Very grateful for any opinions as DH is driving me insane very worried.
We had an extension built over two years ago. Used a great builder, very experienced. We copied a plan used elsewhere on our estate - room above the garage, kitchen extended into the garden. Work was inspected, signed off, had a structural engineer out to approve everything. Additionally, when DH bought the house new (20 years ago) he asked about the garage foundations and the builders assured him they'd made passive provision for another storey on top.
We immediately had cracks appear where the house settled around, e.g. the new steel beam. I was expecting this, DH wasn't, but the builder reassured him (they were still building at that point).
Two years on and we are still getting random hairline cracks appear everywhere. DH is now convinced that the garage foundations aren't strong enough and it's falling sideways and taking the side of the house with it. Every day he asks me to inspect some new crack that he's spotted (usually one that has been there for a while), or opine on whether an old one is getting longer or wider.
From my perspective: none of the cracks are wider than a few mm, most are hairline and less than 1mm thick; we've had the heating on a lot more (and at a higher temp) due to WFH; most of the cracks appeared within the first 12 months after the build; extensive Googling says don't worry unless the cracks are very wide; I've seen subsidence on properties before and that included wide cracks in the exterior wall that you could fit fingers or coins into and this isn't it; none of the other houses on the estate seem to have a problem (and thanks to lockdown we walk past them every day).
From DH perspective: none of these cracks appeared until after the extension; they're all clustered around the stairs / old exterior wall / new room above the garage / new kitchen roof (which has a massive glass lantern in it); we are still getting new cracks over two years later.
I can't seem to reason with him - and this anxiety predates the pandemic, although it's definitely getting worse. It's got to the stage that I'm tempted to pay for a structural engineer to have a look and put his mind at rest even though I think it will be a massive waste of money.
Is there anyone with experience of this stuff (structural, not relationships!) who can advise please? Should I be worried about this?