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Housing - New Build: Scaffolding setup for build with joists fixed to a ledger

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  1.  
    • CommentAuthorNeilD
    • CommentTimeMar 14th 2018
     
    Hi all,

    First post on here - been lurking for a while picking up lots of useful info - very grateful for collective wisdom.

    Just about to start a new build - large detached house, cavity wall construction, aiming for close to passive standards.

    The plan is to fix first floor joists to a ledger plate bolted to the block work with resin anchors a la 'The Green Building Store' cavity builds. Our brickie is suggesting we will need full scaffolding inside and out as the blocks will need at least a week to go off before fixing the plate. I am curious if others have had to do this or have managed a workaround by carefully scheduling elements of the block work which was my suggestion - there is a garage and internal walls to be getting on with whilst the blockwork to be fixed to goes off.

    Thanks
    • CommentAuthortony
    • CommentTimeMar 14th 2018
     
    Build them in and use a “tony tray” to sort the air tightness
    •  
      CommentAuthordjh
    • CommentTimeMar 14th 2018
     
    Posted By: NeilDThe plan is to fix first floor joists to a ledger plate bolted to the block work with resin anchors a la 'The Green Building Store' cavity builds. Our brickie is suggesting we will need full scaffolding inside and out as the blocks will need at least a week to go off before fixing the plate. I am curious if others have had to do this or have managed a workaround by carefully scheduling elements of the block work which was my suggestion - there is a garage and internal walls to be getting on with whilst the blockwork to be fixed to goes off.

    Silly question, but have you asked GBS what they did?

    I'm not sure what the scaffolding is for - to build the walls or to attach the ledger or to attach the joists? If one of the last two, you may find that a moveable tower is as useful as fixed scaffolding. Also, you won't need full strength in the walls to attach the ledger, or even to attach the joists, perhaps, but only when you start loading the floor.

    Where's your airtightness barrier?
    • CommentAuthorgyrogear
    • CommentTimeMar 14th 2018
     
    Posted By: NeilDThe plan is to fix first floor joists to a ledger plate bolted to the block work with resin anchors


    I am not a SE, but in my part of the world this would be a renovation approach.
    For a new build, the joists would be pocketed in, but a composite floor (steel tray, mesh and concrete) would be laid on top, and connected into the wall.
    Multiple builder's stays to support the joists while all this is going on.

    gg
    • CommentAuthorrevor
    • CommentTimeMar 15th 2018
     
    Could you not use joist hangers built into the blockwork. If you are concerned about cold bridging I guess you will get some of that through the ledger anchors anyway. You say you are only doing a close to passive house standard. I set my joists in the blocks and sealed around the joint with the block with acrylic sealant.
    • CommentAuthorNeilD
    • CommentTimeMar 15th 2018 edited
     
    Thanks for the replies;

    Tony, we could go with a Tony tray as an alternative, I have several of the threads on the pros and cons of different approaches. The main thing that puts me off the Tony tray is the extra slip planes in the structure - particular since wind load will be high in our location.

    djh; I will have to ask GBH. In terms of what the internal scaffolding is for I guess predominantly to stop there being a huge drop into the building for the brickies as the walls are being built up above first floor level without a first floor. Will definitely be looking into purchasing a movable tower - will come in very handy for many jobs I'm sure. Airtight barrier would be a membrane behind the ledger plastered into wet plaster.

    gyrogear: I know it's not a common approach but I believe several other on the forum have used it. I would be really interested to hear first hand experiences from them.

    Revor: I understand the evidence suggests joist hangers are just as leaky as built in joists.
    •  
      CommentAuthordjh
    • CommentTimeMar 15th 2018
     
    Posted By: NeilDIn terms of what the internal scaffolding is for I guess predominantly to stop there being a huge drop into the building for the brickies as the walls are being built up above first floor level without a first floor. Will definitely be looking into purchasing a movable tower - will come in very handy for many jobs I'm sure. Airtight barrier would be a membrane behind the ledger plastered into wet plaster.

    Hmm, in some estate-built developments I've seen recently, they filled the inside of the house with large inflatable cushions, which were presumably to reduce the consequences of falling from heights. It might be worth looking into to see if they can be hired as a cheaper alternative. I hired a tower when we needed it (maybe three weeks total during our build). We have a membrane behind our ledgers too, I just used an offcut of DPM and double-sided butyl tape patches around the bolt holes to seal the penetrations.

    Fortunately, we didn't have to wait for the walls to set before we could install the first floor since our structure is loadbearing as soon as it's stacked.
  8.  
    ''djh; I will have to ask GBH.''

    GBS?
    • CommentAuthorNeilD
    • CommentTimeMar 16th 2018
     
    Ha ha, yes GBS
    • CommentAuthorrevor
    • CommentTimeMar 16th 2018
     
    Air tightness depends on the quality of workmanship as much if not more than the materials or method employed. Another thought could the brickies not corbel the wall where the joists will rest with a wider block for the joist to rest on. (You may need advice on appropriate strength block) This would make a much studier stiffer construct than what you are thinking of doing as once the wet trades is done you won't have access to the securing bolts of the ledger, the timber will shrink when house is heated and you could get squeaking as ledger becomes loose and moves on its anchors.
    •  
      CommentAuthordjh
    • CommentTimeMar 16th 2018
     
    Posted By: revorAnother thought could the brickies not corbel the wall where the joists will rest with a wider block for the joist to rest on.

    How would you detail the airtightness? Then see the discussion above.

    once the wet trades is done you won't have access to the securing bolts of the ledger

    I don't understand that?

    the timber will shrink when house is heated and you could get squeaking as ledger becomes loose and moves on its anchors.

    Ledgers have been around for a long time; I haven't heard of this problem. I expect using dry timber is part of the answer.
    • CommentAuthorNeilD
    • CommentTimeMar 17th 2018
     
    Definitely agree about quality of workmanship Revor. I think if I follow you with the wide block corbelling idea the the blocks would require steel in them to support the shear load from joists and I don't follow where the air barrier would run - doesn't sound like an easy solution to me.

    Maybe the approach I am suggesting isn't that common at all but I haven't heard of any issues from those that have done it. Maybe I will run the Tony tray by my SE but given the number of windposts he has just specified due to the altitude, exposure and proximity to the coast I can't imagine he'll be keen but I could be wrong.
    • CommentAuthorrevor
    • CommentTimeMar 17th 2018
     
    I am struggling to understand I think how you are doing the air barrier. If you cannot make inset joist hangers air tight or go around corbels ( which do not necessarily need to be full length along the wall they could be cut to length concrete lintels sticking out at the spacing of the joists) how are you going to seal around window and door reveals?
    •  
      CommentAuthordjh
    • CommentTimeMar 17th 2018
     
    Posted By: revorI am struggling to understand I think how you are doing the air barrier.

    The air barrier is very simple, it's just a piece of plastic sheet behind the ledger that is plastered into the plaster that forms the bulk of the airtightness barrier. That's an awful lot simpler and less prone to mistakes than sealing anything every joist. The Tony tray is equally simple but has different tradeoffs.

    how are you going to seal around window and door reveals?

    Completely different problem. Windows and doors do not project through the airtightness barrier, nor do they recur as many times as joists.
    • CommentAuthorNeilD
    • CommentTimeMar 23rd 2018
     
    Just to give an update our brickie has agreed that we can probably work around without a full internal scaffold. The plan is to prioritise the inner skin where the ledger will go first then to work up the external skin, other internal walls and the garage whilst they off. I'll let you know if it works out!

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