Expert: Richard Taylor, AIA - 2/9/2008

Question
We are thinking of adding more living space to our home. We have an screened in deck on the back of the house and it is complete with proper roof and supports, can we just remove the deck board and insulate the floor and rebuild the floor and then enclose or do we have to put a foundation in?

Answer
Hi Dorothy - thanks for your question!

Building codes sometimes won't let you do that.  Once you enclose a space, it has to meet all the requirements of a "habitable space" including heating, insulation, electricity, and so forth.  You'll also be required to keep all wood at least 8" above ground, and you'll have to keep a minimum amount of space between the ground and the underside of the floor joists.  If your deck is close to the ground, that might be a problem.

From a practical standpoint, it will be difficult to keep the room properly heated and cooled without a crawlspace or basement underneath.  The insulation you place between the deck joists won't be very effective if it's exposed to the outside or even just covered with plywood.  Plus, you need to allow for ductwork below - most times this means dropping a false ceiling below the floor, if there's room.

From a structural standpoint, as long as the deck's in good condition you should be ok.  But since you're going to invest money in the enclosure, be sure to thoroughly check the existing construction first.

Finally, check with your local building department - they'll tell you what's possible within the limits of your local building regulations.

Hope this helps,

Richard Taylor, AIA
www.rtastudio.com
www.rtaplans.com