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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthormarsaday
    • CommentTimeAug 17th 2017
    Does anyone have experience of using the masonry joist hangers ?

    I decided to go for a suspended floor on my extension as it will save me putting back in approx 15 T in materials. I thought carrying 10 lengths of timber up the drive would be a bit easier than pushing barrowful of materials.

    Anyway i am now at the stage of building up my walls from concrete level. I have done a course in foundation blocks and a course where the telescopic vents will go. I now need to build up one breeze block level and one common concrete brick level and i should be at the level where the joist hangers will strap over.

    1) Do i just rest these hangers on the block or do i set them in a mortar first and then build up on top. OR do i screw the joist into place first by plugging and drilling the block ?

    2) How do joiners/builders get the exact level. I am a bit worried my levels will be a bit out. When you come to fit the hanger is it better to make the hanger a little higher (say 5mm) than necessary and then you notch the joist out at each end to achieve the correct level.
    • CommentAuthortony
    • CommentTimeAug 17th 2017
    Build joists into the wall or use sleeper walls on the oversite. Joist hangers can be noisy and springy
    • CommentAuthormarsaday
    • CommentTimeAug 17th 2017 edited
    I don't think you can build them into the wall any more. I have ordered the hangers now so have to take this rout. I have over sized the timber for the spans and have a small sleeper wall in the middle of the main room, so it should be quite strong.

    I have spoken to expamet and i know how these hangers sit now so all good.
    • CommentAuthorMarkyP
    • CommentTimeAug 17th 2017
    if you decide to use hangers I think it is standard to set them slightly high to allow a margin for level by notching.
    5mm doesnt sound like enough. I think there are building regs diags showing guidance for notching joists. From memory, I think at the very edge you can go up to 0.15 of joist depth.

    some of our joists were notched a good 20mm but our block layers were sloppy. I dont have Tony's experience but ours are not squeaking or moving so far.

    on a related note, if you have any metal work strapped over the joist top - hangers for trimmers and such, give the joist top a couple of swipes with the plane and keep the metal and nails just below the surface. Our joiners ignored my ask on this left me with some annoying creaking floors.
    • CommentAuthorMike1
    • CommentTimeAug 17th 2017 edited
    1) Joist hangers can rest directly on the block - no need to set them in mortar. You then need to build 3 courses of block above them and allow the mortar to cure before loading them with the joists.

    If you don't have 3 courses of blocks above - for example at doorways - then NHBC good practice is to either build the joist ends into the wall instead of using hangers, or use a trimmer to carry the load to the joists either side of the opening (using suitably sized timbers).

    2) Notch out the joist ends to make sure all the joists are level.
    • CommentAuthormarsaday
    • CommentTimeAug 17th 2017
    Thanks for the info. I have a good idea of what is required now and will be getting them in next week.
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