Floor joists on top of cement (closing in a carport)

[Steve Thomas]

Greetings:

We are planning to enclose our carport to extend our living room. This is going to be an extensive job, as I suspect the existing wall between the living room is loadbearing, but anyway, here's the issue.

Right now when you step out of the kitchen door onto the carport, you step down about 7 inches to the cement, and the cement slopes gently for water runoff. I want to build the floor up to be level with the living room and kitchen floor, make a short hallway to the kitchen door and take out the existing wall. Not only will this provide us a level floor, but it gives me room for HVAC ductwork into the new expansion and to the currently non-controlled climate laundry room. By the way, I won't suffer height problems in the laundry room or the new living room because the ceiling is about 10 feet up now in these two areas.

Obviously, I will have to custom rip the joists so they are level when placed on top of the sloped cement. My question is, do I need any special treatment or protective surface between the cement and the floor joists? I know the cement will sweat some, and I don't want termites and wood rot to ruin my joists. Do I need to protect them somehow?

See the ACSII art below for the planned expansion.

------------------------------------------------- | | | | | | | Existing Laundry Room | | Build up this floor too | | | | |

----------------Doorway-------------------------- | | D D o o o New Hallway o r r w w a a y y | |

----------------Doorway-------------------------- |Fireplace R |(Corner e |Unit) m | o | v | e | | l | o | a | New Living room annex d | b | e | a | r | i | n | g | | w | a | l | l

-------------------------------------------------

Thanks,

Steve

[SQLit]

Any wood in contact with a concrete slab around here must be treated. Unless you on the second floor. Better check with the local regs before you jump into a puddle.

[PrecisionMachinisT]

I think that rather than trying to rip the individual joists I would try and band around the perimeter, hanging the floor joists with metal hangers, and then use 1x4 or 2x4 pressure treated sleepers against the concrete--shim up to the individual joists with cedar door shims.......this gives you a much better chance of getting things perfectly level while also allowing for some air circulation and even perhaps a vent or two......

IIRC, you can span 8 ft with 2x6 joists set on 16in centers ( or was it 12in centers ) so long as theres a support under them every 8 feet.

[Greg O]

What you are descibing would not fly here! Tear out the old carport, concrete and all. New footings, foundation wall, then build the floor system and walls from there. The carprt most likely is just a floating slab with no footings, it will not be stong enough to support the loads of the floor, walls and roof. Done your way, in years the addition will move around relative to the house, causing stuctural problems. Done properly you will be able to match the existing floor heights, adaquate room for heating and electrical, and keep the local building inspector from having a heat attack! Greg

[Dan]

Wouldn't fly in my jurisdictions either, unless you can prove you have a proper footing under the carport. Never saw one that did!

Dan

[Steve Thomas]

Hmm. Hadn't considered that aspect. What do you mean by floating slab?

It's hard to guess about the original construction, because the house had an addition put on the opposite end of the structure in the 70s and a total brick veneer was added at that time.

I suspect, however, that the carport was original construction and I think it is an integral part of the house. The attic extends out over the carport (in fact, that's where the attic access is) and the laundry room is on top of the same slab. The carport slab was poured right up against the wall of the house. How can I explain this? I'll attempt with ASCII art again.

-------------- |XX| | |XX| | |XX| |

--------------

Where the X's are is the carport. The outside wall cinder blocks (which can now only be seen from inside the crawlspace because of the brick veneer) seem to continue out to the carport, not "turning the corner" at the edge of the crawlspace.

I suspect that the entire structure was laid out with the cinder blocks from the edge of the carport on the left side to the (then) outermost wall on the right side. If that is so, then the carport slab doesn't "float", right?

Using the little drawing above, the left edge of the carport is nearly

18" above ground level. The driveway was built up to the front of the carport so it would reach.

Would that still constitute a "floating slab"?

I'd be willing to temporarily remove some of the bricks from the little 18" wall to prove the cinder block construction of the carport. If I'm right, the cinder blocks would support the walls, correct?

[Greg O]

Hard to say what you have! A floating slab is a slab for a garage or driveway that has no fooltings or foundation, generally just has a thickened edge. The center of the slab may be only four inches, but around the edges it my be around a foot thick to reinforce the edge. Garages and driveways are often biult this way. The big question is if you have a foundation wall to support the side of the carport that is away from the house. If you simply dig down along the slb you should be able to find out. A footing and foundation will most likely extend 3-4 feet down, depending on the frost depth in your area, and building practices. I think you need to get a local building inspector or a engineer to help you make these desisions! Greg

[raven]

Gotta go with Greg here. What may be a resonable solution is to hammer through the car port slab in a few places and place piers down below the frost-line. Your addition would be built on those piers and actually be suspended above the car port slab (which would be left in place).

John