# installing a basement subfloor on concrete



## yurij (Dec 29, 2008)

Hi - I have a poured concrete basement with no water issues. I want to install 3/4" hardwood flooring (not the engineered kind) in the basement. My plan is to build a subfloor by laying down 2x's (flat side down) as joists (16" on center), then putting 3/4" OSB sheets on top of this, and then nailing the flooring on top of this. I have looked into dricore but like my solution better. I plan to leave a 1/2" gap by the walls, for expantion and also to let the area underneath vent. My question is
1) I am thinking of putting some vapor barrier between the real floor and the subfloor. but i am not sure if this is usefull in this application. but if i do, what product should i use and where should it go? Seems i have 3 choices:
   a) lay the barrier on te concrete and place the joists over it?
   b) lay the barrier on top of joist and put the OSB over it
   c) lay the barrier on the OSB and put the flooring over it
2) Will tha vapor barrier serve any purpose if there are those expansion areas around the permiter to let the vapor escape into the room?
3) Is real hardwood flooring going to be a problem even on this subfloor?

thx in advice for any advice  -yurij


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## d.n.f. (Dec 29, 2008)

Look at this stuff.

http://www.dricore.com/en/hgtvdisasterdyi.aspx

Hardwood over concrete can cause some real issues.  You have to deal with any potential moisture problems.  I would go with engineered.
Some guys have never had any problems, but for me wood needs to breathe.  By sticking it with plastic on one side is not an ideal situation.

two cents


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## yurij (Dec 29, 2008)

dnf - i have looked at dricore, but i don't see how that solves any humidity issues. the panels fit together with tongue and groove, but do not form a vapor barrier since it requires 1/2" clearance at the walls. the plastic does protect the OSB on the top of the dricore from touching any potentially standing water (1/4" or less) and does provide some thermal insulation.

i am not placing the hardwood flooring on the concrete basement floor. i am literally building a joisted subfloor, except the joists are only 1.5" tall. the joists run the short way in the room (about 24') and there is nothing to block the airflow from one wall to the other aloing the joist "bay" underneath the floor, which should allow any excess water vapor from the floor to emerge out into the room and so equalize the humidity on either side of the wood floor. Having an exceess of humidity on one side of the floor vs the other causes the surface of the flooring to cup. having alot of humdiity everywhere causes the wood to expand and stay expanded as long as the humdiity doesn't change. so i plan to let the hardwood floor aclimate for a while (4 weeks) in the basement, expand to whatever size it will be, then install it. if the humditiy decrease, i get small gaps, between the strips of hardwood, but i will not get a buckled floor.

I don't see what a vapor barrier will do for me.  but thx for the advice. -yurij


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## d.n.f. (Dec 29, 2008)

Well you got the acclimatizing thing right.  Just read an article saying you should install wood flooring at the most humid time of the year.  So if you are installing now you might want to crank up the humidifier.

I think that drycore would just kind of keep the floor a bit warmer.  Your subfloor idea would do the same.  The drycore would be a quicker install but I have never priced it out, maybe it is expensive?

Just watched a Holmes on Homes episode recently where they had to rip up a beautiful wooden floor that was built over a heat slab with a poly barrier.  All kinds of moisture issues.  You would think the heated slab would have dealt with that but not in this case.

Best of luck.


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## yurij (Dec 29, 2008)

dnf - the costing is as follows. 
dricore:  
  1.67 /sqft (home depot)
    .33 /sqft plywood to lay on top of the dricore if you will be nailing the floor.
$2/sqft + labor

subfloor system:
    .35 /sqft for 3/4" OSB
    .20 /sqft for pressure joist system (2x4's ripped in half, evey 16" on center)
$0.55/sqft + labor

it does add up. 
-yurij


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## wingsfan (Dec 30, 2008)

I am pretty sure that they suggest only engineered flooring for any area that is below the surrounding outside grade. I am no exper , but that is what I remmember hearing.


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## Highbeam (Dec 30, 2008)

I am considering a similar project of raising and adding a floor 4" above a concrete slab. A converted garage in my case. I actually desire the concrete floor so I am considering adding vapor barrier, foam insulation, then pouring more concrete level with the top of subfloor in teh rest of the house. It would be simpler to simply build a wooden floor as you describe with vapor barrier, foam, 2x4 sleepers (I wouldn't rip them), and then wooden subfloor. I worry about the wood rotting. 

For sure I would put the vapor barrier against the concrete and even up the sides of the wall sealed with mastic. Note that this makes a nice swimming pool of water should you ever have a burst pipe, leak, or spill above the vapor barrier which will put all of the wood in a nasty situation. 

If I were you I would heat the floor with an electric or hydronic system and then tile it.


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## Dune (Dec 30, 2008)

Are you planning to use pressure treated sleepers?


