We have an addition on our house built on a slab. My question is that I would like to raise the floor app. 6 inches (it is currently a step down) . This would make it level w/ the ajoining room. Head height / clearance is not an issue. I would like to put in place a new wood floor system (joists) on top of the concrete. What issues will I need to address w/ this project? Thanks for any info!
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Piece of cake. Assuming you want the finished wood floor the same height as the existing floor, measure the new wood (probably 3/4" if ytou are using solid flooring), add 3/4" for underlayment plywood = 1-1/2". Subtract that from the height difference of the slab and the existing floor (6 in) = 4-1/2" sleepers or joists needed. Does the new slab slope? Then you need to rip the sleepers in a matching taper so the tops end up level. Lay out the sleepers on 16" centers, add blocking to keep them vertical and square, glue and screw the ply on top of them, and thenm add the floor. That's it in a nut shell. There are several other details that need to be adressed, but this will get you thinking.
I'm sorry, I thought you wanted it done the right way.
Thanks for the info! One question I had was in regards to insulation / moisture barrier beneath the floor system (on top of slab) . What's required?
I can't give you a good answewr there, cuz I'm not sure I know. Hopefully there is a vapor barrier under tyhe slab. How old is the slab? It will give off moisture for a few months.
I'm sorry, I thought you wanted it done the right way.
Interesting that you should ask. I just attended a building science conference where there was some disagreement about this issue. Your case is a little more complicated. First off, what is your climate? What is the flooring and even more important, what is the floor finish? Is there a vapor barrier under the slab?
Please answer these three questions and then I will attempt an answer to your question. Be wary of an answer you get in absence of this info.
Edited 8/5/2005 7:04 pm ET by RayMoore
Ok- I live in Indiana ... you can guess the climate. The addition in question was built in 1975 ( main house 1971 ) . Moisture barrier under the slab? I can only guess. the floor covering was carpet, which has been removed. Questions / comments?
A new slab will give off moisture for severaql months ... obviously you are past that point. The next step would be to check for excess moisture. Tape a piece of plastic to the slab, about 2 ft square, tape all the edges tightly. In a day or so look to see if any moisture has condensed on the underside of the plastic. If not, you are probab ly ok.
I'm sorry, I thought you wanted it done the right way.
Follow Ed's directions and add this. Use sill seal or equivelant to form a capillary break between the concrete and the wood. Use 1.5 inches of Expanded Polystyrene foam insulation cut snug between the wood members. This will reduce your heat loss in the winter and keep your floor warmer. Consider backsealing the wood to reduce seasonal movement. If you have a security system, check into adding a moisture sensor to the system in case you have a water leak under this floor.
These suggestions are listed in the order of importance. You may ignore the last ones but not the first few.
This is all good info...thanks Guys! I'll file this all away until I begin this project. Also, would it be necessary to anchor a few of the joists to the cocreate to eliminate any "bounce" of the floor? The size of the room is app. 24 x 34 feet. Thanks again, Tom
Are you saying that you would not lay PT sleepers directly on an interior slab?
I've done this a couple times. I prefer to not have the "joists" in contact with the crete, and the crete surface is more than likely not perfectly straight, creating extra work to fit to it.So I use a smaller size joist and allow air space under it, then shim as often as needed to shorten spans and eliminate bounce. I place those shims with PL Premium.If Indiana has a moderate climate, I would probably only insulate with foam at the perimeter
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I live in North Indiana. 60 miles from Chicago. summer 100 degrees, winter -10 degrees. Indiana/Kentucky border would be much different. No profile so can't tell where he is from. I do it like you said. Shim the joists up, use the glue, and foam between all.
You could do it either way ... pt sleepers scribed to the slab, or shims like Piffin says. Either way i would use some good size blobs of PL to keep the sleepers in contact wioth the slab, although a floor the size he is talking will be heavy enough that it should not go anywhere.
I'm sorry, I thought you wanted it done the right way.
I would rough-scribe the sleepers to the slab (actually, I'd do a laser-level take off to get the slope on each line, and then rip those slopes into the 2x's), and shim with scrap asphalt shingers to compensate for dips and blips in the concrete. Lay a nice thick bead of PL Premium full length under every sleeper, and screw the sleepers down hard to the slab with TapCons.
Then stringline the tops of the sleepers and top-shim any remaining low spot or plane off any high spots.
Then scruNglu the subfloor and go to town on the hardwood....
If he doesn't do this, he's gonna have squeaks, bounces, and yadda yadda forever in that floor system, no matter how big it is.
Now, personally, I kinda like floors that squeak here and there. Adds character. But people I know who talk to normal humans from time to time tell me they hear squeaky floors are a big call-back generator....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
You must use some really long tapcons to go through the sleeper and get enough bite into the slab.
I'm sorry, I thought you wanted it done the right way.
Nope, not that long. I just counterbore the sleepers before I start laying them down.
We usually clamp a 8 or 10 at a time in a couple of Workmates and gang drill them. We'll use a 5/16" spade bit or power auger with a depth-gauge of some sort and bore down till there's about ¾-1" of meat left. Then we set the sleepers on the mark and drill right through into the concrete using a Bulldog. Put a 6" long Robertson bit in the gyprock gun and use 1¾" Tapcons. Works like a charm.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
I don't mind floors with character, "squeaks" either.
Just watch it trying to sell that to some 20-something couple. They want a Victorian. All the gingerbread and wallpaper etc. has to be absolutely authentic. But the floors gotta be solid and flat as a concrete slab and the siding's gotta be Canexwel fibre-cement. For these type of youngsters, 'Character' is only skin deep....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.