subfloor on slab opinions


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Old 09-21-05, 05:27 PM
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subfloor on slab opinions

I'm looking to finish off what is currently a screened in room that is on a concrete slab connected to the back of the house. The slab is above grade and the final flooring will be engineered hard wood. My question is what to do for a subfloor. Some options I've come up with are:

1. 1/2" plywood on some 1x2s on a moisture barrier with hard insulation to fill in
2. forget the 1x2s, put the hard insulation down, and 1/2" right on top of it. Kind of floating on the polysterene. Will this (or something else) be dense enough to not crush without the wood framing?
3. Dricore, with eng. hardwood directly on top of it. I really like this solution, but will the ~R2.5 of Dricore be good enough on an above grade slab? I live in Western Mass so it gets pretty cold in the winter.
4. Delta-FL and plywood? I don't know much about Delta-FL, but it seems it's cheaper than the dricore will be.
5. Finally, Delta-FL, hard insulation on top, then plywood.

I really don't want a cold floor, however height from slab to ceiling as is is regular height, so I want to have as shallow a subfloor as possible.

Any advice greatly appreciated,

Thanks
 
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Old 09-21-05, 06:01 PM
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When you say "finish off" the screened in room.... does this entail heating/AC (climate control).

I ask because I'm installing an engineered wood floor at the moment - glueing it right down on the concrete slab. But the space is temperature/humidity controlled. Looks great, feels great!
 
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Old 09-21-05, 06:51 PM
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Originally Posted by thezster
When you say "finish off" the screened in room.... does this entail heating/AC (climate control).

I ask because I'm installing an engineered wood floor at the moment - glueing it right down on the concrete slab. But the space is temperature/humidity controlled. Looks great, feels great!
Yah, forced air AC/heating. My ducting question is in the other forum. I would think right on the concrete in New England would freeze my feet off and cost a fortune in heating. Which is why I wonder if the dricore is a good enough R value for my application.
 
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Old 09-22-05, 01:29 PM
Yak
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I'm doing a project very similar to yours, although I think my old subfloor tapers. I was thinking about attacking mine like your option #2. Being a novice at subfloors, I thought I would check out what the opinions are. I know that the type 250 polysterene is for extra load, but I think Menards and others only carry it in 2" (probably special order). It would give a better R value at 5 (some are 6.5), so I thought of this option. I did use tapered board on my flat roof, so I may look at doing that, depending on the slope. Option #5 looks good too, probably the best in my opinion. The Chicago winters are bad too, and the room is unheated, BURRRRR.
 
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Old 09-23-05, 08:32 PM
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Subfloor

My vote is for Dri Core. Use it alot where it gets really cold. Like 50 below for several days. Not one complaint. If there is a heating duct on the floor, I take part of the duct on one end and just cut a hole and let it go under the Dri Core floor. At the other end of the room, I leave a small opening for air to travel. Now you have a heated floor. Dri Core in engineered to put hardwood or any other glooring right over it. It is a little more expensive, but in my opinion well worth it. Good Luck
 
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Old 09-24-05, 04:35 PM
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Originally Posted by Jack the Contractor
My vote is for Dri Core. Use it alot where it gets really cold. Like 50 below for several days. Not one complaint. If there is a heating duct on the floor, I take part of the duct on one end and just cut a hole and let it go under the Dri Core floor. At the other end of the room, I leave a small opening for air to travel. Now you have a heated floor. Dri Core in engineered to put hardwood or any other glooring right over it. It is a little more expensive, but in my opinion well worth it. Good Luck
So you're pumping warm air between under the dricore between the concrete and subfloor? Now maybe I'm showing that I never took thermo dynamics or something that really talked about heat transfer for more than a chapter (not too mention what I did take was many years ago and never applied), but this sounds like it would waste time in heating a whole bunch of concrete and very little floor. To my untrained eye, this just doesn't sound logical. If the idea of the dricore is to insulate from the cold, wouldn't it do the same with the heat you are pumping in?
 
