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Basement sub-floor

To do the basement sub-floor, I’m using a product called Delta-FL, which I picked up at Rona. It’s basically a big roll of dimpled plastic, which sits on top of the basement slab and acts as a vapour barrier, adds an air gap that helps insulate the floor, and also raises the floor up off the ground to avoid water damage in case there is a tiny amount of water. On top of this, I’m putting 5/8″ OSB, and then using tap-cons to secure the OSB to the floor. Although you can put some flooring (eg, laminate) directly on top of the Delta-FL, I was a bit worried about doing that since there are a couple places that aren’t totally level – the OSB lets me even them out and get very close to perfectly level.

Once very nice thing about this flooring system is the minimal height it requires. Since my basement is a bit short (7′ 3″ unfinished floor to joists, 6′ 6″ unfinished floor to heating ducts), I wanted to keep as much of that as possible. The total height is just over 1″, so it really isn’t bad.

I have a 12″ piece of vapour barrier plastic underneath all the exterior framed walls. I called the manufacturer of Delta-FL to check what the best way of dealing with that was, and they advised me to tape the barrier directly to the Delta-FL, forming basically a complete seal around the walls. I used tuck tape to do this, and tape all the pieces together. I had to cut a couple holes out to fit the floor drain, toilet drain, and a jack post in the middle of the basement.

I worked in sections, putting a couple strips of Delta-FL down, and then laying the OSB on top of it, and connecting the grooves up. Once I had a couple pieces of OSB down, I would take some tap-cons and secure down the first row – I found it was much harder to get the tongue and groves of the OSB to connect up, if one of the pieces was already screwed down. I left 1/8″ gap between all the pieces of OSB, and the exterior framing. I was also careful to stagger all the sheets of OSB, so all of the ends are offset, forming stronger joints.

For the floor drain, I just made some careful measurements and then used my jigsaw to cut out a hole.

The toilet drain happened to line up with the edge of a piece of OSB, which made cutting the hole much easier. As you can see above, I also made sure the jack post was on an edge, so I only had to cut a U shape out of one piece – the other just butts up against the edge.

Though I don’t plan on doing anything with the crawlspace floor, I did put the sub-floor into the door opening, to make it easier to put the door on, as well as to hide the edge of the floor from the finished basement.

Today it is -10° Celsius out, and the surface temperature of the unfinished floor in the crawlspace is 9°, while the surface temperature of the OSB is 14°. The basement walls are still uninsulated, so this may not be overly conclusive, but it does show that it makes a difference.

Update: My girlfriend says “the basement floor feels much warmer now”. I guess that’s conclusive.

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  • That flooring is neat – and a great idea to raise the floor slightly.

  • I’ve been looking at the Subflor product but at more than $7.00 a square (2×2) it’s looking a little expensive. I’m thinking that your solution is probably more economical and accomplishes the same thing, with a little more work involved.

    Any idea what the cost of your sub-floor was per square foot?

  • It ended up costing me about $0.83/sqft. I bought 30ft rolls of the Delta-FL, which works out to ~$0.50/sqft. I think it is slightly more expensive if you go with the 4×8 sheets of Delta-FL, but I would recommend the rolls. It’s easy to cut anyways, and it involves less taping when you can do long runs with one piece.

    The lowest I’ve seen for Subflor/DriCore ($6.50 ea on sale), is still twice the price, at $1.63/sqft. I’m really not sure it is that much easier to install – I did almost all this floor on my own. The hardest part was just moving the full sheets around to cut and position, which is not hard.

    There is another benefit of Delta-FL – that it forms a complete barrier. With DriCore/SubFlor, there is a small gap in the plastic between each tile, so I don’t think it serves as a vapour barrier.

  • Thanks. That’s very helpful. I’ll do some checking at my local Rona to see if they have Delta-FL.

  • tim morey

    I finished my basement a two years ago, i put my basement in 6 years ago and had no water problems. Now for some reason the water table has changed or something. I have a sump pump in the basement with a tile around the outside perimeter of my basement addition on 2 sides. Water is coming in on all 4 walls and the floor do to the water table being so high. The water table went up Late January of last year and went down around mid march, Yesterday i started getting water in the basement again. i never get any more then about 1/2 of water over the floor since i have the sump pump. What i was wondering is if this product would work or if i would have Moisture or Mold problems.
    Any help would be appreciated.

    Thanks Tim

  • There shouldn’t be any moisture problems in the actual floor, since the flooring is a vapour/moisture barrier. With a small amount of moisture, it should dry fine because of the air gap.

    However, if you have a large amount of water (eg, flooding), so there is no longer an air gap, I could see that being a problem, possibly leading to mold since it may not fully dry out. In fact, the install instructions specifically say it’s not to be used as the only protection for flooding.

    Personally, I would think it would be better to find out where the water is coming from and fix that. This can protect against moisture that naturally comes through a porous material like concrete, but running water is a different story.

