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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthordelprado
    • CommentTimeMar 6th 2017
     
    Can anyone tell me if putting structural ply down either side of the joist helps at all?
  1.  
    In order to stiffen joist you need to increase depth. Increasing thickness (sister joists) is a very inefficient way (in terms of effective use of materials) of stiffening joists but has the advantage of not increasing the depth of existing structures.

    So to answer the question - Yes - but you will need to glue and screw the ply to the joists. However it would probably be better to glue and screw a batten of structural timber to one side of the joist (one side only needed). If you have access to the underside then this might be easier as there are no implications for door thresholds.

    IMO there is no advantage in using ply over timber. In fact timber might be better than ply and OSB won't work.
  2.  
    Posted By: Peter_in_HungaryHowever it would probably be better to glue and screw a batten of structural timber to one side of the joist (one side only needed)
    That's what I would do and don't use dog tooth fittings either - also make sure the screws are clean (ie no thread) for pretty much all of the depth of the wood you fit to ensure clamping effect and glue strength optimisation - remember the screws won't be doing much work afterwards their purpose is to clamp tight the new wood over the full face. It will make a big difference and I wouldn't stress about getting right to the ends if it were difficult. TBH pretty much any bit of wood of any decent length and any depth/width (except OSB) will make a dramatic difference!
    • CommentAuthorMikC
    • CommentTimeMar 6th 2017
     
    +1 ☝


    50% of the wood fibers in a piece of ply will be aligned in the wrong direction to help with the bending stresses of the joist, better to use good quality timber with a high C rating C 24 for example. Full Face glueing of one joist to the other would be stronger than dog tooth washers and bolts IMO.
    •  
      CommentAuthorfostertom
    • CommentTimeMar 6th 2017
     
    Posted By: MikCFull Face glueing of one joist to the other
    sounds ideal but often difficult/ineffective with old, non-flat, painted/coated or deeply-dirty existing timbers.

    Am I the only one who finds the low-frequency bounce of an old floor quite charming, involving, compared to the high-strung rigidity that the industrialised world has enforced on us?
    • CommentAuthorGotanewlife
    • CommentTimeMar 6th 2017 edited
     
    Posted By: fostertomoften difficult/ineffective with old, non-flat, painted/coated or deeply-dirty existing timbers.
    That's why you use buble glue:bigsmile: - obviously not as good as mating 2 perfectly flat and clean wood faces together but still as effective as any other solution for old painted bent wood.
    Posted By: fostertomAm I the only one who finds the low-frequency bounce of an old floor quite charming, involving, compared to the high-strung rigidity that the industrialised world has enforced on us?
    Well I like my floating bamboo laminate on 4 mm of sound absorbing underlay - a 'soft' effect but without the wider concerns/issues of an old floor.
    •  
      CommentAuthorfostertom
    • CommentTimeMar 6th 2017
     
    Posted By: GotanewlifeThat's why you use buble gluehttp:///newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif" alt=":bigsmile:" title=":bigsmile:" >- obviously not as good as mating 2 perfectly flat and clean wood faces together but still as effective as any other solution for old painted bent wood.
    Oh, surely - copes with inch-scale knobbliness/deviation? And bond only as good as old paint's adhesion?
    • CommentAuthorPeterStarck
    • CommentTimeMar 6th 2017 edited
     
    Posted By: fostertomAm I the only one who finds the low-frequency bounce of an old floor quite charming, involving, compared to the high-strung rigidity that the industrialised world has enforced on us?


    I don't know but I certainly prefer a floor to be rigid and feel rigid. I dislike intensely staying in old hotels where the floors slope and are uneven. My first house was a 17th C cottage, complete with deathwatch beetle, with uneven sloping floors, never again.
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