Did my neighbours cause this damage? What do I do now...

[LoftyLawsuit]

So, it's a long one. I have lived here for 20 years. NC as this literally couldn't be more outing.

New neighbours 2 years ago. Previous neighbours boarded out their loft and added velux windows. No stairs, so when current neighbour bought, it was officially 1 bed.

Current neighbour instructed Bob the builder to add a dormer and stairs to create official second bedroom. I now understand this was possibly done from plans intended for pricing the job?

They told me about the works, and the builder knocked on my door Summer 2022 to say they would be starting work soon. I asked if the dormer would be attached to mine, and the builder said "Oh no, no, completely separate. There will be a gap." There isn't.

6 months later, I notice serious cracks on my side of the party wall. I'm scared. My home insurance ruled out subsidence but haven't helped beyond that. Even their legal team wouldn't help, as the "damage" on my side is minimal.

Long story short, no building regs, no plans submitted to council (permitted development but no checks through the build), fell out with their builders so had to get new ones to finish the job, had home insurance cancelled as they omitted to tell them about the build, no party wall agreement, no permission to disrupt and cover my gable end, oh and they then spent the last year trying to sell the property (as a much inflated 2 bed). I think I saw the For Sale/Sold sign switched 6 times, each never getting to exchange. The last buyers got "an indemnity policy" and even that sale never went through.

I need to establish the cause of movement, then establish if it's just settlement or if it will continue to get worse. But if I appoint a structural engineer/surveyor they won't be able to establish if next door caused this/applied the correct supports/strengthened floorboards etc, will they? Surely they need a survey, but how do I make that happen? And oh, they tell me they have "no issues" on their side... (except a few days ago the pair of them gave me different stories about having to replace a ceiling and plastering over cracks in a completely different corner of the house), and they have kindly suggested as it's an old house there will always be a bit of movement and to just plaster over it like everyone else does. Is that correct?

This is literally a nightmare. Money is v tight/I can't afford to throw money in the wrong direction. What's my next move?

You should have had a party wall agreement (PWA) even if the dormer wasn’t intended to be attached to your property.

Failing that the onus will be on you to prove that the damage has been caused by their works and to raise this through the small claims court. I’d start with a structural surveyor - this will need to be at your cost initially but can be aided to your claim. Without the PWA, where photos would have been taken before and after the works were done, it will be difficult to prove definitively that the damage was caused by their works.

We did have a PWA with our neighbours and a year after this had been concluded, after a very hot, dry summer, they insisted some fresh cracks in their kitchen ceiling were due to our previous building works. The neighbours paid for a structural engineer to look at the damage (I insisted we paid for a second) and both agreed that there was no way our works could have caused the damage to their kitchen ceiling and this was likely due to the clay soil contracting. We actually paid extra for the second surveyor to write us up a full report stating this to cover ourselves in future for that particular claim.

Honestly. I think if you live next door to someone else this can happen & you have to expect it too, particularly if there's building work carried out. I don't think it's definitive that they've caused any damage & personally I'd not worry about it
Or if you can't do that I'd speak to a solicitor, you might have one attached to your house insurance, but to be honest the house insurance aren't worried are they?
Do you have pictures before & after to post on here? The cracks etc?