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Old 09-24-05, 05:17 PM
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Subfloor

No it does not. Between the dri core and the concrete are rubber feet. The space is only 1/2". All we do is make it so there is a little air flow, between the subfloor and concrete instead of being all sealed up. This keeps the concrete dry and warm. Cold concrete breeds mold and mildew. This keeps it warm and air flowing, and also adds warmth to the floor. There is no pumping as you suggest. If you lay foam on your floor, you seal the concrete and mold and mildew will happen. It is a fact. If you put down 1 x 4 slats, with plywood over it now you have an air space to keep the concrete dry and airy. We do the same for 1 x 4's and plywood. We set up an air flow if possible with a air return. That is just good construction. Dri Core just makes it a whole lot easier and less expensive. The idea of Dri Core is to also keep your floor up off of the damp concrete as well as insulate. I was telling you what we do when we are asked to install a sub floor, which is alot of the time. You can do yours however you like. I was just answering your questions. Good Luck
 
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Old 09-24-05, 05:55 PM
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Originally Posted by Jack the Contractor
No it does not. Between the dri core and the concrete are rubber feet. The space is only 1/2". All we do is make it so there is a little air flow, between the subfloor and concrete instead of being all sealed up. This keeps the concrete dry and warm. Cold concrete breeds mold and mildew. This keeps it warm and air flowing, and also adds warmth to the floor. There is no pumping as you suggest. If you lay foam on your floor, you seal the concrete and mold and mildew will happen. It is a fact. If you put down 1 x 4 slats, with plywood over it now you have an air space to keep the concrete dry and airy. We do the same for 1 x 4's and plywood. We set up an air flow if possible with a air return. That is just good construction. Dri Core just makes it a whole lot easier and less expensive. The idea of Dri Core is to also keep your floor up off of the damp concrete as well as insulate. I was telling you what we do when we are asked to install a sub floor, which is alot of the time. You can do yours however you like. I was just answering your questions. Good Luck
I didn't mean to sound like I was doubting you, was just trying to understand. To a layman, what you said just was something that I never would have thought of. If I understand, would the same effect be had by tying a small feed into the return, and then simply have a small opening on gthe other side? The air being drawn through the floor would be room temp, rather than heated, but it sounds like the flow is more important that the temp as long as it's warming than what it wants to be.

Or can I have a full return under the floor? The problem I have right now witht he slab is how to easily get new heat into the room. I'd prefer to have the heat duct go to the outside, but that would mean going up the inside wall, through the attic, and then down. Could I use this technique to simply send the warm into the room from the inside wall, then have the return air drawn to the register near the outside wall and returned under the floor? If this would work it would be awesome. Or should I go about ducting another way?
 
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Old 09-24-05, 07:02 PM
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Subfloor

From what you described if I understand you correctly, it should work just fine. All you really need is an opening for air to get in, and air to get out. Anything else is just gravy. I was not using the heating duct for heat, just for air flow and a register pushes air so it was like having a little fan. Good Luck
 
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Old 09-24-05, 07:14 PM
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Originally Posted by Jack the Contractor
From what you described if I understand you correctly, it should work just fine. All you really need is an opening for air to get in, and air to get out. Anything else is just gravy. I was not using the heating duct for heat, just for air flow and a register pushes air so it was like having a little fan. Good Luck
Awesome, your stock in dricore will soon go up, enjoy the extra dividends. Giving me an adequate way to move some of the heating around without having to do a decent amount of duct work has pushed me over the edge.

Thanks for your assistance.
 
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Old 09-24-05, 07:18 PM
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Your welcome.
 
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Old 09-26-05, 01:09 PM
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Sorry, don't mean to beat an apparently dead horse, but as I stated above; my situation is similar to the one stated. The Delta FL is similar to the plastic base on the Dricore. His option #5 used hard polystyrene insulation between the plastis Delta FL and the plywood. Given it's R value of 5/in, wouldn't this option make sense? My subfloor tapers, so I think I could use about 1 to 2", giving a R value of 10. Also, you don't state a vapor barrier. It doesn't need it because of the airflow, correct? would you do two layers of plywood? I thought I remember reading to overlap two layers, or is this overkill.
 
 

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