Expert: Dan Griffin - 10/30/2010

Question
Hello, I hope your available to answer my questions..I am a woman not familiar with construction terms so I hope I can properly describe my situation well enough for you to formulate an answer. Ha ha
We purchased a home in May of this year that was originally built by a "commercial" concrete guy. (The house is stick built but I use it for reference later)The home was built in the early 1960s. At some point, he excavated into the lot like you would for a "drive under" type garage...except there is no part of the home that actually sits above this garage.
He added a two car garage/butted up to the original full basement foundation or outer wall, which faces West. Home is orientated North and South almost on top of an elevated  1/2 acre lot-it is not "flat" to street(front north, back south) He then stuck a driveway access to the two car garage from the street (which is LONG) about 35-40' on each side are sloping cement retaining walls (High end near garage slowly decreasing in height towards street) I have no idea if the info is helpful or not to my question but I'm trying to give as much info on "geography" as I can.
The garage itself is cement...two cement walls built off of the original basement, exterior center support (also cement) in the middle of the two garage doors. The "ceiling" of the garage is made up of all cement "t" s. (is that the right term?) Its like flat cement looking up with cement "beams" I'm told those are called "T" s. The T's are orientated one "end" North, other South. There is currently nothing but a large (approx: 24'x24' square) cement "pad" above this 2 car garage. It just sits there...the third owner of the house have put paint, other type of inappropriate coverings on top of that pad over the years I assume, to help keep water out. It needs scraped off down to original cement. They also had put an exterior door in the house itself and I guess used this "pad" as an entrance and mail delivery area for a home business.
There is a flimsy metal rail that keeps people from falling off the edge of this pad down at least 15-20' onto the "driveway".
HERE'S THE QUESTION: We are wanting to build out over that cement pad for additional living space above the garage. We have young children in the house and I worry about one of them slipping out that exterior/old office door and falling despite the rail. We could also use the room...my husband wants to put like a den and storage area out there, utilizing the exterior doorway to enter this new addition. Our problem? No one can tell us if structurally, the T's and garage could handle building out on it. Basically it is a big two car sized cement box...the t's are structurally fine, no evidence of cracking, etc...there is an angled crack down by the garage door area (in outer wall, not wall where doors are) that extends up towards the t's...it does not appear to go all the way through, more of a hairline we intended on repairing professionally, shooting in epoxy. It does not and has not ever leaked or showed signs of moisture near this crack. There has been more of a leak water drip issue in heavy rains up next to the house and down...some of that would be cured by the roof out over the whole thing I assume...but nothing leaches in from the ground and we've had enough heavy rain to know.
So based on my really long winded information? Does this cement "box" sound like something we could build out and over? Only single story...roof would be tied into existing roof, etc. It has been suggested to me that because the two exterior cement "foundation" walls would bear alot of the weight, that perhaps we'd have to form and pour a 2nd cement wall or sump block on the two sides for extra support but that would obviously add considerable expense to the project. Any thoughts? I could send photos later if it would help? THANK YOU FOR ANY GUIDANCE OR ADVICE YOU CAN PROVIDE>>>EVEN A SHOVE IN THE RIGHT DIRECTION WOULD BE HELPFUL! I look forward to hearing from you, Stacey

Answer
Stacey, you will need to find a structural engineer who can see the situation to determine a reasonable course of action.  Concrete twin tees, concrete walls, and the footings to carry them should be more than adequate to  hold a second floor.  As you said, roofing over the joint between house and garage should do away with your leak.

It sounds quite reasonable to be able to use the structure, but again, local code officials will expect an engineer's stamp on your drawings as there are no standard tables to use for what you intend.

I sure hope thios helps get you going.