When calculating the cost of adding an additional room to your house, a lot depends on what the space will be used for. A 10x12 kitchen or bathroom will be more expensive than a similarly-sized living space in the home as the price of fixtures and appliances tends to drive prices up. While a simple kitchen renovation, as of 2011, might run anywhere from $14,000 to $38,000, new construction cost for other rooms are usually in the $80 to $110 per square foot range.
Square Footage Costs
Labor and materials for new home construction anywhere in the United States run, as mentioned, between $80 and $110 per square foot, according to author and homebuilder Carl Heldman. From that range, you can extract a general idea of whether construction costs are toward the low or high end in your area. Assume a $95/square foot cost for this example. A 10x12 room equals 120 square feet, multiplied by $95, yields a total estimate of $11,400.
In most cases, that $11,400 estimate will likely be in the ballpark of where the actual cost falls since most room additions are essentially the same as new construction. Your add on will need a foundation, four walls, roof, electricity and probably plumbing. Remember that this estimate is based on simple construction and doesn't include any materials upgrades you decide to make. Before you drive that first nail, remember to check your local housing department to see if a permit is required for your planned construction as many municipalities regulate any type of new construction within city limits.
Anywhere you build in the country, expect the labor costs for hiring a general contractor to be about the same as the materials expense. In other words, you could half the average cost to add a 10x12 room to your house by simply doing the labor yourself, reducing the estimate from $11,400 to about $5,700. If you have the tools and skills, don't be afraid to take on the project yourself because the savings could be substantial.
With competition to make a buck in the construction industry so keen, most companies prefer to keep their cost estimates close to the vest but keep in mind there is no magical incantation preventing you from coming up with your own average cost to add onto your house. It's a simple matter of using a pen, paper and calculator to accurately estimate how much you need in the way of materials. After that, it's just basic math.