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Thread: Advice - any glazing, structural eng, builders able to help

  1. #1

    Advice - any glazing, structural eng, builders able to help

    Morning, just looking for some help or advice for anyone her who is involved with or has experience of steel work/building and installing glazing.

    Iím having a single storey extension built that has a feature of two sets of sliding doors meeting at an external corner, providing the ability to have them both open. Itís not a cantilevered fully open corner, the plan is to have a fairly slight steel corner post.

    The builders arrived and looked more closely at the structural layout and calcs, and saw the steels and the steel corner post are on the internal block work. They mentioned it wasnít normally like this. I have no experience of this so hadnít even considered such a thing.

    A bit of googling later and most sliding doors I see to seem to be fitted to the outside brickwork. Now I guess I could still fit the windows to the outside brickwork but I donít see how Iíd be able to work the door handles because theyíd essentially be hidden behind the vertical steel post thatís on the inside blockwork in that corner.

    If the windows are fitted beneath the steels on the inner course, the blockwork cavity would be outside so would somehow have to be sealed up without causing thermal bridging and damp issues. So I donít see how that would work.

    Is there anyone that has experience or is in the trade and could share some wisdom here before the builders arrive on Monday?

    Thanks

  2. #2
    In my experience, Iíd put significantly more weight on the views of a solid, experienced builder if they diverged from that of the engineering firm - at the very least relay the concerns to the engineers and ask for fresh eyes to double check the layout and calcs.

  3. #3
    I would of expected the steels above the doors to be wider than the post ,maybe thereís a plate welded to the under side to make them nearly 300mm wide .
    The post would probably have a plate maybe 300mmsq top and bottom.
    The post would be on the inside of the building and the doors would be on the outside course,then on the external corner your door company would supply there own post to fit between the 2 doors.
    Hope that makes sense .


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  4. #4
    I the post is to be on the external course ,the door company can just fix to that and clad it in the same materials has the doors,itís probably been done this way to reduce the thickness of the corner to give the impression of a full glass corner.


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  5. #5
    Master reggie747's Avatar
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    The simplest thing to do would be to have the "builders" and the guy who designed the extension, your draughtsman/architect get it together over a brew. He can then explain in black and white what he's proposing and they can then get a handle on it.
    As has been stated by mk1974, there will be a need to likely weld a continuous plate along the RSJ base to form a "booted or garage" lintel to allow the external skin to sit on and the door framing to sit below this. He also stated that the corner joining position of what I assume to be aluminium frames, will need a corner post also to close to.

  6. #6
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    Quote Originally Posted by tz-uk73 View Post
    and saw the steels and the steel corner post are on the internal block work.
    Surely the steels need to be the width of both the internal and external wall to support the overhead bricks.

    The vertical post can be on the inner wall only aslong as it supports the steels adequately.

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  7. #7
    Grand Master Dave+63's Avatar
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    Quote Originally Posted by reggie747 View Post
    He also stated that the corner joining position of what I assume to be aluminium frames, will need a corner post also to close to.
    As the doors are perpendicular to each other, they can close to each other without an additional post.

    A thinner, more decorative post in the corner can support the end of both beams and the relatively light weight roof. As has been mentioned though, thought has to go into supporting the outer beam.

    Iím sure the architect/designer has considered all these factors and it is just a matter of conveying it to the builder in a way he understands.

    Iím sure, as mentioned above, that a site visit and a brew will have everyone on the same page.

  8. #8
    Master reggie747's Avatar
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    Quote Originally Posted by Dave+63 View Post
    As the doors are perpendicular to each other, they can close to each other without an additional post.
    Perhaps so but one of the frames will need a receiving profile whether that's attached to a vertical steel or to the other door set (which may not be the best aesthetically)

  9. #9
    Thanks for the comments so far. I should have explained they are floor to ceiling windows at 2.7m so no blockwork or masonary above them if that changes anything.

    Also, no architect involved Iím afraid. Itís permitted development so just outline drawings that the structural engineer built his designs/layouts from.

    I have a few things Iím working on that show what I think the issue or my options to be. Iíll drop these images in this afternoon when completed.

    Thanks

  10. #10
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    I design plenty of extensions and new builds with this arrangement. My engineer and I always put the post in the cavity which makes the masonry easy and ensures the post is on the centreline of the foundation. Additionally it allows 50mm or so on the outside of the post to install some insulation (plus trim to match frame) to prevent a cold bridge between the door frames.

