I'm sorry to say but 400 square feet for $15k sounds very tough. That's only $37.50/square foot and that's not counting the cost of things like permits and inspections. Most building around here starts at about $150/square foot and can go way up from there. Building costs vary widely, but I don't think they'd vary that much.

Are you DIY'ing all or any of this? If not have you talked with any local builders to get their input?

Is the window AC/heater combo instead of HVAC permissible to your local codes?

Remodeling is more expensive per square foot than new construction. Better triple your budget, and that's with no frills finishing out. Unless you DIY everything. Then, you can probably do it for around double your budget, but with a few nicer finishes.

You could do it here, but really all it'll get you is a shell of a very plain, squarish room.

I'm just going to back up the other posters. I can't imagine trying to do that.

I assume you know that a redone $20,000 kitchen is considered a modest kitchen in an existing space. But, we've seen $2,000 redos--mostly cosmetic--that really spark up a tired space.

What shape is your roof in? Is there an easy way to meld the new and old roofs or will you need to redo the entire roof? What new windows are you contemplating? Will you need any external or internal door(s)? Is landscaping a part of the project? How will you handle the ceiling treatment? Are you buying new appliances? Are you hoping to match a floor? Is there any impact with cost implications for the existing house room(s)? How easy is the plumbing access? the drain and hood venting? the sewer and gas connections? Are there any materials matching issues, such as woodwork? Are you planning to add more money to the pot at a later date or is this the max you can spend?

Do you harbor any dreams, illusions, or strong hopes that will interfere with strict adherence to modest- to low-cost goals?

Don't neglect to budget for the unseen costs: e.g. One thing we did not budget for in our DIY project is the cost of renting equipment, such as shingle stapler and floor nailer and dolly. Don't forget cost of building permit. Plan a minimum of 10% and more like 25% for surprises.

Look for local advice. Go talk to a couple contractors and your State ag. extension agent if there's one.

When my husband and I met with an architect recently about a possible addition, the architect estimated $200/sq. ft. for just the room (with good quality flooring, painted walls, etc.). He said we might be able to do $150/sq. ft. if we went with cheaper flooring and chose some other less expensive materials.

It doesn't sound like this is a DIY, so I think it would cost much more than $15K.

That said, if it were DIY, you could probably just about make it work.

DH and I are going to be putting a 24x24 attached garage on our house in the late winter/early spring, and we have costed it out and will be able to do it for just about $15K. That's paying someone else to dig he foundation and pour the concrete. We'll do everything else ourselves. Fortunately we will not have to pay to rent any tools because we already own all that we'll need. Oh, and we already have two windows that we'll be removing from the family room to use in the garage, and we have to two 9' garage doors and two openers.

I'm sure you know this, but if you change the footprint of the house, and add heated/cooled space, you have to pull permits. If you don't, you won't be able to sell or refi your house. Especially in the South, you can get away with a lot of DIY that technically you should have a permit for (plumbing, electrical, etc.), but not an addition.

It cost us most of that to finish out an existing space (attic) that was not as large. The only change to the roof was to put in a dormer for a window and was done at the same time the rest of the roof had to be replaced anyway (didn't pass inspection when we bought it). There was some framing inside, drywall and electrical work. We had to move and AC/furnace unit a few feet and relocate/replace a water heater with a similar move.