I modified a house with a walk out basement from Single Family into 2 units. My plan is to live in the smaller downstairs unit. I finished the upstairs renovations and now have renters in it, but the down stairs is not finished. It needs a lot of work. I've been trying to be accommodating about the process but the tent is not being cooperative so now my contractor pulled the plug because he is afraid of this Quit Enjoyment law. When I say the tenant isn't cooperative, I mean that I asked if we could work until 9 pm and her response was I want in writing what hours you plan to be working. That didn't answer my question. This is just one example of how my conversations go with them. Ugh! So frustrating. Before they even signed a lease we had several discussions about me living there. Should I just leave it until the lease is up? If I push the issue could they really sue me or something? What's the worst case scenario?
You will find your answer by studying your state landlord tenant regulations. Each state varies.
Our regulations allow tenants to file for rent rebates in cases involving reasonable enjoyment.
What does the lease say? What do your state/local laws say? What is the nature of the work? Remodeling an adjoining unit until 9 PM is pretty late in the day. You may have had discussions about living there, but I bet you didn't have discussions about air compressors, circular saws, and drywall demo.
As a side note, you should never be asking permission about your own property. If you needed to rehab this property at night, it should have been noted in the lease.
I do see both your and your tenant's POV. I'll assume you gave them ample warning before they signed the lease that construction was going to be done in the other unit.
Most areas have city ordinances for the days and timeframes when construction is allowed. I would follow whatever that is. I doubt it is as late as 9PM. For example, where I live, I think the hours are 7AM-7PM. And "construction" is a broad range of work. I used to manage the office for a tree care company and we fell under that same umbrella.
I would also talk to the tenants and find out what their typical schedule is and, to an extent, work out a reasonable schedule. For example, if a 7AM start would wake them up, agree not to start construction until 8AM. You don't have to do that, but it's courteous considering that these are people you share wall(s) with.