There are basically two ways to estimate costs. You can use square footage and estimate cost per square foot, or you can work up costs from each line item in a construction budget. I did both.
Before I explain each, let me state the obvious. There is no upper limit on what a house can cost. If your house has a $100,000 photovoltaic system in it, that adds $100,000 to the cost of a house without that system. If you put 4000 sq-ft of antique wormy chestnut flooring in the house at $25/sq-ft that will cost $100,000, or about $60,000 more than nice oak flooring, and about $80,000 more than carpeting. Most of this post will relate the basic costs of building a high-quality structure, and not to the expensive jewels you might place in or on that structure.
Caveats: “market conditions” and “sweat equity.”
Estimates Based on Square Footage
Bigger houses will cost less per square foot than smaller houses. These costs are pretty good estimates for a house 3000-5000 square feet.
Custom home 3000-5000 sq-ft built by professionals…pretty much can’t do for less than $100/sq-ft. Plenty of homes are $500/sq-ft. I believe my actual construction costs will come out to about $133/sq-ft not including any design, engineering, or surveying costs (the costs you incur before you break ground). Everything, including all soft costs will probably come out to $150/sq-ft. Unless you are obsessive about cost management, I believe you should assume you will do worse than that, probably closer to $200/sq-ft. Most architects consider $200/sq-ft a low budget for a custom home.
What’s in square footage? All enclosed areas including garage, finished basement, and storage. All covered decks and patios. Mine does not include a large terrace, which has a foundation, pavers, and an awning that is 8 ft. deep.
Bank’s cost worksheet
Some good rules of thumb I used, and which proved to be pretty accurate in 2010:
Windows and patio doors cost $300-400 per unit, where a unit is an individual sheet of glass in a frame.
Interior doors are $200-400 per unit, depending on whether they are painted 6’8″ doors or finished wood 7′ doors.
Appliances: make a list…get quotes from usappliance.com.
Framing $7-10/sq-ft of floor space, not including materials.
Foundation $200/cubic-yard of concrete placed.
Excavation: could be as low as $10k for a flat lot with a crawl space or $60k for a steep wooded lot with full basement.
Fire protection (sprinklers): $1-2/sq-ft
Lighting fixtures: very little to a lot
Lighting controls: $0 to a lot
Tile: $10/sq-ft for installation