Are you sure they are carpenter ants? Or merely the little black ants that tend to invade this time of year? The first thing I'd do would be to get a firm ID on that. You ought to be able to internet that fairly closely without calling an exterminator first thing. That should tell you what the second step might be. Either an exterminator and an engineer, or just the engineer.

Now, wood expands and contracts with humidity, so some change in wood is NORMAL and to be expected. Not being on site, it's difficult to determine if yours is normal or not. Post a few pictures of what you're talking about here.

I would assume that a contractor would have evaluated the structure upon which he was going to build. If nothing was brought up by him I think I would call an exterminator for an evaluation and report. I would ask that he look for any structural issues. Asking the contractor about structural issues after the job is complete is likely a sure fired way to watch him go in to CYA mode.

"We had added a second floor deck right off the kitchen, steel secured into the brick outside the second floor where we also added a kitchen."

I'd begin my investigation at the flashing detail where the deck ledger meets the brick. If it's letting in water, you've created carpenter ant paradise. Been there, done that.

Where do you live ?
When was the flooring installed?
Was it properly acclimated before installation?
Was there constant temperature control (HVAC) since installation?

I live in New York City and this is a 120 year old brownstone and we left the original hardwood floors intact and just refinished them except for where we removed a wall between kitchen and dining room (and added three strips of wood where the wall had been - the island is installed in the middle of where the wall used to be - and we also installed about 10 partial strips of wood where we removed a dumbwaiter and some ducting to make the kitchen about 25" deeper which is where we placed the fridge.

here is a pic for context - there has definitely not been temperature control since installation - being an old house, it can get pretty cold in the winter and pretty hot in the warmer weather - we don't have central air, but do have centralized heating via boiler ( and thermostat placed on the parlor floor where the new kitchen is)

As for whether these are carpenter ants, I googled big black ants and found pics of carpenter ants and that is what we have. Whether they are doing anything problematic, I don't know. Another forum poster said to check where the steel deck is anchored at the bric of the house because if water is getting in, that is a perfect place for a carpenter ant infestation. So I'm going to investigate that as a priority although I don't know who might be an expert on that

It might be worth mentioning that the door to the deck used to be a window so we had a window converted to a door in addition to adding the deck... So a number of places where perhaps the changes could end up with structural issues and/or risk of new places of entry from the outside, for ants

dreamojean:

I replaced a sliding door at my home in Michigan. About 5 years later, I unzipped the vinal siding on found a huge nest of carpenter ants munching on my header. I had punctured my flashing when I replaced the door. If there were no flashing or a big gash, the damage from rain would have ruined the drywall and I would have noticed and fixed it before anything more serious happened. But a tiny puncture is much more insidious. It's not big enough to cause visible damage, but it is large enough to constantly wet the wood and the ants loved it.

This was after I replaced the header above the basement walkout, also infested with carpenter ants due to an improper flashing installation, when the deck was built before I bought the house.

When we tore out the old shower when remodeling the master bath, the idiot tile man cut the membrane instead of folding it in the corners. Again, replenishment of water but not enough to notice a leak, wet wood, and carpenter ants.

I just checked where the steel enters the brick on the NW corner of the steel deck and lo and behold, there are two quarter or larger sized holes in the brick where there isn't any flashing or other sealant - it's at a place where the kitchen is installed (it's a one-wall kitchen and that's where the hole is, near the chimney).

I'm pretty sure do a carpenter ant infestation but don't know whether that means it's creating any structural issue - I did just hire an exterminator to inspect and treat the problem entry areas BEFORE we get anything caulked - I also have been calling our contractor and will reach out to our architect or an engineer to be safe...

I just checked where the steel enters the brick on the NW corner of the steel deck and lo and behold, there are two quarter or larger sized holes in the brick where there isn't any flashing or other sealant - it's at a place where the kitchen is installed (it's a one-wall kitchen and that's where the hole is, near the chimney).

I'm pretty sure do a carpenter ant infestation but don't know whether that means it's creating any structural issue - I did just hire an exterminator to inspect and treat the problem entry areas BEFORE we get anything caulked - I also have been calling our contractor and will reach out to our architect or an engineer to be safe...