Wow, that is a lot to do. Here are ballpark points to consider. Ask around in your area to see what they will cost.

Scope of the job to include:
Design of new space by architect (for permits)
Approval of design by structural engineer (for permits)
Stamp by engineer required for building permit
Cost of building permits and inspections.
Complete tear out of existing space and debris removal costs
Excavate and pour new foundation that will support 2 story space
Upgrade electrical panel to support new wiring for space. Includes electrician costs, fixture/parts cost/ inspection costs.
Upgrade plumbing to support new space Includes plumber costs, fixture/parts cost/ inspection costs.
Upgrade heating and cooling to support new space. Include equipment costs, ducting and gas/electrical parts cost/ installation costs/inspection costs.
Cost of materials for actual space, flooring, wall studs, wallboard, ceiling, fixtures, appliances, insulation, roofing trusses, roof shingles, windows, doors, hardware, paint.
Labor
Unplanned extra expenses (10-15% in reserve of total of all above)

My ballpartk guess, (just my opinion) based on work we did several years ago on our home that is 80 years old, in a midwestern city, would be that you would spend between $80,000 and $180,000 based on labor costs, permitting and design costs, and the level of finishes that you select, as well as how much work you do yourselves.

To do everything on this list is 6-7 months. But you aren't torn up for the first 2 months.

Anyone else?

Thanks so much for the "to do" list. I actually have a friend who is an architect, so that might help us out. It's a rowhouse, so it's not as though we can do any complicated curves or other designs on the structural walls. We want to do as much of the work ourselves as we can, but neither of us is willing to work with electricity. We're OK with plumbing, but given that the house was owner-rehabbed before and not done very well, I'd rather pay a professional to get it straight. We were hoping that we could move the tub into the house before the extension is built because we want a nice clawfoot, which will be impossible to get down the stairs. But all the interior design we can take care of. I'm an artist and have many plans for the interior.

Don't forget the locale differential in pricing. You are in a urban area, which adds to the expense. You are located on the coast, not in the cheaper heartland. You are located near one of the most expenwive cities in the country to live. I'd expect your estimates would be at least double of what julie gave you because of these factors. It could even be more if the building is older and will need structural issues addressed before any new construction can begin or if you are dealing with historical registry issues.

Make a list of materials/finishes on the projects that you want to d.i.y. Then get estimates from reputable trades people in your area that you would be considering for the projects you can't do or dont have time for. Add these numbers up and tag on 25% and that will get you a ballpark. Unexpected costs, such as finding things in walls when you open them up will rise as the project is running along with delays such as scheduling conflicts, back ordering of materials, even weather.

Is there an existing home that has most of what you want?

I'm guessing you could move with less expense and certainly with less disruption. This will consume at least a year of your lives.

Will this actually increase the value of your home? Will it increase by as much as you'll spend on the improvements?

HUGE regional differences, so impossible to even get close.

But if you want a point of reference, we did something remotely related, taking the back of our house from this:

To this:

We hired a GC to build the shell for around $46K total, and we finished the entire inside (insulation, drywall, electrical, tile, trim) for another $10K I think. No plumbing. Shell took about 2 months to build. Total 500 new square feet. The "turrets" are about 10x10.

We took about 4 months to get the design done exactly how we wanted so we'd avoid changes mid-construction. I highly recommend that.

Weedyacres,

Gorgeous renovation!

You said 'we finished the entire inside (insulation, drywall, electrical, tile, trim) for another $10K I think.'

Do you mean you did that work yourself or you had someone do it for 10k?

TIA

At least 100k. And if work is heating up where you are, it probably won't be helpful to finding a willing contractor if you are doing part of the work yourself. If I were you, I would drop by John Stevens, have a crabcake sandwich and a beer or two, and see if they know any good contractors. (Even if they don't, it's still worth the visit.) :)

Organic: "We finished" means DIY (except drywall--Weedy doesn't do drywall), so that $10K is the cost of materials.

We did a two-story addition in Central Pennsylvania that cost us around $95,000. We tore down a one-story side of our house to the ground and rebuilt as a two-story. I attached the whole thread of our progress.

Here is a link that might be useful: our addition