no way should they be made deeper.
     
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  11. Robster_1981

    Robster_1981

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    :confused::confused:
    thanks for all the advice!! I think I’m gonna take the top course down and just re-do it myself to save the agro!

    I’m doing an EPDM covering, so I’m going to lap it down over the edges and do a stepped fascia. Not quite sussed out the best way of doing it yet, but I’ll get there...on a side note, pvc fascia is so bloody expensive!!
     
  12. johnny2007

    johnny2007

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    If done properly you do it once and never change it again.
    You just clean it occasionally or do like me, give an extra to the window cleaner and they'll do it for you once a year.
     
  13. Robster_1981

    Robster_1981

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    One thing I didn’t ask. I’ve not had a wall plate put on, so I’m planning on strapping down every third joist (400mm centres). Sound ok?
     
  14. ^woody^

    ^woody^

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    Sounds normal, except twisted strap every 1500mm would do.
     
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  15. oldbutnotdead

    oldbutnotdead

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    Have a good search online for your fascia- I needed 400mm for the garage (JJ I beams) a few years ago, best price I found was about £5/metre from this lot https://www.speedyplasticsandresins.co.uk/ . Eurocell wanted something obscene......
     
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  16. Robster_1981

    Robster_1981

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    Awesome!! Thanks fella’s!! :cool:
     
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