Sagging floors fix & the neighbours

[Daisy87]

Hi all

We’re starting a renovation on our flat in North London - a two-bed Victorian converted into flats in the 70s. We own the leasehold and a share of the freehold.

Our main issue’s the floors. The living room’s about 6 × 4.5 m, and the timber joists span the long way with roughly 6 cm of sag in the middle. Turns out a load-bearing wall underneath was removed years ago by some cowboy builder. Same story in our flat, so the ceiling mirrors the dip.

Almost worse is the noise from upstairs - both airborne and impact. We’ve lived in old London places before, but this is wild. It’s like living in a drum . You also get a really good sense of the general tone of each conversation upstairs.

We’re planning to strengthen the floor and ceiling and improve soundproofing by sistering the joists and adding insulation while everything’s open. Since we’ll be lifting floors and dropping ceilings anyway, it seems the time to do it right.

Question is, can this be done entirely from our side, or would the flats above and below need to be disturbed too? And at what point does deflection become bad enough for Building Control to get involved?

We’re hoping to get our fellow freeholders on board by making this as easy on them as possible, but we’d like to be prepared in case there’s any resistance.

Grateful for any thoughts or first-hand experience - always good to hear how others have tackled the same mess.

 

[Cubist]

Ordinarily when an internal wall, particularly one that rises through two storeys of a building is removed, new bearer beams or RSJ steels would be installed to carry the ceiling/floor joists in each of the storeys. Is there any evidence - maybe a boxed in section under the ceilings - above where the wall would have originally stood? What I think needs to be established before considering any solution is what and how the joists in the floors/ceilings are currently being carried/supported.

 

[Daisy87]

In the flat below, the new ceiling’s been dropped and boxed in for spotlights, so it’s hard to tell whether they might have hidden a beam in there.

The structural engineer who’s had an initial look (without opening anything up) suspects there isn’t any support though. We’ll know more once we’ve spoken with the neighbour, but for now we’re trying to get our case together before breaking the news to them.

Above our flat there’s definitely nothing - the ceiling looks like it’s just new plasterboard fixed straight onto the sagging joists. Someone, more recently by the looks of it, even went to the trouble of getting the coving to follow the bow in the ceiling .

According to the engineer, the joists are only bearing on the party walls at either end.

 

[Cubist]

According to the engineer, the joists are only bearing on the party walls at either end.

Presumably you mean the walls either side of the 4 metre run/width of your lounge?

 

[Daisy87]

Unfortunately not - the building’s about six metres wide, and the joists run the full span. We think they were originally meant to cover roughly 4.2 m and 1.8 m, with a load-bearing wall in between.

 

[phillc]

Presumably you mean the walls either side of the 4 metre run/width of your lounge?

No, he said the joists run in the direction that spans 6.5 metres.

I assume the SE has created your design for sistering the joists etc?

Can this be done without disturbing upstairs and downstairs? Well, if you intend to correct the sag, no. As sure as eggs is eggs they'll have decorated, run coving, etc. to go with the sag, as has happened in your flat.

If you're just trying to prevent the sag getting any worse, then I guess it depends on what your SE has designed. If they're sistering the joists with something that is significantly less than the depth of the joists (or, in your ceiling, sits below the joists in your room) and if you get lucky with how your neighbour's services run in your floor and ceiling voids, you might be ok.

But, as you'll be doing structural work on a shared freehold I assume you need their permission anyway, and I'd err on the side of it being disruptive ...

 

[Daisy87]

Thanks so much for your input!

The SE’s come up with a design that involves doubling up the existing joists with new ones of the same size, but he seems to assume the joists can be jacked up from both above and below. We can’t quite picture how that would work in practice - especially from above. Have you ever done this or seen it done?

As for movement, the flat upstairs might be fine; they’ve got what looks like old carpet over original floorboards, which I imagine can take a fair bit of remedial warping (right?).

Below, though, as you said, it looks like a lot of effort went into creating and decorating a new (suspended) ceiling just last year. It actually looks dead level, so we can't imagine it moving two inches or more in the middle without cracking to bits.

I just can't face the thought of asking them to re-do this

 

[phillc]

Jacking up normally involves acros from below ... Maybe your SE has a cunning plan?

Also, does your SE *know for sure* that you have continuous joists along that span? If there was originally an intermediate load bearing wall, I can't see why the original builders wouldn't have just put in 3.5m-ish joists ending over the wall. Overlapping ends may well have been nailed, but the sag you are seeing would be scissoring of that in large part.

I'd struggle to see how a simple sistering scheme could solve that; surely any SE would do the obvious and say steels.on padstones?

Steels on padstones will defo disturb upstairs and downstairs and will also need party wall ageeements with all the left and right neighbours.

But I'm just guessing. I'd challenge your SE on whether they know or have assumed your joist setup tho ...

 

[Cubist]

Has your SE come forward with any views concerning the width and depth dimensions of the extant joists? Is the sag you see in your floor immediately above the old wall and where the two joist runs would likely meet? Does your SE know whether the joist runs that were supported by the now removed were ever capable of meeting head on? If they don't, which is most likely, a sistered solution is unlikely to work.

Also, is it safe to assume the flat below yours is on the ground floor and has solid - not suspended wooden - floors? Or is there another flat or basement below that storey?

The method for corrective work would have to mean that the ceiling in the flat below yours is opened, at least partially, to allow the introduction of at least two acrow type props/jacks to first level your floor and allow insertion of strengthening timbers/steels to support your it. Before doing the same in your flat to lift your upstairs neighbours floor WHILE leaving the acrow props in place in the neighbours flat below yours.

 

[Daisy87]

The flat below’s a maisonette - ground and first floor. Both levels have been reconfigured, but on the ground floor there do seem to be boxed-in beams where the old walls once were. The first floor’s beams situation is uncertain. We’re on the second, with another flat above us.

The joist setup so far is an educated guess: the structural engineer lifted a bit of carpet, noted the direction of the floorboards (running perpendicular to the long span), and poked a bit of metal in to gauge the void. That’s all we’ve got to go on so far.

We were really hoping you’d say, “Of course this can be done from above, we do it all the time!”

Lifting the floorboards and opening up the ceiling next week with our builder and the engineer - will report back!

 

[Cubist]

Good luck. I hope you find that the old joists do meet and that a sistering approach is possible despite my doubts.