Investor · Portland, OR · Member since 2013 · 143 posts · 105 votes
11y
Too many variables to really say, ceiling height, square footage, layout, etc will all affect it. Some basements have really low ceilings a feel like a dungeon with no natural light. Some attics will have weird layout issues and have to be big enough to make something usable even with the sloping ceilings. It’s totally dependent on the individual building. I will say you can usually get more usable square footage out of basements simply because you’re dealing with walls and not sloping roof lines. Taxes are totally based on assayed value so if you increase the value of the property taxes will go up. How much is based on how much the value goes up and what your area charges for property taxes.
Investor · Atlanta, GA · Member since 2013 · 3k+ posts · 3k+ votes
11y
Appraisers aren't allowed to count sqf of rooms that are mostly below ground, so, on first glance it would be worth more to finish the attic, if it can be done nicely.
Rental Property Investor · Mercer Island, WA · Member since 2008 · 22k+ posts · 14k+ votes
11y
Basement footage is worth very little and finished vs. unfinished makes little difference.
Building codes mandate minimum ceiling height, access and egress requirements that make make it difficult to add much footage in an attic. Plus you may have structural issues. Framing members that are adequate for ceiling joists may not suffice for floor joists. So you may have to spend more money to get less footage. Upper floor footage isn't worth as much as ground floor, but its worth quite a bit more than basement footage.
The basement would be a great option because of the ability to rent now or at a later time. You will be able to offer private entrance without disturbing your primary residence. The attic would depend on the structural integrity of the roof members supporting the build-out. Not sure about the taxes though, however, your city's building officials should be able to provide some answers or lead you in the right direction.