How can I get my indoor covered "sleeping porch" added to the square feet of my house

[Thomas Bennett]

I own two duplex properties in a neighborhood in Virginia that commonly has indoor covered "sleeping porches". I noticed on the appraisals that the square feet of these porches are not part of the calculation of the appraisal because they are not considered appropriate living spaces due to lack of heating and cooling though they are fully inclosed with windows(not screens like a normal porch). Does anyone know if additions can be done such as insulation with the addition of a heating and cooling system in order to get the space added to the appraisal? For example, on my most recent duplex bought for $270/sqft, the indoor covered porch is 136 sqft. If this space was added than that could be an increase of $36,720. Im wondering if anyone has done this and how much they were given per square foot for this addition? (e.g. full value of $270/sqft or a lower value such as half or $135/sqft). I don't think this would cost much to make the additions so could be a significant way to force appreciation if re-appraised at close to the full value.