# Building a SubFloor on a concrete basement



## dberladyn (Apr 24, 2011)

Hi, 

Well I figure I should share my plans with someone who might know what they are doing more so than I. I am tired of having a cold basement, I should have dealt with this the first time round. I'm renovating... this is my second time.

Anyways I want a subfloor. We've had carpet on concrete and tile on concrete and both have been very uncomfortable. I am completely gutting our basement, everything is getting stripped down to what was here when the house was built. (nothing!)

My plans are to lay either 1/2, 3/4, or 1" Expanded Polystrene (pink or blue styrofoam) and then glue either 5/8" or 3/4" Tongue and Groove plywood to that. The thickness of this floor will be determined once I install a new exterior basement door. That's the only reason I haven't chosen a thickness. My thinking is that the thermal break from the concrete is far more important than the actual R value. I even considered Cork instead of the styrofoam.

Does anyone have any input? I know I can screw the subfloor to the concrete but I honestly like the idea of a floating floor better. If I build walls ontop of this subfloor they should hold it down right? I just think for future renovations, water leaks, etc. It would be much simpler to take a skill saw and cut through the plywood and not have to deal with screws. Not only that, then I have no worry of damaging the concrete underneath.

Would I be wrong to lay styrofoam down no glue or screws and then bond a plywood floor to the styrofoam? Do you see issues? Any advice?

Thanks.


----------



## Bud Cline (Mar 12, 2006)

Did you mention what you will use for a finished floor covering?

Before you throw all that money in the dumpster why don't you consider heating the floor?


----------



## dberladyn (Apr 24, 2011)

Flooring will be either carpet, commercial grade vinyl tile, or linoleum depending on the room.

As for heating the floor.... Our electrical panel is maxed out. I'd either need a a subpanel installed or possibly even have the whole service upgraded. I haven't looked into that because I haven't wanted to do it.

I honestly think it'll be fine downstairs as long as I can get a thermal break between the concrete and the finished floor.


----------



## ridge-runner (Dec 27, 2011)

dberladyn said:


> Hi,
> 
> Well I figure I should share my plans with someone who might know what they are doing more so than I. I am tired of having a cold basement, I should have dealt with this the first time round. I'm renovating... this is my second time.
> 
> ...



Iv done 3 jobs similar. However. 
1.i used 2" sm foam (blue 2x8 t&g foam) adhered with pl premiem.
2.then layed residential vapour wrap. Adhered with pl premiem
3.i used 3/8" t&g ply (tap con/bluescrewed/concrete screws)to floor.+ pl premiem
Then framed over that.

Thats how iv done it. Some may say overkill but like they say better to much then to little!!!

Also. Ur plan for if leaks occur. Very good idea. The houses i was doing where all new foundations within the last 4 years and no sign before so i when permanent your call but youll have better efficency if you adhere and screw


----------



## joecaption (Nov 30, 2011)

In my own slab house I used 3/4 blue foam board then 3/4 Advantec T & G Tap Coned through to the slab. No glue used at all. 
Solid as a rock, no longer cold and it did not raise the floor above my ext. doors threshold.
I used Allour strip vinyl flooring and I can step down hard right near the baseboard and not see the floor move down at all.


----------



## monicawats (Dec 27, 2011)

The flooring system should prevent moisture from condensing onto the concrete surface because it blocks cold conduction through the concrete floor slab. To begin the process of installing a basement subfloor, you should first confirm that you do not have a water problem in your basement.


----------



## rusty baker (Feb 13, 2009)

The foam board will eventually collapse. It is not made to walk on.


----------



## dberladyn (Apr 24, 2011)

> The foam board will eventually collapse. It is not made to walk on.


I think the same at times, but then isn't that why people use the blue or pink styrofoam? For strength/density? Is there a density difference among sheets? I have a feeling it's a risk, but not much of a concern unless you were placing extremely heavy furniture/equipment on the floor. I also think the thinner the styrofoam the less chance of it compacting over time.

