Bouncing living room floor.

[Derek G.]

WE live in a house built in 1976 and the front room floor has grown ever more bouncy over the years, the effect has become quite sick-making.

About 4 years ago we got a joiner to go under the floor to fasten the chipboard floor down onto the joists and the joists down onto the sleeper wall.

But still it bounced.

Then SWMBO got pigged off with the mess and having no carpet, so the problem was put on a back burner.

Now I want to attack the problem one more time before I die.

Last time a kind gent on here suggested this was a symptom of rot in the joist ends but the house is bone dry under the floor and I have found no rot anywhere else.

Any other suggestions please as to what may be wrong and what to do about it, before I rip up the floor and stiffen up everything under the floor with extra sleeper walls, bigger joists, and bloody great nails?

Derek G.

This Looks like Finito Ruperto.

[Harry Bloomfield]

Derek G. brought next idea :

No need to go to that extreme :')

Just find out where the centre of the bounce is and check what is underneath. Maybe the supports have slipped out - just refit them and make certain they can't slip back out. Basically have someone bounce on the floor and you look to see why it is moving.

[The Natural Philosopher]

I had this once in a cottage, and thought I had rotted joists, but in fact they were just slipping off the sleeper thingies. Or so the electrician who rewired (and fixed it) said.

I think you have to pull the floor up anyway.

If the joist ends are not supported then fix that. Otherwise herringbone the joists.

[Phil L]

If you are certain that there is no rot at the joist ends, then it could be that the joists have warped upwards and are no longer sitting on the walls, but TBH, it's probably the joist ends, don't assume that they aren't rotted just because the rest of it is dry

If it's not the joist ends, and there are gaps 'twixt joist and walls, they'll need to be packed - don't use wooden wedges for this as they won't last 3 weeks, mix some strong sand/cement, about 3:1 and get some slates, or tiles and hammer them home under each joist, then splodge on some mortar to stop them 'walking'. You'll need to do this where each joist crosses the wall(s).

If it's the joist ends (which I'm 90% certain that it is), they'll need to be cut back about 3ft back from the rot and the hole widened in the brickwork so that you can attatch another joist of the same thickness and it'll need to be about a foot longer, where you join the two together, build a small stack of bricks underneath the joint so that both (the old and the new) joists are supported.

You'll need a roll of DPC, use this between wall and joist, also, wrap the new joist ends with it.

You need ventillation under the floor, which is why the ends have (probably) rotted, two 8X6 airbricks at each elevation is the norm, if these are already in place and working correctly, the sleeper walls may be solid and thus stopping crossflow ventilation, if this is the case, you'll need to remove a few bricks here and there in each one

[Zapp Brannigan]

slips of 6mm plywood buttered with glue are handy for gradual packing.

[John Rumm]

Well its either that, or packers have dropped out that were spacing the joists from the sleeper walls.

If it is just packing, then you can pack out with slate (very good crush resistance, and thin - so you can build up levels with some degree of granularity). You can also dry pack with mortar (i.e. a strong sand cement mix, with no added water other than what is in the sand, which you ram into place with a stick etc the low water content means no shrinkage on curing). I usually wrap some DPC around the underside of the joist where its going to touch the packing - staple to either side of the joist. Just to eliminate any possiblility of the packing tracking water to the timber.

For joist ends, you can cut back to solid wood and extend the ends with new timber, with glued/screwed ply plates either side of the joist that span the join and a good foot or do wither side.

The other worthwhile trick is herringbone runs across the joists. This increases the load sharing between adjacent joists giving more stiffness in that axis that you can expect from just the floor boards. Either cut from timber in a traditional style, or using pre-made galvanised ones.

[GB]

Forgive me butting in, because I've never had to deal with a problem like this. But, thinking about it logically, if the joist ends were rotten but the packing on the sleeper walls was okay, then the floor would be springy round the outside but firm in the middle. And vice versa. Would the OP care to say where it's most springy?

[Steve Walker]

Not if there are no sleeper walls and a couple of joist in the middle of the floor have rotted ends. Then the boards and the rotted joists would be being supported from the sound joists either side and you'd have a pretty good trampoline!

SteveW

[GB]

Hmm. I was going from the OP: "About 4 years ago we got a joiner to go under the floor to fasten the chipboard floor down onto the joists and the joists down onto the sleeper wall."

[Steve Walker]

That'll teach me to make sure I check previous posts! The OPs note on sleeper walls was snipped earlier and I responded to the section I read, forgetting what I'd read the day before.

I could argue that it was a reply to a generic bouncing floor problem rather than a specific one and of use to many more people - but it wasn't!

SteveW