Is it concrete or wood deck.

The footings on the deck are per today's code we live in ct the deck is wood which would get repurposed.

Would like this so that I can use it for family dinners we usually have 15 people need a bigger space plus would be a great room to entertain and sit to see the beautiful sunsets

As mentioned what is code for a deck is not code for living space get a pro before you end up having to rip it all out.

You need a professional contractor. Sounds like you want to add an additional, not a sunroom.

If you're in CT, this is going to be VERY expensive. Be sure your house and neighborhood are worthy of the expense.

Did you end up getting some professional quotes for this? We'd like to convert a screened porch into a 4 season room next year. I haven't gotten quotes yet but want to have a starting point/reference to understand how much to save for.

I have not but have been told to use $75-100 per square foot. We are looking at 24x24 room

I think you would get better quotes if you just said you want to remove an existing deck and build a 24'x24' addition to your house. The construction techniques for a deck vs. a 4 season room are so much different that you will probably not reuse anything you already have. A deck only has footings and floor construction that are adequate to hold up a deck, and it will not be acceptable as the basis for construction of a one story structure. Even the wood in the existing deck is unlikely to be of any use for constructing the new addition.

Bruce

Yes that makes sense.

I completely agree with Bruce! The effort to somehow retrofit the deck won’t be worth it and you may pay extra for someone to try to jury-rig and still end up with a substandard result. Start over and do the job right (from the foundation up). Then you get complete flexibility to get what you want, maybe 24x24 or maybe a somewhat different size. FWIW, building costs are pretty high right now. The cost of materials is high due to all the natural disasters and alll the tariffs (even my roofer says his supplies are creeping up, due to the tariffs). Don’t forget to budget for permits too.

Others have touched on the inadequacies of deck framing to support walls, windows, roof, etc. I'd also be concerned that this is going to be hands down the coldest room in the house if you try and convert the deck to a conditioned living space. It's New England, I don't think it matters how much insulation you jam up under there. It hurts to demo a three year old deck, but it the long run you're better off starting fresh from the ground up with something designed for the purpose you want.