    If there are cracks in the foundation, or other holes, plug them up. Consider improving the drainage around the house – adding some dirt to raise the grade around the house, and adding extensions to your downspouts can do wonders.

    If it is just water coming up through the sump hole, then maybe you need a bigger/second sump pump (don’t forget to have a battery-powered backup pump, or some other way to handle water if the power is out). You might also need to investigate improving the drainage around the outside of the foundation, although this is obviously a lot more work and a lot more costly.

  • tim morey

    I have a 4′ drain tile around the inside of my basement and it goes to a sump basket. What i’m seeing is that for the second year in a row after 8 year of a dry basement the water table has raised and when it gets above the tile there is alot of pressure. I have no cracks in the basement floor. The water is coming in around the walls between the Basement walls and the slab. There is so much water pressure now that i have a pin hole in the basket and it is spraying water. The water does drain to the sump basket as well. It’s like i need to line the basement with a pool liner. the water isn’t coming from the out side. Do you have any other ideas? The basement is only about 800 square feet..

    Thanks for the response though.

  • Rob Marchand

    Quick question for you. I was wondering if you did anything special for the floor drain – does it sit below the level of the Delta-FL and the OSB floor? Or is there a special cover/flange that you are using?

    I am doing something similar, and have been trying to figure out how to handle the floor drain, which is out in the open area of the floor.

    Actually, looking more closely at the pictures – is the floor drain aligned with a floor drain in the slab?

    Thanks in advance!


  • Rob: The floor drain is just a drain in the slab. I cut a hole for it in the subfloor, and my intention is just to put a drain cover on the hole in the finished floor. I had thought about trying to find a flange, but then I realized if there is water underneath the subfloor, I still want it to drain.

    I’m not sure if it’s the best way.. and in fact, the drain ends up in a weird spot in the room. I think it’s important though that it’s accessible (in case it needs cleaning out or whatever), as well as usable (in case there is a leak in the washing machine or sink or whatever).

  • pete

    my hot water tank burst on me a few weeks back.. I had a regular sub floor that raised my floor a few inches. when they removed the floor I found that I have 3 holes in the middle of my basement (by holes I mean pipes). One is the sub pump I believe as I’ve noticed when it rains, some water is in there and then disappears (it’s about 2 ft deep, and the water doesn’t come anywhere close to the top).. how can I do the above floors, and cover these, and then put floating floors over? is there any tricks?

  • bob clarke

    i have a dirt floor in my crawl space ..what can i use .. would it be the Delta-FL then some pressure treated 2×4 for a sub-floor or what other combo would you suggest..thx

  • Kris

    Hi there Greg,

    I made the same decision as you in regards to the dimpled plastic roll covered with OSB. I’m in the finishing stages of my remodel, and I’m desparately trying to figure out what I’m going to do with the drain. Could you email me some pics of what you did to finish off the drain? Thanks so much


  • Kris: Take a look at It really will depend on what you are using as flooring. I basically just wanted access to the drain in case it ever gets clogged or something.

  • Chris S

    What was your spacing of tap screws ? Any concern that this would puncture the “vapour barrier” effect of the dimpled membrane?

  • Chris: I initially started putting about 8 tap-cons per sheet, but that was nowhere near enough. I ended up using probably double that, basically making sure the corners and edges were secured, and then a few in the middle. I then would walk over them, and anytime I heard the click of the DeltaFL against the concrete, I put another screw in. I probably spent a couple weeks continuously adding new screws as I found new spots, but I figured that it was better that way than finding them after the carpet was done and I couldn’t fix it.

    To be honest, I wasn’t really concerned about the moisture: the basement is quite dry. The proper way to do it though is to dip each screw into caulking before screwing it in, as it’ll then form a vapor-tight seal around the threads.

  • John

    I have an unfinished basement and would like to just lay down used but very good conditioned carpet with underpad that came from my upstairs living room when I changed it to hardwood floors. My question is can I just lay the carpet and underpad directly on the concrete basement flor or will that trap moisture and creat mould? If so, would you recommend using the Delta FL barrier 1st then lay the underpad and carpet and will that prevent mold?

  • Rod


    did you use special DELTA FL tape for seams between
    DELTA sheets or you join them all by Tuck tape ?

    Thank you

  • John: Because carpet is breathable, it will not trap moisture. Carpet directly on slab works, but it is quite cold on the feet, unless you have insulation underneath your slab (which is unlikely unless your home was built in the last 5-10 years, and even then not everyone does this).

    Rod: I just used tuck tape. I couldn’t find the special “delta FL” tape they were referencing, and didn’t really see how it was any different anyways.

  • Nice sub-floor installation. For an easy to install basement floor, you can also use interlocking floor tiles made from impact polypropylene. They have grooves underneath so the tile is raised and it allows for air passage. It is a faster and cheaper installation option that what you described. They are many options available in the market and normally sold for a garage floor use. A quick Google Search will give you many options.

  • Jim

    Hi Greg,

    The floor looks great. I’ve read that you can frame right on top of the Delta-FL, however I’ve also read on some sites that this is a bad idea. What method did you use/would you suggest? Thanks.

