Home Improvement Asked by Kenn Sebesta on July 19, 2021
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?
Easymat is an acceptable 1/2" semi-rigid foam for installing tile. 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 with four sheets of rosin paper 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.
Correct answer by Kenn Sebesta on July 19, 2021
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.
Answered by Quoc Vu on July 19, 2021
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.
Answered by Lee Sam on July 19, 2021
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