Engage a local architect.

See if you can get a contractor to give you some kind of idea where you could be going with cost first. Does the house have a sloped roof? Adding into an inside corner like you show is difficult due to roof pitches.

Thanks for the response. The addition isn't going into a corner, I think you're confusing the pool/patio with a structure. The addition is just going at the end of an L-shaped house. The roof there is a simple pitch sloping towards the east and west. Seems like it should be a simple addition structure-wise.

Hi, Ben,

I concur with Seabornman. If you want to get informed input regarding costs, check with a couple of local remodelers. They purchase construction materials and trade labor as a regular part of their day job. Any cost estimate you'd get from an architect would be at least one level removed. Further, an architect's estimate would be based on historical costs for similar projects. With the supply chain issues we're dealing with due to covid-19 using historical costs to estimate current costs will most likely produce an unpleasant "surprise" at some point in the process.

400K-800K worth of work won’t be recoupable. Even in a “forever” home. Work within your footprint or move.

400K-800K? What are you talking about?

I agree with Charles and Seaborman. I always tell clients to get three quotes. Don’t choose the cheapest either. If you feel good with one then engage them to help and check reviews.
And Celadon, what???? That’s insane no it wouldn’t be that much!

Math. It adds up. And 2021 is likely to be at least 20% higher.

https://www.remodeling.hw.net/cost-vs-value/2020/

Not in your area, but friends added a bedroom and bathroom back of the house and it was nowhere near the numbers quoted around usually in the forum. Somewhere around 150 to 175/sqft. Costs are very local...

What's the age of your propery?

bought a (smaller) ranch in 2014, with an intetion to add (we added just 200 sq feet). U-shaped. Alliowed us to add a big master bathroom, master closet, etc.

But. Built in 1968 or 1970..things add up. Asbestos remediation. It's okay to have asbestos-it's not ok to disturb it once remodeling. Asbestos was practially everywhere.

Whatever you move/reconfigure/touch..flooring-needs to be redone.

HVAC-all new HVAC.

Plumbing-was already easier to do all new plumbing (didn't move things around, added them, yes)

. Was no insulation in the house, at all-all new insulation.

Roof-had to be partially redone.

New kitchen..

Electrical had to be added, etc.

Sounds a lot like your project. (unless you choose to do just one out of three things. we also thought we'd do addition only. didn't work that way. it starts 'creeping", once you open the walls etc)

Then backyard had to be at least partially redone(we took a break, 'cause whole story took us two years. Tackled it only last year. Nothing fancy, except I did go for a nce tile, to keep in character with the house)

While remodeling we saved tons of money by hunting vintage/open box..but not time or nerves.

It's So Cal here-so to add plans, permissions, 6 inspections, huge dumpster, port-a-potty on premises(the port-a potty company were the ones always on time lol. The smoothiest part of remodel.)...

The house was 1675,sq f and became 1875 sq feet. Nothing special. Was a modest ranch in nice area, stayed a modest ranch in nice area. More congruent with itself than it was.

Partially closed off kitchen, added closets, didn't move structural walls. Did splurge on some custom tile and custom cabinetry given kitchen is pretty small.

So..I don't know about 800K. But if I'm honest with myself.(and I really dont want to be, lol) .it can be 400K. Everything together, Depending on whether you choose to do all three, and your local costs, and what does it entail in YOUR house,

Our contract was cost plus type.

I agree to start with people who build homes in your area. Get several opinions. To get the idea.

We had several opinions -and they were almost all pretty much similar ballpark. we chose by chemistry, and willingness of GC s to even deal with us/our project. Not everyone wants dealing with additions unless they're fairly easy additions only. Where no or minimum remediation involved, no other things inside, etc,

I must add that the best part of our remodel , after all, was the addition. it's so seamless nobody can't find it, nobody who even knows the story. Nobody remembers that's why we started remodeling in the first place,

but it turned to bedown to studs remodel, and it was more complicated than bullding new, I think.

The money won't be recoupable (even though the prices right now are crazily up-but that's the market..nothing to do with our remodel. remodel adds value of course, just maybe a half of what we spent. On a good day.)

Time and nerves..for sure not recoupable.

It might be still worth it, the learning curve, you'll get for sure. And maybe better home for your family, both in terms needs and wants,

Having written all that long post..your house can be younger, with less problems, less surprises.., you might decide on smaller project out of three, etc, etc.

Do use pros if decided to move forward-whether architect, or designer..we didn't, wanted to save money...I acted as my own designer (with DH's help of course), and it was 24/7 job. Exhausting.

Unfortunately I found these forums when I was well into remodel already. Use them too.

ETA: sorry for the typos

I'm in South FL and we're on some land so we see neighbors doing extensions around here. Are you in an HOA and allowed to add on? Celadon always throws out big numbers like that, so unrealistic and seems to like to shock people when it's not necessary.

In your layout I wouldn't add the 3rd bathroom, seems unnecessary when there is another bathroom right there, I'd just work with that one and expand it into the pool closet area and move the pool closet or get rid of it. That'll save you $. Definitely get a few quotes from contractors and try to ask around and get referrals.

An architect is trained to work with you on navigating the process and developing and coordinating all the elements, not just drawing up the plans. Contractors and builders build according to your documents.

If you are confused about the process as a first time homebuilding patron, you might consider starting with Kickstart House (www.kickstarthouse.com), which is a homeowner support community that offers resources and coaches you on how to be an informed and empowered homeowner.

There's a free checklist download here: freeguide.kickstarthouse.com