  • Jim: Thanks. I don’t see how framing directly would cause a problem. I put the OSB down and then framed on top of that. This means my bottom plates are just screwed into the OSB, which was pretty easy to do.

    If you were to frame directly on top, you’d need to secure the bottom plate to the slab somehow, and also be careful not to overtighten if using screws as it may compress the deltaFL too much, at worst losing insulation value or causing the floor to be uneven.

    If you’re planning on putting OSB or plywood down, I would just do that first then frame on top. If you’re going to directly finish on top of the deltaFL (eg, with laminate or hardwood), then I don’t see how it would be a problem.

  • Bob

    I’f laying tile on the woods it sturdy enough to prevent joints from cracking?

  • Ross

    hello all…

    I’m not sure if someone mentiond this, but instead of paying the higher cost for a roll of Delta FL, I used Delta MS foundation wrap (its brown in colour).. it was way cheaper than the FL and I couldnt see the difference… I was at the home depot with my friend and while there a Delta rep was also on site… he was pushing the Deltal FL, but we started asking him why FL instead of the much less expensive MS… he also couldnt find an answer for us, even when we took a roll of FL to the building section and placed it up against the MS foundation wrap… both say they will never break down, both provide moisture/water protection, both are non polutting and both are non toxic… the compression ratio is very close as well… save your money, go with the MS… it was a breeze to install…

  • Nick

    Ross: I was going to go the same route and use MS but decided to call Delta directly first. I was told that there is no difference except that FL is made from new material and MS is made from %60 recycled materials. He said it smells bad and that the smell would never go away… if you can live with the smell go for it. I brought a roll of it home and it reaked! I guess that’s why its meant for foundations. HD carries a product called Platon very similar and comes in rolls 6′ x 65.5′ Its a foundation wrap and can also be used for floors, it must be made from new materials compared to MS. I got a good deal on Delta FL that’s why I went with it, next choice would have been Platon.

  • Matt

    does anyone know if I can install the subfloor and then install the framing on top of the plywood or do you have to frame the room first then the subfloor? thanks in advance

  • matt reg

    I have a quick question. If I’m using delta fl with tg plywood ontop before laminate do I need to screw the plywood down to the concrete??

  • Looking for Answers

    In reading your article, you noted floor temperature and air temperature during installation. What was your final room temperature differential from the rest of the house? In my house the basement is 7 deg cooler than the rest of the home.

  • Rebecca Harriss

    I am also at the drain dilemma, I’ve installed the delta subfloor and plywood and our drain ends up being located in the newly built bathroom. I also I want access to it without interferring with any floods from the neighboring laundry room under the subfloor. I see on your laminate installation that you have cut out for the drain but I can’t see from the photo how the subfloor plays into the drain or how you may have water proofed the drain. From what I can see and whithout explaination, if water was to get between the laminate and the green foam there could be a future issue.Can you give me some more steer? Thanks in advance.

  • Thanks for this share! This is a great way to prevent moisture from accumulating on the floor. Although it might not protect from huge floods, I still think it is one great measure of protection for smaller ones. This is a great post! Thank you for sharing!

  • Andy in Ottawa

    Your setup looks good. Thinking of doing the same in my basement.
    Now that it has been a few years, have you been tracking the floor temperature vs crawl space vs outside temp? Any issues with mold. Wouldn’t tap conning into delta break the barrier seal, allowing moisture though, up screws?

    What city are you in, so that I can determin comparibillity to my situation?


  • John Decker

    This is a great article. I am finishing my basement right now and it has been a long process. I really wanted to make sure it is properly ventilated and to have a Dehumidification system installed. It is important that the climate is controlled because my kids will be playing down their a lot.

  • Nice photos ….in fact very informative post thanks

  • Quite impressive post thanks for share……………

  • Thanks for share …..keep it up………..

  • alan

    Finishing Videos teaches you how to finish basement.If you are looking for
    basement finishing cost then basement finishing videos would help you.How to frame a basement
    to how to finish a basement , such questions would be solved.,,,,

  • alan

    Finishing Videos teaches you how to finish basement.If you are looking for
    finishing cost
    then basement finishing videos would help you.How to
    frame a basement to how to finish a basement , such questions would be solved

  • nes711

    I am putting down resin paper then 1/2″ OSB 1 1/2″ tapcons how far do I need to drill down

  • Swen0277

    I am planning to do this same thing. Thanks to this info. I have a question however. Would you ever do this without t and g flooring? I’d like to use 7/16 osb because of clearance issue with my doors – I’m doing some work in backwards order. I don’t think I can get 7/16 t and g osb because it’s too thin. I was thinking about making my own by doing a ship lap on the osb and then screwing the seems together. Does anyone have thoughts on this? Would i be better off just using the tap cons on the edges and trying to ensure the seams are even? Thanks for any help out there!

  • Ian

    Is using the landscaping paper a good beneficial way or can I just put another tap on in the area of the clicking noise?