Should I use a subfloor for a finished basement's floor?

Question

We are refinishing our basement and have not yet decided what to do for the floors. Part of the basement will be tile, and we are all set. However, the rec room side is going to be carpet. The basement is dry, and we have never had any water or moisture issues.

Some research has said to simply lay carpet like normal, with a thinker pad on the concrete. While OK, I am worried a little about the coldness, a vapor barrier, and the comfort level (too hard on concrete). One carpet guys said they make special pads that are vapor or moisture proof and will not have mold issues and are made for concrete floors.

Other people has said to lay .5"-1" foam board down, and then install plywood on top of that. That would help to insulate, make it feel like a normal floor, and provide a good moisture barrier) But this would cost more in labor and materials, and cut into the height of the room (it is 7'8"). And although we have not had water issues, heaven forbid if we did, this would be a major pain to rip it out.

What has everyone else done? Any recommendations?

Answer 1

I just recently finished my basement project. I spent a lot of time scouring the web and grilling friends and co-workers about their basements to gather information to try to make an informed decision on this very subject.

Here are the options I considered:

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Carpet tiles directly over concrete

PROS

• cheap

CONS

• cold feet
• hard, unforgiving floors
• Potential for condensation/mildew, even if floor is mostly dry

VERDICT

• I couldn't find a tile with a padding thick enough to make the floor even close to comfortable in a midwestern US winter

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Traditional carpet and pad directly over concrete

PROS

• Pretty cheap
• Many choices of carpet and padding thicknesses available

CONS

• Floor is still much harder than wood subfloor
• Even thick padding can still leave the floor a bit chilly
• Potential for condensation/mildew, even if floor is mostly dry

VERDICT

• Thick padding can help the floor feel less cold, and less hard, but it's no match for wood, especially if you have a kid's playroom or a workout room in the basement
• It seems like asking for moisture/mildew trouble to not allow air circulation between concrete and carpet

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Rigid foam insulation under 5/16" plywood subfloor

PROS

• Cheap
• Good R-value to provide insulation from cold
• Feels almost as warm and soft as a regular subfloor

CONS

• Opinions vary about how long the foam will last before breaking down
• Installation instructions vary wildly (some anchor directly to floor, others anchor through wood bracing, etc.)
• Opinions vary about how much air circulation the foam would allow

VERDICT

• Although it doesn't seem like a terrible idea, there just wasn't enough information about this approach to make me feel comfortable trying it

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DRIcore-style subfloor tiles

PROS

• Dimpled underside allows excellent air circulation over concrete
• Feels almost as warm and soft as a regular subfloor
• Most come in 2'x2' tiles so there are no 4'x8' sheets to lug around
• Easy install, much like a "floating" hardwood floor
• Nothing anchored into the concrete

CONS

• By far the most expensive option
• Each 4 sq foot panel is about $5.50 [as of 2016] USD

VERDICT

• I had a fairly large amount of floor to cover, and this was just too expensive. It would have approached 20% of the total budget for the project.

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Dimpled underlayment under 5/16" plywood subfloor

UPDATED March 2019

The Platon underlayment I used years ago seems to be hard to find these days. Home Depot currently offers what appears to be a similar underlayment product called DMX 1-STEP, and others may be available from other manufacturers.

PROS

• Dimpled underside allows excellent air circulation over concrete
• Feels almost as warm and soft as a regular subfloor
• Much cheaper than the DRIcore tiles, because the Platon is purchased separately in large rolls

CONS

• More difficult to install than probably any other option
• 4'x8' plywood subfloor is no fun to lug around
• Requires the subfloor to be anchored to the concrete

VERDICT

• Although it required more manual labor, the cost was less than 10% of what it would have cost to use the DRIcore tiles
• I still got it done in just a few days, with some help moving the plywood
• I used a hammer drill and Tapcon concrete screws to secure the floor
• My basement floor is as warm and soft as any other floor in my house, and it didn't cost an arm and a leg

Answer 2

If your basement is really dry as you suggest, carpeting directly on top is fine.

To test: Take a 1x1m sheet of plastic (garbage bag would do) and tape it to the floor making sure it's sealed all the way around. Leave it there for 24h at least and see if moisture appears at the bottom.

If it's bone dry, you should be OK. We renovated our basement and based on the carpet installer's recommendation, went with a really good quality under-pad with berber carpet on top.

You would never say that it was on concrete. The carpet is great under your feet and not cold at all.

I believe the biggest factor is moisture. If it's not a dry basement, I would probably put a sub-floor in. I don't know if a moisture barrier is actually "good" as it could actually trap moisture under there that would accumulate over time. DryCore (subfloor) for example has channels underneath that eventually vent out on the sides. All concrete will release some moisture over time and I suspect a "breathing" carpet is probably better then something with plastic barrier with a 100% seal.

Answer 3

I grew up with a furnished basement that only had foam carpet pad covered with carpet. The cinder block walls were coated with UGL drylok and it was lit with flourescent lighting. The foam/carpet worked very well, no drafts, no wet spots, was perfect to lay on. Didn't need to go as far as a subfloor and I live in a harsh winter climate.

Answer 4

Newer technology:

(a) "Floor Comfort" with an R-4.5 rating, moisture and vapor proof and only approx. 1/8" thick, so no issue with existing doors

(b) DryBarrier (with raised channels underneath for water drainage) 3/8" thick, was not able to find out R rating.

Answer 5

I definitely wouldn't lay carpet - after any water seepage or spillage, it stinks. And, carpet holds debris. DriCore is just too $$, and am now looking at possibly just an underlayment of foam with laminate directly over top. Or, you could put a plywood subfloor down and finish it like a wood. Haven't finished making up my mind, but am currently researching detla and thermaldry. The thought of screwing anything into concrete makes me uneasy.

Answer 6

I went the super-cheap route: We cleaned the floor and then stained it (concrete acid stain) and then gave it a coat of sealant.

It's not for everyone from an aesthetic POV but we like it. It was inexpensive and no worries about mildew or moisture.

Answer 7

We laid thin pad and carpet on a concrete floor in KY basement in 1978. No issues other than carpet style is out if date. Pulled a section for room add and no mold or problem. If dry, personal preference.

Answer 8

What about cork tiles, they should hold cold back.