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## richg (Jan 1, 2009)

You are taking a big risk on this one. If you wanted to minimize the chances of getting moisture intrusion, advice from Mr. Overkill:

1. Drylok the floor and walls
2. 6 mil poly vapor barrier over the Drylok
3. Pressure treated 2x lumber installed with a .22 caliber nail gun
4. Pressure treated 3/4 plywood
5. 30lb roofing felt
6. Hardwood on top. 

That's a lot of effort to go through. If it were me, I'd simply lay down a poly moisture barrier, foam underlayment and put Pergo Select over top. No issues with that setup.


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## LLigetfa (Jan 1, 2009)

Have you done the test with duck taping a square of poly to the floor to see if there is a moisture migration issue?  A floor can look dry as long as it's exposed to the drying air.

DriCore is not a continuous vapour barrier because you don't need a continuous vapour barrier.  The purpose of a continuous vapour barrier is to double as an air barrier which you don't need in a basement floor application.  There is nowhere for air to go down.  All you need is a moisture contact barrier which DriCore will give you.

By code, any wood in contact with concrete must be pressure treated.


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## semipro (Jan 14, 2009)

Whatever way you decide to do it I'd suggest you read this document from Building Science Corp. 
http://www.buildingscience.com/docu...ovating-your-basment/attachment_download/file
Even if you don't follow their recommendations I think you'll find it useful.  

Andy Engel of Find Homebuilding Magazine also wrote a great article on finishing basements.  

Good luck.


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## velvetfoot (Jan 14, 2009)

I've read of laying down an inch of XPS foam, tyvek taping or otherwise sealing the joints for vapor.  Then putting T&G;OSB over that, tapconning into the concrete floor.
I still don't think solid hardwood flooring is for below grade.  Perhaps the engineered wood flooring.
Don't forget, anything you do on the floor will reduce the ceiling height and maybe cause a problem with the last stair tread.


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## Reggie Dunlap (Jan 14, 2009)

I've done it with 2x4 PT sleepers over the concrete. We glue and tapcon the sleepers to the slab. The key to not having moisture issues is to insulate the concrete with foam between the sleepers, and caulk the joints.

It's the temperature difference between the air and the slab that cause condensation, and the insulation should prevent this. This assumes the basement is dry to begin with.


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## billb3 (Jan 14, 2009)

Just pulled an OSB floor out because it was all warped.

Put down ripped 2" sleepers with glue
Sealed the concrete in between.
Put solid foam in between the sleepers for insulation
then  the usual plywood subfloor
then Pergo.

Could have used Hardwood flooring except they raised the minimum ceiling height by code last year and regular hardwood flooring  would have gotten me under by like a quarter of an inch.
No way was I repouring the concrete floor for a quarter of an inch. Shouldn't have pulled a permit.


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## Jack Straw (Jan 14, 2009)

We've finished off quite a few basements and very often the concrete floors aren't level and have high and low spots. You may want to take a 6' level and see how the concrete lays. You made need to do a lot of shimming.


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## theCase (Jan 15, 2009)

yurij said:
			
		

> dnf - the costing is as follows.
> dricore:
> 1.67 /sqft (home depot)
> .33 /sqft plywood to lay on top of the dricore if you will be nailing the floor.
> ...


I agree 100% with your analysis, but having used DriCore it's a great product and I recommend it.  

Reasons:

1) A big advantage of it is it’s size.  I was able to carry an entire subfloor for two rooms at my cottage inside my car (a VW at the time).

2) One person can easily move this stuff around.  No need to call your neighbor when you need to bring it down stairs and wind your way around doors or walk backwards down a stairway.

3) Trimming to fit is a breeze.  hmmm, I need to cut around this door AND this post and take three inches off this side....wheres my wife/son/neighbor to help me steady this on my table saw??? Dang, I measured from the wrong side!  Instead of this scenario, you're trimming a much smaller piece one can easily handle by yourself on a table saw.

4) Speed;  I was able to do an entire room in four hours;  Granted I am not exactly Mr. Handy-Andy, but it went quick!  90% of the time it's just grab a panel and tap it in place with a hammer.

Thats just my 2 cents.  I wrestled with the cost vs. labor issue too, but I have no regrets over the extra money spent.  and if ya watch the sales, you can often get this for less.  AFA what went on top of the sub-floor, I choose carpet tiles purchased from the internet. Lots of the same reasons, but that's going off topic....

Regardless of each persons decisions on such weighty topics, I say "good luck" to all.


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## pelletfan (Jan 15, 2009)

just want to ask the do it your self person of the flooring installation an important question??
We don't even care yet about sub flooring etc. etc.

First: Is this a below grade installation of a solid hardwood floor or an on grade installation.

On grade solid wood floor installation can be done with the correct vapor barriers no issues here.

The story changes completely if it is a below grade. If you have a below grade, I don't recommend a solid wood flooring installation, just engineered.
Solid wood on below grade is just not recommended or from my perspective not wise. You are rolling the dice here! 

