Keep looking. It's a major PROJECT. THERE IS NO SUCH THING as "just" add a floor : ) Beyond that, assuming you have the resources, nobody can answer your question here, It's a function of structural support , window location and much, much more

If you need advice? Walk an architect through the house you are considering. This isn't the forum for the question.

This is not the house for you.

You said one of your "needs" was a 2 story great room. And yet you would take that out for the safety of one of your children.

I admire the willingness to sacrifice your need for your child's safety. But that just means this is not the house for you.

Edited to Add: I stand corrected (see below). I missed that the need was for NO two story great room.

It's still not the house for you, if you need to do all of that work.

The need is for NO two-story great room.

nobody reads lol...........

Thank you everyone :) Definitely a large endeavor than I thought. This market is so wild. Hopefully more houses open soon with less bidding wars.

 Have a great weekend everyone!

No, its not commonly done.

In addition to structural supports to the foundation, you will need to modify the HVAC system and provide windows that meet the building code for natural ventilation (unless you provide mechanical ventilation to the entire house).

If the house really checks all of your boxes, change the railing to a higher wall. It doesn't need to go to the ceiling. Or have it go to the ceiling and put non-operable windows at the top if you need light to get to the hallway. Taking out a railing and adding a wall is probably less expensive than doing the reverse, and way less expensive than changing the great room to only one story. I know it's difficult to find a house these days, so maybe this is worth doing for you. Even if you don't have this issue I think two story rooms with overlooks are a pain - all of the hot air rises and makes the second floor difficult to cool in the summer, so this change wouldn't negatively affect the resale value from my perspective. Some people may feel differently, but not everyone will.

I've done a frameless tempered glass "cover" over guard rails. Hard to climb and let's light through. Can be removed by a future owner.

I agree with kandrewspa. If this house fits your needs, otherwise, then remove that railing, and add a full wall there. I dont have little ones anymore, but, if I ever bought a house with a railing like that, I would definitely replace the railing with a wall. I really dislike those railings they put up now days.

This is a crazy housing market. How soon do you need to move? If there is no immediate need, then just keep looking. Get your realtor to do all the work.

If it is an immediate need, then most of your needs may have to be good enough with an alteration. I would not even think of doing a floor - cost prohibitive. A railing can be changed to a wall or made higher to discourage being climbed on - that will also help with some of the sound.

If you want more ideas, post a picture if you have one.

Best of luck in your search!

My three sons were fond of climbing to the second floor on the two inches of stairs on the open side of the railings/balusters. (One now enjoys bull-riding and demo derbies!). Maybe rule out a two-storey house period.

https://palmercustombuilders.com/home-remodeling/floor-over-two-story-family-room-or-foyer/

https://www.houzz.com/discussions/3148877/closing-in-an-open-2-story-foyer

More commonly done than you likely think.

"Maybe rule out a two-storey house period."

Walking on two inches of stairs builds character. When I was growing up, ours was 7/8".