Bouncy floors - double up joists?

[LuckyBenski]

My main bedroom is reasonably big at 4m x 4m. It's quite a wide span for the joists as the living room below is also that size - so the entire floor is suspended.

It's quite bouncy in the centre of the room and there's a dip of an inch or so across the span. The living room feels much more solid and that has its joists resting on two internal walls below (townhouse so garage/utility underneath).

The house overall is reasonably flimsy and built to the lightest of standards - timber frame walls which flex and move also but that's another story

I'm wondering if the floor will settle once we get all our furniture in and it's weighed down. That said, I'd like it not to bounce so much - things rattle if you jump up and down. I'm considering doubling up maybe two joists spread out across the width? Dividing the floor slab into thirds and strengthening along those lines effectively.

A) Would this add enough strength without being too invasive/impacting other areas?

B) Should I jack the floor up as level as possible before bolting the joists in?

C) Should I also double up the boundary joist that supports the exterior wall? This is a single, and I need to build some reinforcement there anyway as the PVC window is sagging too.

If this sounds like the right route then I can talk with a structural engineer for some calculations and validation. If I'm barking up the wrong tree I'll have to reconsider

 

[Hawk Tuah]

I wonder if an electrician / plumber has been drilling a few too many holes / cuts.

 

[LuckyBenski]

I wonder if an electrician / plumber has been drilling a few too many holes / cuts.

Not really, there's typically 2 holes and 1 notch in every joist. Holes carry the sockets and lighting, and the notches have the cold and hot water feeds. They're just slightly weedy little joists!

It's 1965 ish built btw, with relatively rapid construction i.e. grey blocks rather than bricks almost everywhere, and aforementioned wood frame walls.

 

[Mercenary Keyboard Warrior]

Yeah you need to get them reinforced before you get the waterbed installed

 

[ANDARIAL]

fit herring bone noggins or solid
This will reduce the `bounce`

 

[DXP55]

If you are able to do it I would.

When i built my extension it was a 15ft span and 2x9 were quoted for joists - a few years later you had to double up on some of the joists if not all and my bedroom was a bit bouncy - I also used those stainless steel noggings between each joist and added more than needed.
I would also try to jack ceiling up with planks and acro's - Odds are on if you don't do it, in a few years time you will be sitting there looking at cracks in ceiling plasterboard.

 

[LuckyBenski]

If you are able to do it I would.

When i built my extension it was a 15ft span and 2x9 were quoted for joists - a few years later you had to double up on some of the joists if not all and my bedroom was a bit bouncy - I also used those stainless steel noggings between each joist and added more than needed.
I would also try to jack ceiling up with planks and acro's - Odds are on if you don't do it, in a few years time you will be sitting there looking at cracks in ceiling plasterboard.

Thanks, yep there are a lot of cracks around corners and edges. Albeit mostly on the exterior walls where there's some interaction between floors and the wooden frame etc.

Acro props and doubling up sounds like the plan for now... have to convince my partner she can live with no ceiling in the lounge, which is currently the only half liveable room!

 

[Tony Edwards]

Thanks, yep there are a lot of cracks around corners and edges. Albeit mostly on the exterior walls where there's some interaction between floors and the wooden frame etc.

Acro props and doubling up sounds like the plan for now... have to convince my partner she can live with no ceiling in the lounge, which is currently the only half liveable room!

Please post progress pictures.

 

[LuckyBenski]

Please post progress pictures.

At the rate this house is going, I'll be lucky to get started before Christmas

 

[Tony Edwards]

At the rate this house is going, I'll be lucky to get started before Christmas

Ill be here.

 

[Tony Edwards]

There was an episode of Holmes on homes where he reinforced a bouncy floor.

Cant remember which one though.

 

[LuckyBenski]

There was an episode of Holmes on homes where he reinforced a bouncy floor.

Cant remember which one though.

Episode 8: Flimsy Floor - When a brand new kitchen addition floor buckles during a party, a "quick-fix" by the contractor fails to solve the problem. Mike Holmes secures the floor's joists, adds braces and reminds us that structure is just as important as design.

By any chance?

