Replies

1. 
   mbbailey123 | Oct 16, 2002 10:50am | #1

   Ron,

   That is a problem. There are several materials that you can cover the slab with to prevent moisture from seeping through. Any good structural engineer can give you a list of materials. They would probably charge you a 1 hour consulting fee. I would use a spray-on insulating material in addition to the moisture barier to minimize the temperature difference between the room and concrete. That should keep condensation from forming on the inside. You will also need to use PT trated wood to support the floor.

   Good luck,

   Mike

1. 
   burbankron | Oct 17, 2002 06:11am | #6

   Thanks for your input.  I'm going to look into that.

1. 
   mbbailey123 | Oct 18, 2002 01:52am | #9

   Ron,

   There is something else you may want to consider. Fill all the space under the floor with foam insulation right up to the tops of the floor joists.  Then put a moisture barrier over everything. That wont leave any room for moisture or air to form mold or mildew. It will cost a little more, but be a far easier process to complete. It will also result in a much more comfortable room.

   Mike

1. 
   burbankron | Oct 18, 2002 05:57am | #12

   I was thinking along that line, of insulating the void completely.   Is that a spray type foam insulation, or foam board?  If spray type where can I find it?  Thanks for the help. 

2. 
   1110d | Oct 16, 2002 05:34pm | #2

   I caught a sniff of a problem in your post. You suggested that the slab was not stable, yet you used it to support your new floor. If the slab was indeed settling, then it will proably continue to settle and will cause your floor to also settle in a simular manner. This, as Martha would say, "is not a good thing." I also want to verify that the sill plates which are in contact with the concrete are pressure treated.

   Anyways, I guess the most feasible method that I can think of would be to put down some 6mil poly below the sill plates. The problem is that you have already have the floor built, so there will be too many seams in the poly for it to seal. If you can slowly feed it below the joists, I would try to explore that option. It will be a pita, but it's the best way. I guess the next best choice would be to place it above the joists, below the sheathing. The problem is that you will be trapping the moisture in the cavity where it can cause mold and rot. Depending on the moisture and ventillation levels this could occur any where from months to decades. Ultimatly, I'm thinking that if the floor is already built, that you may be sol.

   There may be another problem with the insulation. Depending on your climate, the vapor barrier should go on the warm side of the wall. If you are in a southern climate, then the vapor barrier should go on the concrete side and there is no problem. If you are in a heating climate (which I suspect) then the vapor barrier should go below the sheathing. But this will create that moisture trap like I had mentioned above. I'm thinking that if you are in a heating climate, that you may be better served by not insulating the floor. The floor shouldn't be too cold because the ground/slab will have a tempering effect.

   
   

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   Edited 10/16/2002 10:43:38 AM ET by Tim

1. 
   rjw | Oct 16, 2002 08:57pm | #3

   Tim,

   I'm curious as to why you said: "If the slab was indeed settling, then it will proably continue to settle"

   I don't have any particular knowledge or a strong view either way, and am just wondering what you're thinking of.  My general impression is that after 5 - 10 years, depending on soil type, settlement of disturbed soil will cease.

1. 
   1110d | Oct 16, 2002 10:43pm | #4

   Ummmm...it depends. One would naturally assume that you would be correct. However, we can not professionally make that assumption as the risk is unacceptable. The home owner wouldn't be very happy with us if we had to tear the entire floor out of a room and repour the slab. A few cracks that are still in the same plane wouldn't bother me, but when there is enough settlement to require over framing, I'd be concerned.

1. 
   rjw | Oct 16, 2002 11:23pm | #5

   Tim,

   Good points,

   Thx

2. 
   burbankron | Oct 17, 2002 06:33am | #7

   Thanks for considering my problem.  Answers to several of your concerns. 

   The house is 25 years old, I'm hopeful most of the settling is done, however, we supported the floor off of 4x4 pt posts (we busted out the concrete in various spots, dug down about 2 feet, and cemented them in) much like a deck. 

   I also have 2-3 inches clearance between concrete and floor joists minimum, more where the floor sunk, so I should be able to put down a vapor barrier without too much trouble.

   I live in cold weather climate, Ohio, so heat loss is an issue.  I have considered not insulating the floor joists, but won't the heat from the room in the winter meeting the cooler air from the ground cause condensation in space below?  Please advise.

   Thanks for your time, Tim.

1. 
   1110d | Oct 17, 2002 04:48pm | #8

   Yes, the moisture (not heat) will want to condense on the concrete slab. That's where the moisture barrier will come in. No matter what happens, it needs to be on the warm side of the assembly. If you choose to insulate the floor, the moisture barrier needs to be below the sheathing. If you don't insulate the floor it can go below the joists. Obviously there is less chance for rot if the moisture barrier is below the joists.

1. 
   burbankron | Oct 18, 2002 05:53am | #11

   Thanks for clarifying.  These are good points.

2. 
   JohnSprung | Oct 18, 2002 01:58am | #10

   > supported the floor off of 4x4 pt posts (we busted out the concrete in various spots, dug down about 2 feet, and cemented them in) much like a deck. 

   > I also have 2-3 inches clearance between concrete and floor joists minimum

   You have a couple code violations there.  First, you need a minimum of 18" between the bottom of the joists and the surface below.  That gives you room for your poured in place piers to extend a minimum of 6" or 8" (depending on which code applies in your locale) above grade.  Then you need a PT block to separate your 4x4 post from the concrete. (Maybe those poured in place Simpson thingies would be OK, I don't know.)  If ground moisture is a problem, it'll soak right thru that concrete and into your 4x4's.  The 18" rule also gives you half a chance to get back in there and fix things.  Personally I like a little more so I can crawl on hands and knees rather than dragging myself thru the dirt.

   Another thing required for a crawl space (same for an attic) is ventilation.  You have to have one square foot of opening to the outside world (screened with 1/4" hardware cloth) for every 150 square feet of crawl space. 

   And that's not everything.  Look at Taunton's web site for their Code Check books -- well worth having before you do anything more.

   As for how long it takes for settling to stop, it's real hard to say.  If they covered over a big tree stump or something, it could take a lot longer than 10 years.  I found a soft spot under the North side of my garage, and a photo from 1919 that shows that there were a few trees there before the buildings went up in 1926.

   -- J.S.

1. 
   burbankron | Oct 18, 2002 06:00am | #13

   Thanks for the info.  I'll check out the site.