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I Joists & metalwork


matthyde83
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We’re just about to install I Joists for our first floor.  “Under no circumstances notch the flanges”.  How does this work with metalwork and plasterboard getting a nice flat finish?  The hangers will protrude down at edges (and we have some meeting in middle on a steel) even a few mm can cause issues with the plasterboard.  Same issue for the restraint straps with the floor?

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IMO a couple of mm will not cause problems in either case. Plasterboard and flooring is flexible enough to cope with any deformation of that small amount. In engineering terms it would not be acceptable with steel which is not that flexible. In my floors upstairs the boards were fixed with d4 glue and no nails or screws and that fills any small voids anyway.

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26 minutes ago, joe90 said:

IMO a couple of mm will not cause problems in either case. Plasterboard and flooring is flexible enough to cope with any deformation of that small amount. In engineering terms it would not be acceptable with steel which is not that flexible. In my floors upstairs the boards were fixed with d4 glue and no nails or screws and that fills any small voids anyway.


My builder thinks it will cause screws to pop etc in plasterboard.  Traditional joists he would usually recess the hangers… 🤷🏻‍♂️

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7 minutes ago, matthyde83 said:


My builder thinks it will cause screws to pop etc in plasterboard.  Traditional joists he would usually recess the hangers… 🤷🏻‍♂️

Then your only option is to use counter battens of some sort or hardboard strips along all joists!!! (nowhere on my build has any screws popped). Others will be along shortly with their input, @nod ?

Edited by joe90
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1 hour ago, joe90 said:

Then your only option is to use counter battens of some sort or hardboard strips along all joists!!! (nowhere on my build has any screws popped). Others will be along shortly with their input, @nod ?

Spot on Joe

Counter baton with rough cut 75x25 mil 

Also save bogging out 

ECE104F0-85C2-4147-B030-5318695C4C7E.jpeg

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Next question is sealing around the ends... I've seen the Tony tray method and mentioned to builder but he is really worried about the strength if we're taking plastic through the blockwork in two places.  Also seen end caps but cannot seem to find them readily available anywhere!  Any other methods/ideas?

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6 minutes ago, matthyde83 said:

That’s kinda where my head is at…

Great minds think alike 👍, it needs to be thin and flexible . I worry (like your builder) about building in “slip plains” ?

Edited by joe90
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10 minutes ago, joe90 said:

Great minds think alike 👍, it needs to be thin and flexible . I worry (like your builder) about building in “slip plains” ?


Yep so if it’s at least around the joists only it would avoid that.  I’m thinking of present wrapping the ends in say roof membrane 

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3 minutes ago, matthyde83 said:


Yep so if it’s at least around the joists only it would avoid that.  I’m thinking of present wrapping the ends in say roof membrane 

Yes, staple it tight to the ends a bit big, build it into the wall then afterwards unstable it,  glue/pin it to the wall about an inch only and plaster over it to create an airtight barrier.

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