By the way, I did see a dricore type system in Home Depot. 3/4" foam with chipboard on top, 2x2 tiles. Not that Home Depot wouldn't carry an inferior product but... I think the system works for typical human living space. Do you have any alternatives to suggest?



> The flooring system should prevent moisture from condensing onto the concrete surface because it blocks cold conduction through the concrete floor slab. To begin the process of installing a basement subfloor, you should first confirm that you do not have a water problem in your basement.


I know... use poly and seal it to the concrete to test for moisture. Call me crazy but I don't think it's a concern in this house. Even if it is, the styrofoam will act as a moisture barrier anyways, will it not?



> In my own slab house I used 3/4 blue foam board then 3/4 Advantec T & G Tap Coned through to the slab. No glue used at all. Solid as a rock, no longer cold and it did not raise the floor above my ext. doors threshold.
> I used Allour strip vinyl flooring and I can step down hard right near the baseboard and not see the floor move down at all.


Everyone likes to screw to the floor... maybe I should just give in and do it... but why doesn't anyone have an opinion on letting it float freely? When you screwed it down do you remember if the screws sucked the floor down? I guess I'll have to wait and see when I do it.


----------



## rusty baker (Feb 13, 2009)

Good luck, you will need it.


----------



## Bud Cline (Mar 12, 2006)

:scooter:


----------



## Gary in WA (Mar 11, 2009)

http://www.buildingscience.com/documents/insights/bsi-003-concrete-floor-problems?full_view=1

http://www.buildingscience.com/documents/reports/rr-0309-renovating-your-basment

http://www.cosella-dorken.com/bvf-ca-en/products/foundation_residential/floor/products/fl.php

Gary


----------



## dberladyn (Apr 24, 2011)

GBR in WA said:


> http://www.buildingscience.com/documents/insights/bsi-003-concrete-floor-problems?full_view=1
> 
> http://www.buildingscience.com/documents/reports/rr-0309-renovating-your-basment
> 
> ...



EXCELLENT links Thank You! Perhaps some others should read these as well.


----------



## Terabitdan (Dec 29, 2011)

*Delta-FL*

I'm just finishing up completely renovating our basement after a flood this spring. In our case we had storm water backup from the drains, not from the walls. After reading the building science website I went with Delta-FL on the floors with a similar product on the walls, moisture proof tape all the seams, back-flow preventers in the drains. We then laid 3/4" T&G plywood tapcon into the cement. It's rock solid and a huge temperature difference in the basement. The walls have 1" XPS inside the membrane. We are just finishing up the drywall and the flooring is next. 

I'd highly recommend using Delta-FL or a similar product rather than insulation under the plywood. 

Dan


----------



## dberladyn (Apr 24, 2011)

Hi Dan, 

Thanks for your post. I have to admit I didn't do a lot of research, not near as much as I usually do when I build something but I'm content with my decision. I went with Delta-MS topped with 3/4 T&G Plywood. Where ever there's a really heavy object like a fridge or freezer I'm cutting a square in the Delta-MS and laying down 1/4" plywood strips that have been completely sealed with Canadian Technical Tape (US Version?).

It's a fairly simply system to install. I did come up with the idea of 2" strips of 1/2" treated plywood, poly then the plywood... it would have been stronger on 12" center's but this will do quite fine for living on and it's fast.

Thanks again for the post, you swayed me. I'm glad I didn't go with the styrofoam. The air gap makes more sense... if it wasn't for that, a guy could lay 2" strips of 1/2" treated plywood with 1/2" Styrofoam in between, taped and sealed shut.

There's probably a million ways to build a subfloor.

Dan


----------



## epson (Jul 28, 2010)

GBR in WA said:


> http://www.buildingscience.com/documents/insights/bsi-003-concrete-floor-problems?full_view=1
> 
> http://www.buildingscience.com/documents/reports/rr-0309-renovating-your-basment
> 
> ...


Yes those are excellent links…:thumbsup:


----------

