Depends. If you're a bank appraiser, then we often hear them say that they value square footage among like properties. So, they would look for comps for a daylight basement home among those recent sales that also had daylight basements. Similarly, a two story home would have comps of other two story homes. If you're a Buyer, most Buyers seem to have a preference for the potentially higher ceilings and additional light that a two story home would have over a daylight basement style. But, often daylight basement homes are built that way to take advantage of a view. We have so few data points, that it's often hard to distinguish between the various factors. I don't see people using any kind of formula re: how they value daylight basement space. Best thing to do in answer to your question is either a market analysis of comparable properties (CMA) or have an appraiser complete an appraisal.
Jill Schuster, Principal Broker, Town & Country Realty, 541-619-5427 direct.