What subfloor in new construction basement?

8 years ago

So we are in the process of building a new home.. When we first began building we had all intentions of leaving the basement unfinished.. Well as time went on we decided to start the process.. We have since had the framing and electrical completed in the basement.. One of the things I am trying to decide on is what subfloor to use.. We have a very large ceiling in the basement.. I believe that it comes in just over 9ft.. The only issue (if it is one) is that the stairs are already installed.. I was looking around online and saw that most people do 1 of 3 things.. 1) They install 2x4 sleepers with rigid foam in between, 2) they install products like Dricore, or 3) they put flooring directly over concrete.. I am trying to decide what the best method would be to use on the subfloor.. Part of the issue is that the HVAC is installed in the basement and while I can leave the utility room as a concrete floor I wanted to avoid having a "step" or large difference in height.. We are coming close to finishing the build but at this point the only items installed in the basement are the sump pits and the HVAC furnace.. Other than that we are still completely wide open.. We have 1400 square feet to work with.. We have calculated that we could do the dricore panels but would end up spending 2500-3k just for the panels.. I would imagine that 2x4 sleepers would be much more cost effective, but would we have issues with the stairs that are installed as well as the furnace being already in? Also the plumbing for bath is roughed in already..

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worthy

8 years ago

last modified: 8 years ago

"2x4 sleepers with rigid foam in between"

Any wood must be on top of the XPS (extruded polystyrene) foam, otherwise moisture moving upward through the slab, or as a result of small leaks or floods, will promote mould and rot.

Besides Dricore or equivalents, alternative acceptable approaches would be a layer or two of 1/2" plywood above the foam. Or a plastic air gap membrane such as Delta Fl followed, depending on the final finish, by plywood.

If you are using tile or stone, no subfloor is required, though a crack isolation/prevention membrane such as Kerdi would be advisable.

I have often used low-pile synthetic carpet directly on newly poured well-drained concrete with acceptable results.

In all cases, mechanical dehumidification is necessary to keep rh below 50%.

See Building Science Corp. publication BA0-309 for further information.

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Comments (6)

Vith
8 years ago
I commend you for doing the right thing and insulating the floor. You will appreciate it later. First make sure you don't have a moisture problem with the floor by taping plastic down to it. If condensate forms underneath then you should waterproof the floor first, I recommend oil based watertite for this if needed. Then you can do XPS rigid foam with plywood on top of that. You don't need sleepers, although I have seen it done also, would probably use treated if so (the newer treatment is not as bad as the old CCA which was bad to put indoors). Predrill and pre countersink holes then drill in countersink tapcon screws.
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njbuilding143
Original Author
8 years ago
Worthy and Vith - Thanks for the input.. The reason I was thinking of sleepers was for leveling purposes.. The floor is pretty level but I occasionally "feel" a slight difference.. Have yet to get down there with a large level to see exactly where it falls... I was considering doing the 1inch XPS all around on the floor and then doing plywood over that.. I am just starting to think about the floor height now that doorways and such have been formed and the stairs are in.. I noticed they left a 1 inch gap between the bottom riser and concrete floor.. so the 1inch XPS would fit perfectly and line up.. However once I add the plywood and then flooring it would probably add another inch or more depending on the thickness of subfloor..
User
8 years ago
last modified: 8 years ago
If you add any sub flooring and flooring tang adds up to more than an inch in height you'll HAVE TO REFRAME the stairs. After you accept this reality , then you can begin to select what you're going to do. The plumbing in the bath shouldn't be an issue no matter what you end up doing.

If you're set on not re doing the stairs , your options get a bit more limited especially with a sub floor. Dricore is out as its nominally an inch thick itself and so is 2x sleepers .

Kerdi IS NOT for basement floors ! Ditra is for that.
njbuilding143
Original Author
8 years ago
Thanks for all the input.. After thinking it over we have decided we are going to tile the basement.. My father-in-law said he would do it for us and recommended going with tile.. We figure it durable and the most resilient flooring... So we are going to do a wood look tile and throw area rugs down to warm up the space..
worthy
8 years ago
last modified: 8 years ago
"Kerdi IS NOT for basement floors ! Ditra is for that."

Thanks. Right link, wrong name.

What subfloor in new construction basement?

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Vith

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