Can you better explain the fastening type?

It is a system that uses a slotted cutout (skeleton key hole) in a plate with a screw that is driven into the newel post. The screw is inserted into the bottom center of the newel post with the head sticking out. The head of the screw is inserted into the slot on the plate screwed to the floor.

My last choice of attaching newel post especially on a second story level For I have yet to see one hold tight for long.

No way those plates would meet code for a deck railing, I have to imagine the rules are similar inside. The easiest way to achieve the code requirements is to bolt the newel into both the joist and sill, there are lots of other ways to get there. Some surface attachment that depends on a couple of screws and a lag bolt into end grain is really unlikely to accomplish it.

Call your builder.

That system might work for a post supporting a stair railing at a turn, but not a second floor "guard". The IRC requires the top of any point along a guard or handrail to resist a point load of 200 lbs. Imagine the post were attached to a wall as a horizontal cantilever and a 200 lb person stood on the end of it.

Unfortunately, the contractor's warranty period may have expired but a good contractor should be willing to correct a design error that created a hazard.

I hope a new post can be attached from below without disturbing your house too much.

Thank you all for your input! This makes me so mad... ! We are now 2 months past our 1 year warranty period and the builder has not responded to our messages thus far. Fingers crossed.

My parents had something like that. It was never sturdy enough. Luckily there was a sofa in front of it. They eventually replaced with wrought iron that was anchored by way of 6 long bolts that went into the joists on one end and 4 into joist and 2 into wall on other end.

Is this a builder's tract house or a custom home on land you own?

It might be worth a pointed question to your town's building department why they approved that attachment method-- it probably won't do you any good, but might help the next person. Given that it is a real safety concern your inspector should have paid more attention to it.

Don't ask a "pointed question" of a building official that might suggest the department "approved" the attachment method or otherwise imply that the department is responsible for the mistake. It's the property owner who is responsible for code compliance and the building department does its best to catch what errors they can without relieving the owner of that responsibility.

Of course, the owner contracted with a builder to meet the code and can hold the builder responsible for non-compliance and errors as set forth in the construction contract.

If an owner wants the building department's help, they should just ask for it but understand that the department cannot give legal advice and an order to repair a hazardous condition would be addressed to the owner.

Still waiting on the question of whether this is a builder's house in a tract subdivision, or a custom home on property owned by the OP.

We can guess the answer by how the railing is designed and installed...

Our home was built on a lot in our Builder's subdivision-- we bought the lot from the builder just prior to the start of construction and had a second closing upon completion. The Builder did send a carpenter over this morning. He looked at the railing system and said that the piece that holds the four screws that secure the newel post was installed wrong and there should have been some screws that went in diagonally, which weren't put it. He said once it was done correctly, it will be solid and shouldn't loosen (which, obviously, I question). I asked him why they wouldn't attach it to the joist, which seems like the most secure method, and he said "This is the system we use in all of our homes and we have no problem." Not exactly a great answer... Pretty frustrating.

Famous last words from builders:

1. We always do it this way and we've never had a problem.

2. There's nothing to worry about.

Famous last words from architects:

1. Sure, the builder can do this...no problem.

2. You've always wanted a large do-dad? Let's put one right over here. It won't cost that much.

OK, "pointed question" was the wrong term. I guess I view the building department and inspector as my ally in insuring that things get done correctly, even when I'm doing the work myself. They certainly can't see everything. If builders in their jurisdiction are "always using" a method that is very unlikely to meet a safety-related code requirement it should be useful to alert them to that so that they can incorporate checking that among the things that they prioritize in inspections. I'd hope they would welcome such feedback.

If it turns out that are choosing to allow a substandard system then my question might become more pointed. I know it is ultimately the owner's responsibility, but most owners, to be honest, don't have a clue, and rely on their builders and inspectors to do the right thing. Third parties who do have a clue can be an important component in keeping the whole system honest and working.

"most owners, to be honest, don't have a clue, and rely on their builders and inspectors to do the right thing. Third parties who do have a clue can be an important component in keeping the whole system honest and working."

That's true. If a homeowner wants a knowledgable person to protect their interests during construction without a potential conflict of interest or competing allegiance, it is necessary to hire such a person.