Below are some links which are self explanatory:

check moisture, check moisture, check moisture...........

http://www.hardwoodinfo.com/pdf/articles/010609112306Moisture_Testing_-_Concrete.pdf

this one is a good one too

http://www.woodfloorsonline.com/techtalk/woodwater2.html
http://www.woodfloorsonline.com/techtalk/woodwater1.html

I guess I have it all covered. Hope that helps. I have seen just too many failed Wood Floor Installations.


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## Shari (Jan 15, 2009)

Just a FYI:  At our other house one of our young sons was playing in the basement and ended up putting a cardboard box on top of our sump pump.  We didn't notice this until it rained and the sump pump wasn't running.  We removed the box and the pump worked fine - however - because the sump pump could not drain out the water from the perimeter drain tile line, the basement floor was stressed and numerous small cracks appeared.  Then, years later, the pump itself failed and we had water seep up all the small cracks in the floor............  None of this would have been good if there was a sub-floor with hardwood floor on top of it.

Shari


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## Gooserider (Jan 15, 2009)

Don't want to hijack the thread, but I'm also looking at trying to upgrade our basement this year or so...

Our situation is a bit different - the basement floor is about 4-5' below grade, and MOST of the year is above the water table and has no problems.  During spring thaw, and heavy extended rains, we don't get flooding, but only because we have a sump pump that runs often and a lot.  Long as the pump works (and we now have two in a redundant setup) the basement floor stays dry.  However if the pumps die or get turned off, (or we get an extended power failure) then we are likely to get 2-3" of water.

Currently the basement is finished in most rooms, with wood board walls over studs and fiberglass, and some kind of indoor / outdoor carpeting on the floor.  We know it got flooded once as the GF was purchasing the house, and it dried out w/ no problems, however the basement is not really heated enough to be useable living space, I suspect mostly because of heat loss through the floor.  

I'd like to rip out the carpet, and put in some sort of insulating floor, quite possibly with some in-floor hydronic radiant heat, but I want, and the GF insists, that whatever we do be something that could survive a potential flood.  (This has happenned just ONCE in the last 15 years, the PO turned off the sump pump just before she passed papers on the house, which is how we know about the water depth...)  While the current headroom is OK, it's not great, so I also can't do something that would take up a lot of thickness.  I'm fairly open as to what the final finishing material would be, long as it's resistant to potential water damage.

Dricore explicitly says their stuff can't take water.  Owens / Corning seems to say the panels they sell as part of their basement finishing system are waterproof, but the sales droid I talked to says he didn't think one could put radiant under it.

Suggestions?

Gooserider


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## Highbeam (Jan 15, 2009)

I was in a home that had a lower level on a slab. He had set in the electrical grid element style of heaters within the thinset and beneath the tile. Very warm and comfortable. Obviously, the wiring would need to be installed using "wet" environment procedures but it was slick as heck and only used up a tile thickness in regards to headroom.


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## pelletfan (Jan 15, 2009)

There are several way to install a floor heating system.
Here a link from my bloging web page which explains the different systems.

http://www.finaltouchinteriors.com/...mments/radiant_flooring_heating_system_guide/

There are quite a lot of electrical systems available on the market, it's more a personal preference when choosing one.
and one of budget too.
If you go with a hydronic floor-heating system you should take a look at a system from Schluter

http://www.schluter.com/9_1_schluter_bekotec.aspx


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## Gooserider (Jan 16, 2009)

Thanks for the links Pelletfan, that Schluter stuff definitely looks impressive as a way to do the hydronics without getting too much added height.

Gooserider


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## pelletfan (Jan 16, 2009)

> Schluter stuff definitely looks impressive


Please note: I'm no sales person from them or get any commission from their sales.
Just happen to have used several of their inventions in my projects with real great success.
It is easy to work with their products and a lot of items are quite well designed. 
One other tip, they have a great customer support team.


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## d.n.f. (Jan 16, 2009)

I just installed Schluter in my kitchen (previous owner's tile job cracked everywhere).  It adds like $1.5 a square foot to costs.  Install was pretty easy.
I will use it in the bathrooms when I do them next.  Plus install that schluter stuff that goes up the wall slightly.  Stuff is supposedly great in showers too.
Don't forget you will need to buy some of that tape that goes with it.


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## pelletfan (Jan 16, 2009)

> I just installed Schluter in my kitchen (previous owner’s tile job cracked everywhere).  It adds like $1.5 a square foot to costs.  Install was pretty easy.
> I will use it in the bathrooms when I do them next.  Plus install that schluter stuff that goes up the wall slightly.  Stuff is supposedly great in showers too.
> Don’t forget you will need to buy some of that tape that goes with it.


Plumpers have to be a little bit educated that this is a good product. Especially when using their system in bathrooms. The Kerdi Drain system is perfect when using a natural stone for tiling. 
As any water which slips through the grout or stone drains away without any issues.


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