Bouncing Floor Joists

[Darren Chamberlain]

Hi,

All my floor joist bounce but after recently rearranging my bedroom the joist next the wall is now getting walked on more and is bouncing. I have tried glueing and screwing plywood to it but no joy. There is a 60mm gap between the joist and the wall, the joist is over a patio door.

See video before ceiling removed..

My question is, can i fill the 60mm gap with timber and bolt at intervals into the brick to stop the joist bouncing?

I look forward to some suggestions.

Many thanks,

Darren.

PS Access from the top is not possible.

 

[JohnD]

how long are the joists, and what are their dimensions?

Please show how they are supported by the walls at each end, and if the ends have any movement when the floor is bouncing.

Show any cuts or notches for pipes or cables

Has a downstairs wall been removed?

How old is the house?

 

[Darren Chamberlain]

Hi, Thanks for the reply.

The house is 1960 Build.
No downstairs wall has been removed.
The beam sits on a full brick either side with no movement when bouncing.
I sistered the beam with 18mm ply (only on one side as the other cannot be accessed) and it had no effect.
There is only x2 small cut outs for pipes.
The beam is 3.4m 7x2.
I have updated pictures in post to show both ends and a wider shot.

My plan is to put wedges between the beam and the wall and then resin anchor some threaded bar into brick and bolt joist to wall to stop movement. However as this is above the patio door
I don't know if that is possible.

Many thanks.

 

[Darren Chamberlain]

also....the small piece of ply screwed to the underside is stopping the bounce a little as the bounce got worse when the plasterboard ceiling was removed.

 

[Deleted member 174758]

TBH 18mm plywood for sistering will add naff all rigidity to a joist. In general you need to double up the joist and bolt it to the sistering timber at 600mm (or less) centres, which would mean pocketing into the brickwork at each end. I think however that it is overkill

3.4 metres (11.5ft) on a 7 x 2 is within tolerance for 400mm/16in joist centres for C16 timber (although it is a bit undersize for 24in centres), but you"ve stated removing the plasterboard has made things worse, so in your case i think I'd rather install some solid strutting (7 x 2 - same size as the existing) across the centre line of the room from one side to the other. Solid strutting can be installed from beneath and needs to be a tight fit to make it work. It must be the same cross section as the existing joists - 18mm plywood will not suffice. Nail it in place (3 or 4 nsils at each end of the timber blocks). Do e correctly the strutting reduces the tendency for the individual joists to twist under load (which is what causes bounciness) by transferring that twisting load into the adjoining joists. In other words it stiffens the entire floor). Attempting to fix through the last joist into the adjoining wall.structure will potentially encourage moisture to migrate into the joist which will result in premature rot and failure - and that"s why we leave the gap between the wall and the first joist in the first place!

 

[Darren Chamberlain]

Hi JobAndKnock,

Many thanks for your reply.

The room is 7m in length and the main issue is the joists don't sit square so trying to get s timber strut inserted tight down the centre line will be difficult. What about herringbone timber or metal x bracing?

Also, I'm only really bothered about the bounce on the first joist. Bill bolting it through into only the internal course of brick still potentially cause a damp issue?

Many thanks.

 

[Deleted member 174758]

Joists sometimes warp in service as they dry out - you just have to cut the blocking at a slight angle to get it in (measure the gap poxtop and bottom). I have done just that many hundreds of times over the years. Even if you don't do the whole floor i think you'd need to block between 3 and 5 or so joists to get the necessary stiffness. Installing herringbone bracing (or the metal equivalent) normally requires that both the floor and ceiling are out - the timber stuff needs space to swing a hammer from sbove and below to install it, the metal stuff generally wraps over the top and bottom of the joists and is nailed into the edges. Personally, all i know from ling experience that solid strutting is both easier and faster to retro fit

As to tying the first joist to the wall, i've already given the reasons why a competent tradesman shouldn't do this. IMHO it is a bodge job which can result in expensive repairs being required down the line and may not give you the additional stiffness you require in any case. Persist in doing it at your own peril!