After a year the "Who is responsible?" is probably you.

brickeyee - That's not really helpful. I'm not asking either to fix the problem at no cost. If it happened after 6 months, who would you say is responsible? Who do I need to contact to make sure that there isn't a bigger problem.

First of all, you need to put a 4' level over the island in all directions and see if it's still level. Then do the same for the flooring around the island. This will tell you how much the house has settled and in what direction. That will impact any repairs that might need to be done.

If the floors have settled substantially, then there's your issue. If the floors are level, but the counter is not, then it's a cabinet issue. Cabinets have to be perfectly level, with support underneath the stone all the way around. If you found the counter to not be level, look at it's support and where it has cracked. Look at the underside of the stone with a straight edge to see if there are any problems with it being flat and fully in contact with the cabinet bases. If you have an overhang, what supports it? What supports the support? How is that weight transferred from the overhang down to the floor and foundation? A couple of accent corbels on the thin back of a cabinet are not sufficient.

You may just need your countertop fabricator to come back out and do an epoxy repair of the stone, or you may need the island to be re-leveled or overhang re-engineered, or in extreme cases, you may need to assess the addition's structural integrity. But, start at home yourself to see what you can figure out so you can see what the next step might be.

And yes, after 4 years, any repairs will be on your nickel unless there was something egregious like the addition doesn't have proper foundations or something. Even then, you'd have to sue the contractor, spending thousands of dollars on your own lawyer. Even if the repair involved rebuilding the additions's foundations, it would still be cheaper to pay for it with another contractor than to try to take the first one to court.

Did your contractor bring in the installer or did you? I would probably go straight to the installer, but if you didn't have any relationship with them I'd go to the GC and have him contact them.

Livewire posted some good questions.

Although I have granite, not marble, I had fabricator install steel rods to support our counter. I was told if we didn't have the rods it might crack

Live wire - Thank you so much! It's been about 15 months. I brought in the installer because he came highly recommended on this forum in the NE, however, I was less than impressed. I'll do some sleuthing on my own before calling the installer or contractor.

All good advice-what type of marble do you have? Does the crack run along a fissure in the stone. If it is just on the edge it could just be a fissure that was open and not noticed or something new. If it doesnt appear to be caused by settling than have a stone refinisher look at it and fill with a clear glue such as a thin cyanoacrylate/super glue(using a clear glue will retain its natural look and fill the crack)
which may stop it from opening more.It is a small job so you may want to consider having him or her refinish the island or do some other work to cover the minimum charge.
Stu Rosen
www.mbstonecare.com
www.stoneshine.com