Bouncy floor - sistering joists

Postby TOMPARKER44 » Wed Apr 11, 2012 7:20 pm

Good evening all,

I have had a good look online and on this forum for what I want to know and have found some useful information but still have some gaps that I hope people can help me with.


It is currently a bedroom on the 1st floor in a Vicorian house and measures 3.4m x 2.8m. The joists are 6" x 2" spaced with 400mm centres. When I walk on the floor it bounces and the handles on the wardrobe wobble, when my 2 year old daughter (it's her bedroom) runs and jumps around it sounds like she is going to fall through the floor when downstairs!

I am in the process of splitting this room in half with a stud wall and create a bathroom and bedroom. A heated floor with porcalean tiles for the flooring.

1) I will be carrying out the work this Friday
2) Sister the existing joists with 1 x 6 " x 2"
3) Which ever mechanical fixing method chosen glue will be used
4) 12mm plywood on top of the floor boards

1) M12 square head bolts, square washers & timber joiners or 6.5 80mm Joist Screws?
2) Will shuttering ply suffice, I can PVA it if need be?
3) Is it worth using joist hangers and if so can I still sister the joists?
4) Slightly off topic - will I need to strip the lath & plaster off the existing external walls when tiling?

Thank you for your time

Posts: 3
Joined: Wed Apr 11, 2012 6:43 pm


Simply Build It

Postby welsh brickie » Sun Apr 15, 2012 9:17 am

you have probably finished now,but if you havent,joist hangers are fine,use dog washers on the bolts to bite into the timbers.
You dont need 12mm osb board use 6mm ply on the floor screwed and glued.
The lath&plaster wall you can dryline with plasterboard and drywall adhesive if its solid.
welsh brickie
Posts: 2157
Joined: Sat Apr 12, 2008 7:54 am

Postby TOMPARKER44 » Mon Apr 16, 2012 7:46 am

Hi Welsh Brickie,

thank you for the reply.

I haven't finished it yet as it didn't go to plan! For some reason I decided to get 6" x 1" and rip it down to 5" x 1" and put one either side of the joist but the bolts I had weren't long enough and the wood was a bit wet as it had been outside (treated kick boards).

I have realised that the grade of wood used for kickboards probably won't be as high as that of joists so I will be buying 6" x 2" joists and ripping down to 5" x 2".

I did have 6mm ply but took it back and bought 12mm shuttering ply instead as may screw this directly to the joists and chuck the floor boards - what are your thoughts on this? If I do this then I can put 12mm shuttering ply straight on the floor boards on the landing and it should bring it to the same height as the bathrrom floor (ply + tiles).

Cheers - Tom
Posts: 3
Joined: Wed Apr 11, 2012 6:43 pm

Postby welsh brickie » Wed Apr 18, 2012 2:05 pm

dont use shuttering ply.If you dont want to use existing floorboards,use T&G chipboard flooring they interlock and glue the joints.Its a much better floor.
welsh brickie
Posts: 2157
Joined: Sat Apr 12, 2008 7:54 am

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