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enclosing carport.....remove cement slab??

15 years ago

In the future I plan on enclosing my carport to make another room. Our house has a crawlspace all the way up to the wall where the carport is. I have heard different stories on the best way to go about this, and want to get some more advice.

Obviously, it would be easier to just run my floor joist above the cement slab and leave the slab there. But, I live in SC and we see a wide range of weather, very hot and muggy to cold and wet days. The cement sweats a good bit.

There are no mold issues underneath the crawlspace, I open the vents in the summer and ventilation is fine, house is in great shape for being almost 50 yrs old. My concern is that if I build over the slab, I am asking for a mold problem.

I have heard of the vapor barrier, but not too familiar. At one point I had put some plastic down underneath the house to do some plumbing work, and this trapped the moisture between the dirt and the plastic sheeting and mold began to grow underneath the plastic. I took the plastic out, and now everything under the house is dry and just fine. So, if I put a moisture barrier over the slab, isn't that just going to let mold grow under the plastic?

I would appreciate any advice on what to do here. I don't plan on starting this project for a while, but I wanna know what I'm getting into here!

thanks,

Paul

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Comments (5)

oruboris
15 years ago
When you say 'run the floor joists above the cement slab', you do mean 'above' and not 'on', right?

If so, I don't see where it would make a difference.

But I really have no experience with your part of the world. Is the slab 'sweat' a funciton of high humidity condensing on the cooler slab, or is it moisture from below the slab soaking upwards? The answer to that might influence the answer to your initial question...
davidandkasie
15 years ago
the moisture barrier goes on the bottom of the floor joists. build them up enough to allow air flow and you won't have any issues with it.

in my area slab sweating is usually due to high RH.
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paulflyboy
Original Author
15 years ago
yes, the floor joist will be about 1-2 feet above the cement slab. the humidity causes the slab to sweat, it doesn't do it everyday.

ok, that sounds better with the moisture barrier. never would have thought of that.

thanks for the replies!

paul
susie53_gw
15 years ago
When we bought our house there was a room between the garage and the kitchen that had been enclosed. It had been an open breezeway before. They put 2 X 4's with insulation in between them down and then a plywood floor with carpet on top. Well, in time it drew moisture and what a mess. We ripped it all out and di it the right way. The funny thing was a step that came up into the kitchen was cement. We left it and it has worked for 40 plus years now... Susie
kitchenredo2
15 years ago
The first thing would be to research the building codes for your jurisdiction. This will dictate what you can and cannot do with regard to this project, including applying for the appropriate building permits.

I am adding an addition where I currently have a carport (my existing roof extends over this space). In my case, we will have to dig down under the existing slab to determine how the existing roof is being supported. What we find, along with the building codes, could change the scope of the project. And just because it exists, does not mean the previous owner did the construction correctly or current code will apply.

Good luck and expect the unexpected....

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