0

We would like to insulate a concrete condo floor and for height purposes (already low ceilings as well as not modifying fire doors) we cannot add much material to the concrete pad.

Typically in this 12-story building the flooring (carpet, wood, or tile) is laid directly on top of the concrete, but this has led to too cold-floors in the winter. Thus, even a small amount of insulation would really cut into the heat loss and add a lot of comfort.

We've been examining adding a 1/2" layer of rigid foam insulation and then laying click-lock engineered flooring and/or porcelain tile on top. Despite some lengthy internet searches, we haven't found any reports-- positive or negative-- of this kind of approach. Almost all concrete floor questions involve basements, which require solving a completely problem approach because of water and moisture. Because the floor under us is a multi-story garage we're also not concerned about sound underneath.

I cannot immediately see why this would not work. While some foams compress, many foams are structural and do not. Standard pink and green rigid insulation foam can be gotten in compressive strengths of 100psi, which according to some sources is the same compressive strength as OSB. So from a compressive standpoint, the technique of concrete-->foam-->OSB/plywood-->glue-->flooring would seem to have no advantage over concrete-->foam-->glue-->flooring.

Are there any references for one way or the other? If not, can anyone share insight into what are the advantages to the extra complexity of adding OSB/plywood?

  • Hello, and welcome to Home Improvement. You're looking for the right foam to put under your flooring, but unfortunately "shopping" questions are off-topic here. – Daniel Griscom Dec 30 '18 at 2:50
  • I'm not quite sure why you would say that this is a shopping question. We're engineers looking for insight and references. There's certainly no desire to start a conversation about which brand is better. We've put in our research and discovered that either there is very little literature on this subject, but we're open to tips for improving the question. – Kenn Sebesta Dec 30 '18 at 12:42
  • Well, let's see what responses you get. – Daniel Griscom Dec 30 '18 at 17:03
  • Just a thought if you want tile in kitchens and bath can add heat mat tile over it. Good carpet pad good carpet to rest of areas. – user101687 Jun 18 at 8:46
1

Easymat is an acceptable 1/2" semi-rigid foam for installing tile. https://www.custombuildingproducts.com/products/surface-preparation/waterproofing-membranes-underlayments/easymat.aspx. It works very well and gives a very solid tile substrate.

Easymat is pricey and only sold by large rolls, though, so for tiling the areas under the cabinets[*] and in the closets we used XPS. This worked well, and these areas are subject to no repetitive loads which might knock tiles loose. However, one downside to the XPS is that the tile flooring sounds amazingly hollow underneath. This is in contrast to the Easymat, which does not echo at all.

For the clicklock flooring, we used 1/2" thick Kingspan foam (https://www.lowes.com/pd/Kingspan-Insulation-Common-0-56-in-x-4-ft-x-8-ft-Actual-0-56-in-x-4-ft-x-8-ft-R-3-Unfaced-Polystyrene-Foam-Board-Insulation/1000235443) with four sheets of rosin paper (https://www.homedepot.com/p/Trimaco-Trimaco-Easy-Mask-3-ft-x-166-ft-Heavyweight-Red-Rosin-Paper-36099/202040752) as a very sturdy underlayment. We arrived at 4 sheets because it was the point where even highly localized loads (me jumping up and down with my heel) did not damage the foam/paper sandwich.

The rosin paper is rated for permanent installation under hardwood flooring. It's reasonable to predict that since long-term loads from couches and furniture will be well distributed by first the flooring and then the rosin paper there will be no compacting of the foam.

[*] Tiling under the cabinets ensured that the cabinets are at the same height as the floor, plus it just looks nicer.

0

Just my 2 cents.

If you are doing a floating engineered floor over the foam, it might work if the foam doesn't flex and expand/shrink very much. You don't have to glue it to the foam as the click-lock mechanism keeps the pranks together.

For tiles, for sure, you can't do it over OSB/Plywood as it will expand/shrink and cause your beautiful new tiles to crack. You mentioned your floor gets cold thus I imagine you live in an area with fairly good temperature differential. Thus this problem will happen sooner rather than later.

I can't comment on the foam unless I know what type of foam you are considering. But I can say I have never seen any tile installation over foam. When it comes to tile, preparing the substrate is half of the work. We always tile over concrete, cement boards, or uncoupling membranes.

In addition, ensure the thinset can bond properly to the foam. Calling the manufacturer would be best.

0

No, neither ceramic tile nor wood flooring should be installed directly over rigid foam insulation. Both require an isolation board or slip sheet.

For tile, I’d contact the Tile Council of America (or now it’s called Tile Council of North America). They have “approved” systems designed for various situations, including waterproof and non-waterproof installations.

See: https://www.tcnatile.com/

Wood flooring manufacturers also have various systems approved for various installations. However, each manufacturer will have their own recommendations for their flooring. This is primarily due to what they’re made out of (they are composite materials) AND how they are made. (Think of GM...they build cars, test them and recommend how and when to service them.) Follow the manufacturer’s recommendations.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.