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Neighbour's new patio doors causing cracks?

Anonymous user 23/02/2024 - 2.38 PM

Our neighbours put in a new kitchen about 3 years ago, and put patio doors into the back wall of the outrigger of their Victorian house, the outrigger shared with our own in a long terrace. We've been told that under the foundation is normal for a Victorian house, with sandstone probably 3-6 feet under the surface of the ground. Since their patio doors have gone in, small cracks have appeared above their doors, and above our own patio doors (both internal and external leafs), which have been in place for over 15 years I think, and are also in the back wall of the house. I estimate there's about 4 feet of supporting wall between the patio doors, and another 3 feet of supporting wall to each side to the outrigger corners. Our patio doors have a substantial steel plate lintel, theirs is a concrete one (I presume reinforced). Since their construction, their new plaster (dot and dab I think) has 2 vertical hairline cracks on the party wall about 10 feet back into the 18 foot outrigger, whereas our solid plaster wall is fine. There is also a first floor crack opened up on both sides of the party wall where the outrigger joins the main house, but no cracks anywhere else, i.e. on the outer walls of the whole outrigger. There are what I think are large supporting wooden beams the hold up the back wall of main part of the house, and there are hairline cracks under both of these, and a few hairline cracks following the panels in our plasterboard kitchen ceiling (in the outrigger of course). The rest of the building is tickety-boo. Should I be worried? Is it just minor settlement of the building, or is their lintel not up to the job and is causing movement in the outrigger? I assume they and their builder used a correctly sized lintel and got building regs, but I don't know. I know we don't have building regs for our patio doors (we got an insurance policy as our surveyor picked it up), but you can see our steel plate (5 mm thick I think) above our door. I presume we are not liable for any remediation if any is needed. Am I right? I'm guessing the chain of liability is the builder, then the neighbour's insurance, then our own? Advice very much welcome! ----- Follow-up: Dear Mike, Thanks for the answer. The cracking is vertical rather than being stepped, and doesn't appear to be there in the attic or on the outer leaves of the outrigger. Surely those extra cracks would be there if it were structural? But anyway, what you say sounds sensible. I doubt if my neighbours would pay for a structural engineer's calculations though.