    Depending on the door frame thickness and fixing detail, sometimes tabs are welded to the post so that its position relative to the cavity can be tweaked. It is definitely not good practice to fit the frame to the inner leaf and try to somehow seal the cavity.
    Last edited by benny.c; 22nd November 2020 at 13:15.

  11. #11
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    Quote Originally Posted by tz-uk73 View Post
    Thanks for the comments so far. I should have explained they are floor to ceiling windows at 2.7m so no blockwork or masonary above them if that changes anything.
    There will be the roof structure and weight of tiles etc to consider, so it is possible that the horizontal steel beam could be along one wall but not both, however it's an unorthodox solution.

    I think pics would definitely help

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  12. #12
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    Quote Originally Posted by benny.c View Post
    I design plenty of extensions and new builds with this arrangement. My engineer and I always put the post in the cavity which makes the masonry easy and ensures the post is on the centreline of the foundation. Additionally it allows 50mm or so on the outside of the post to install some insulation (plus trim to match frame) to prevent a cold bridge between the door frames.

    Depending on the door frame thickness and fixing detail, sometimes tabs are welded to the post so that itís position relative to the cavity can be tweaked. It is definitely not good practice to fit the frame to the inner leaf and try to somehow seal the cavity.
    In my experience this is the correct way to install the steel work, the frames can over lap the post by 10 to 20 mm. The void can then be insulated and clad over. Installing the steel on the inner cavity has has no advantage. Engineers like to see the load above carried centrally so centre of the cavity is optimal

  13. #13
    2.7m high, floor to ceiling windows and youíre happy to go forward with some free advice from a forum and your builders are starting tomorrow? Have you submitted the building regulations application? Has the structural engineer completed the SAP calcs to show the extension will meet Part L? There are myriad questions that flow from there, answers to which will have a bearing on whether your extension will turn out like you hope.

    Quote Originally Posted by tz-uk73 View Post
    Thanks for the comments so far. I should have explained they are floor to ceiling windows at 2.7m so no blockwork or masonary above them if that changes anything.

    Also, no architect involved Iím afraid. Itís permitted development so just outline drawings that the structural engineer built his designs/layouts from.

    I have a few things Iím working on that show what I think the issue or my options to be. Iíll drop these images in this afternoon when completed.

    Thanks

  14. #14
    These are the structural drawings. The extension is the 7.3m x 5.3m box at the back. You can see the two steels both c.5m long off a 120mm square corner post thats on the inner brickwork.



    The builder has asked i pay a building regs chap from London Building Company so building regs will i believe be covered, along with visits and sign off at 5 or 6 stages.

    I did employ an architect who did us a lovely set of drawings for a larger build right across the back of the house, did us building reg drawings, got me planning permission, and sap calcs but when i got building quotes, all were 100% more than budget. So having spent c.£5k on the architect and fees etc i wasn't very excited to do all that again. Therefore decided to go permitted development route, giving us flexibility in design, but obviously i recognised the importance of structural engineer and commissioned that.

    You are right on the sap calcs though, i need to check that with the builder if he has that covered. The previous full planning permission was ok because a lot of the windows being replaced were old single glazed units, anyway whatever they did that got it to work.

  15. #15
    If it cant stay as it is, my thnking is it'll need to change to something like one of the following options



    looking something like this from outside with teh doors having their own floating corner





    or could leave steels on the inner course and fit the windows to the outer course like this, and just move teh corner post along say 60cm to enable access to the door handles



    with steels looking something like this






    or perhaps all the steel work moves to the outer course and the windows sit beneath them and fix to the steel corner post


  16. #16
    Master
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    Put the steel in the cavity.

    I assume you’ve submitted a Prior Approval application for larger extensions as that won’t fall under regular PD rights? And also assume it’s more than 2m away from your boundary?

  17. #17
    Quote Originally Posted by benny.c View Post
    Put the steel in the cavity.

    I assume youíve submitted a Prior Approval application for larger extensions as that wonít fall under regular PD rights? And also assume itís more than 2m away from your boundary?
    Hi, yes prior approval submitted and neighbours consulted and local authority said can go ahead. Itís about 1.9m from fence line

  18. #18
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    Your roof is going to be too high for PD (3m max at eaves within 2m of boundary) assuming the following:

    150mm to DPC
    2,700mm to ceiling
    220mm joists
    120mm insulation (assuming warm roof)

    Total 3,190mm (and that excludes falls on the roof which will add say 100mm min)

    You could do a cold roof in lieu of warm roof and drop your slab to less 150mm above ground but neither is ideal.
    Last edited by benny.c; 22nd November 2020 at 14:53.

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