Hello Aaron,
A quick way would be find out the typical cost per square foot of comparable homes that have sold recently in your area. You can call a realtor or go to websites that publish comparable sales to find out the cost per square foot. If the website doesn’t list this number directly just take the sales price and divide it by the total square footage of the house. With this number you can get a pretty good idea of what the addition will add to you home’s value based on its size.
Beside comparing the Area Comp value to your home, you may look into the the highest and lowest home from your neighborhood and compare them to your home in terms of space, differences, etc. Then you can have more comprehensive overview to how much value by addition you may add to your home.
You can check you local real estate market (zillow.com, realtor.com, mls) for comparable and multiple the average SF by the desirable addition. You can check with a real estate broker in your area.
Current value of home divide it by existing square footage; multiply answer by proposed new square footage.
It is very simple you need to go to a company or website that actually give you the value of your house or the houses in your area like Zillow like Trulia and so on and so forth then after that you need to see the comp in the area or you can see that houses next to your house it’s better to see houses at the actually have the same square footage is yours and the same amount of bedrooms and bathrooms take the square footage take the estimated price divide the estimated price with the square footage and then you’ll have how much value you have for every square foot but remember to be tricking because some houses have a lot of square foot and then the tam low does not apply
