how to stiffen up bouncy victorian terraced timber floor ?

[gentlegreen]

Evening all .

I'm finally getting to grips with my ancient peasant dwelling (insanely, though I've nearly paid off the mortgage, I couldn't afford it now even though my salary is 3 times what it was when I bought it 22 years ago) ....

I've just stripped out the floor boards from the front bedroom and the lath and plaster ceiling is landfill (that which I'm not still harbouring in the recesses of my lungs).

intention is to use tounge and groove chipboard since I will be carpeting the upstairs. (the boards were fairly knackered in any case)

Since I completely replaced the upstairs ceilings , I was all set to replace the joists and set them in steel hangars, but I now see the beam ends are sound and the timber quite likely better quality than I could buy ... so I started thinking about bracing with additional timber ..... and thence to some sort of steel bracketing ... even expanding cement to secure the beam ends. But then it occured to me that if the ends were too firmly anchored to the walls, then flexing of the beams would likely cause cracking ?

Am I barking up the worng tree as it were ?

thanks for your indulgence :-)

.

[Chris Bacon]

Make sure the joists are sitting properly. Bolt timber or steel to the joists.

[gentlegreen]

OK, so I build a beautifully rigid raft ... would the ideal fixings be rubber expansion joints ?

.

[Chris Bacon]

Not sure what they do be, I'm el farid.

[gentlegreen]

I suppose it's due to once owning a Norton Commando with rubber mounted engine, and later aspired to Harley Davidson ownership ....

I also have neoprene expansion joints in my lead roof valley.

I was wondering if it might be a good idea to open up the joist pockets and inject rubber into the void instead of cement .....

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[Richard Faulkner]

In message , gentlegreen writes

In a few rooms in my house I had an engineer have a look and, whilst he said that there was no real problem, (structurally), he specified steel beams fixed below the ceiling in the room below, and ramped hard against the ceiling. The floor is now solid as a rock, and soundproofing and heat insulation has improved.

[gentlegreen]

thanks, but I don't have the headroom - especially as I'm about to have new stairs fitted in reverse - with the entrance through the main supporting wall .... ... plus the steel beam ends would have to be secured on the single brick party walls ....

I'm thinking that the chipboard, plus maybe a bit of doubling up of extra beams should make the floor sufficiently rigid. My main concern is whether the (stiffened) floor should actually be rigidly connected to the (lime mortar) walls at all ...... and whether the two systems of different expansion coefficients (composite wooden beam and walls) shouldn't have an engineered expansion joint as opposed to the informal slippage of beam ends against brickwork ...

. .

[Chris Bacon]

They're mountings, not expansion joints!

Is that a valley gutter? Why "neoplene expansion joints"?

As long as they're seated properly, just strengthen the joists. Are any excessively notched?

[gentlegreen]

well ...call it poetic licence :-)

My Norton had the early shimmed "isolastics" so they were never brilliantly adjusted and it had a rather funky "gentle tank slapper" at 31mph :-)

New regs dictated that I either went for this option, or had the whole roof rebuilt with 6 steps in place of the original 2. If they fail while I'm still living there I'll get a "cowboy" to lay plain lead. Here again, the original timbers - though gently dished on the south-facing slope, are probably better than new timber - and the original clay pan tiles are perfectly adequate in combination with modern membrane.

Over the years various contractors have been a bit free and easy - I'll probably bash in some tapered plugs while I'm at it ... It was reading that it's now compulsory to use hangars in new build that set me wondering if that would be such a good idea in an old structure.

.

[Chris Bacon]

Those things did have a reputation...

Amazing! Lead in roofwork has been around for a Long Time. Neoprene has been around for... 60 years (guess), and in roofing for ? years, and "New Regs Now Dictate". It's flabbergasting.

[meow2222]

also fitting a row or 2 of accurately fitting noggins improves rigidity. So does screwing the chip floor to the beams every 6" to create a stressed box construction.

I'm not a struc eng, but I nkow that anchoring floor timbers to brick walls is used as a method to control wall movement on old houses. So it must be ok to do it.

NT

[The Natural Philosopher]

If you are just stiffening, there is no need to attach the stiffeners to the walls at all.

Just double up the joists by bolting the new ones to the old. Or nailing, but bolts can be better..or use three bolts and plenty of nails..but nailing to an old lath and plaster ceiling may mean no plaster..

A bouncy beam is well below failure, and the largest bending moment is in the middle. Just stiffening the middle half of the beam will do nearly all you need actually.

If its possible, you should increase floor DEPTH by using deeper reinforcement than the original beams, if the raise in floor height is not a problem.

Finally, you should use cross bracing between the joists - top of one to bottom of next - to further stiffen the stricture. 2" x 1" is enough here, nailed on.

I think the modern standards for up to a 4 meter span is 6x3 joists at

400 centers herringboned.

But someone else here will know better..

[The Natural Philosopher]

It will help - its a stressed skin/I-beam sort of thing, but joist doubling is the starting point, and deeper if you can.

I think the attention to the OLD joist mountings is a red herring. Whatever you choose will work. And no need to make NEW joist mountings for the new joists - just bolt new hard to existing at the ends.

The herring bone bracing really makes a difference. More so than the chipboard cladding. In effect it creates another 'beam' at right angles to the normal run of the joists, spreading the load applied over one joist to adjacent ones. It MUST be crossed though, so loads always place one of a pair of crosses in compression, or the lot will just shake out under walking etc.

One thing I did, that makes a bit of difference to noise, is to shove

12mm fibre board strips under the chipboard over the joists. This allows takeup of slight height variations, and as little bit of sound deadening. Not huge, but not much material is needed so its cheap.

Also, for best non creak finish, glue the chip T&G together, and seal at the wall edges with a mastic - I use decorators caulk..its amazing how much noise can travel through a small slit.

[Chris Bacon]

He's taken the L&P ceiling down, so re-inforcement will be easier!

[gentlegreen]

Herringbone straps sound delightfully high tech - I will certainly be pusuing this. There are currently noggins at the half way point.

[Cicero]

Coach bolts seem to work a bit better if you add these between the timbers:

[The Natural Philosopher]

00 centers herringboned.

consuming but dead easy to do..Noggins sort of work, but have to nbe accurately cit and nailed at top AND bottom,

[The Natural Philosopher]

Yes. I've got those too.Really stop the stuff shifting around they do.

[Rob Morley]

Wouldn't it be a lot more effective to screw ply to the underside?

[gentlegreen]

Steel it is then :-)

I was pulling lath nails earlier and trying to put myself into the heads of the builders. I noticed the noggins aren't actually central, but central to the chimmney breast so the last one could help support the flagstone grate. And the joists themselves - could almost have been cut from one tree .. with one or two under-sized - therefore needing a batten to keep the ceiling horizontal .....

Were the plaster ceilings standard in those days, or would they have been fitted later ?

I think I'll double up every 3rd joist - using coach bolts and timber connectors, and probably 3 rows of herringbone straps.

And 50mm of rockwool for sound and thermal insulation.

thanks everyone :-)