 

[Tony Edwards]

By any chance?

Yes could be but Im sure there was one without a beam.

 

[LuckyBenski]

Oooh, just spotted quite an inconvenient speed bump - poking around with a lifted floorboard planning some wiring. I realised there are cables running through every joist in this room.

I could reasonably pull a handful of wires out while I did the work I guess - it definitely adds complication though. Would have to re-feed 2x sockets and 2 light switches, plus the boiler, by my estimate. Still, that's doable I suppose.

I really wish I hadn't got so tangled in doing all the jobs at once here

 

[DXP55]

I have just googled this and it is quite interesting and could save you a lot of hassle
https://mellowpine.com/blog/floor-joist-blocking-and-bridging/ Read this.

I used those metal cross bracing things when i built mine as I knew the joists were a bit flimsey - I put loads in between each joist but those wooden blocks would be a good addition to strips.
Removing wire and pipes is a pain in the ass.
Another thing I would do which is off top of my head is use some of those straight galvanised metal bars Screwfix sell and screw or bolt them down middle of joist -one each side.
While you have access think of anything to strenthen the joists. You will only have one shot at it.
Even lengths of decent sized angle iron screwed or bolted on every other joist.
Also remember you will be adding more weight.

Herringbone strut

Herringbone strut - Designing Buildings - Share your construction industry knowledge. Herringbone struts are a form of cross bracing typically found between floor joists. Bracing between parallel rows of joists helps them to stay in place and prevents them from twisting.

www.designingbuildings.co.uk

My money would be on metal brackets as you can put them anywhere

 

[LuckyBenski]

Thanks, lots of learning for me in there. Blocking/bridging would certainly be less invasive than sistering joists, but I wonder if it will be as strong?

I wasn't planning on lifting too many floorboards actually, as the room is partly filled (for now), plus hassle. But I wonder if 4-5 strategically placed rows of metal brackets would get me there.

The remove wires/sister joists method isn't too onerous considering I rewired the house myself so know exactly where and how I'd need to pull and re-draw the wiring. It's just extra steps, but reasonably predictable ones.

I think with the wall insulation/vapour barrier questions I have on another thread, it may be time to ask a professional for an assessment.

 

[JBuk]

The blocking may* help but I doubt the metal herringbone struts would do anything as they really only stop the joists twisting

I replaced all the joists in one side of my attic room as they were too flimsy , they have a 4m + span , I found Some chart that gave me the correct joist sizes required for the span and i used the next sizes up, I think they ended up about 75mm wide x 175mm high - maybe something you want to do to compare with what you have as they may be on the small side

the other side of the room the joists were part of a ceiling for another room (which I didn’t want to strip,out) I ended up sistering these to strengthen and re level the floor, it’s worked out ok - although my walls are brick

if you do end up sistering then don’t jack anything up as it will sag back again once you remove the jacking , use the new joists to create a level surface


saying all that I can’t help wondering if some of the issue is with the timber walls

 

[LuckyBenski]

if you do end up sistering then don’t jack anything up as it will sag back again once you remove the jacking , use the new joists to create a level surface

Thanks, I'm definitely not sure what the end result will be of forcing the existing stuff to move, and then settle again. Do you mean let the new joists be slightly above the existing joist levels, assuming they're naturally straight? I hadn't thought of this but I suppose it can work - new joists would provide the top surface for floorboards, old joists would be the bottom surface for ceiling panels below. The ceiling in the lounge isn't terribly uneven (the ceiling of the top floor IS - that being the flat roof joists seem very uneven). It does mean I'd be sistering all the joists and not just some though, so a lot more work and definitely a floor up/remove all wiring job.

saying all that I can’t help wondering if some of the issue is with the timber walls

As much as they're, structurally speaking, nonexistent to the fabric of the house, I don't think it affects the floors. The joists run between party walls so parallel to the timber walls. I suppose if they were also brick walls the joists might be bolted in, but not 100% that is the case? What is true though is that they didn't double up the edge joist at each side of the floor which is a requirement nowadays. I was recommended to double those up by a structural engineer if I add any more weight to the structure.