Laminate installation over concrete slab with radiant heat
I am looking to install laminate flooring over my basement concrete slab. We have hydronic heating run within the concrete slab. As well, there is 2inches of XPS and a 6mill poly VB beneath the concrete slab and heating tubes.
A couple of questions for the laminate flooring install..
1. Is there still a need for a 6mil poly sheet over the concrete separating the laminate from the slab? Keeping in mind there is already 6mil poly and 2in of XPS below the slab (all joints on the poly/foam board taped as well).
2. Is it advisable to use an underlayment between the slab and the laminate? The concerns are that a typical laminate foam underlay would hinder the radiant heat coming up from the concrete and secondly would there be concerns of chemical off gassing from foam underlay being directly in contact with the radiant heated slab?
Any feedback/guidance would be much appreciated.
Thanks!
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Replies
HI Rick -
You need to check with the manufacturer of the floor laminate. With some floor systems, the manufacturer is relying on a material between their floor finish and the floor below to act as a bond break, so that their floor "floats."
And generally, the foam layer that the manufacturer recommends or requires is thin enough that while it will have some insulating value, it is pretty minor (let's say the foam layer is R4 per inch and it's 1/4-inch thick that's R1 so yes, an insulator but not much of one).
Here is an example of guidance provided by a laminate floor company when there is a radiant floor: https://shawfloors.com/flooring/how-to/laminate/installation/laminate-over-radiant-heat.
Peter
This article may help.
https://www.buildingscience.com/documents/insights/bsi082-walking-the-plank
Hi Rick. I have the same concerns except that we're putting the laminate on the upper floor first. I'm trying to choose an underlayment. I understand that we need to follow the manufacturer's recommendations in order to not void the warranty, but that doesn't answer the questions of which underlayments when heated will not off-gas.
Also, I was thinking it might be nice to have something with a bit of give and had looked at some of the rubber underlayments, but am unsure of the R-value over and above the off-gassing.
Have you had any luck deciding? I'd be interested to hear if you made a decision based on your research.
Thanks,
Jen
When I put in my bamboo flooring, the Cali people recommended their own special underlayment. Their system is about a 1/8” foam sheet. I’m sure it has some insulating value, but I doubt it’s much, probably only a fraction of an R point. It does provide a vapor barrier when sealed with their tape, and it does provide a bit of give so the floor isn’t a foot-hurting level of hardness when installed over concrete.
They warn about using a too squishy underlayment with a floating floor too. If there is too much give in the underlayment, the finished floor can squeak and pop as you walk on it which is annoying.
Bill
Thanks for the info Bill. I've continued researching and you're correct about the R-value. Of the products I've been looking at they have ranged from .1 to .5. We're no longer as concerned about that.
In terms of comfort, from what you say, it's important to find the happy medium. Most are 1/8" or 1/16" so good to know that thicker is not better in this case.
At this point, I'm mostly concerned about off-gassing of the products. It seems as though most of them contain around 85% recycled tire content, but the remaining 15% is not "promoted". I'm just trying to make the best decision based on the fact that the product will be heated and I've learned this morning that the testing for Green Label Plus certification is done at room temp. I'm no expert on the science of this, but I do think that heat could potentially act as a catalyst to release more chemical content so am trying to figure out which one is healthiest in terms of indoor air quality. My research continues...
Thanks,
Jen
Jen,
You can get 1/8 cork (R0.4). Sqaures tiles are easier to deal with but rolls also work.
I've used 1/4" cork under heated floors which works but the slab temperature does have to be a bit higher because of the R value.
Yes, heating anything is going to increase the possibility of offgassing. Presumably you’re not going to be running the floor at unreasonably high temperatures though, so any increase in offgassing should be minimal. Also, the plastics most likely to offgass are those where the polymer has been modified. Usually this is done with plasticizers to make the plastic more flexible. The best example is PVC: PVC is naturally a rigid material (like in PVC pipe), so the pipe is very stable. PVC used in extension cords is modified to make it more flexible, and the stiffening over time is due to a gradual loss of the plasticizing compounds. Newer plasticizers are much more stable so this is less of an issue with quality modern products.
Polyethylene is usually NOT modified. Polyethylene is naturally somewhat in between being rigid and flexible. You may want to try to find polyethylene based foams for your underlayment if you’re concerned with offgassing. Cork may be another option, but I’m not sure if the cork is treated at all, and I’m pretty sure the cork won’t act as a vapor barrier.
Bill
The amount of heat we're talking about is really very low. Radiant floors are seldom warmed higher than the low to mid 80's. Well-insulated spaces need even lower radiant temperatures to keep warm. Your floors would get that warm if you just don't use the A/C in summer.
And I'd imagine a laminate floor in the sun would reach much higher temperatures than radiant heat below would induce in it.
We installed solid-strand bamboo over concrete using an underlayment called Delta FL. It's a hard polyethylene (sp) bubble sheet (about 1" diameter dimples). It's nice because the dimples leave a slight air layer between the concrete and the flooring, which has some insulative value and also a place for water to go when something spills. We might've used polypropylene foam between the Delta and the bamboo, can't recall. To my knowledge polyethylene and polypropylene are not outgassers. I'd be more concerned about formaldehyde from the glues in the laminate/engineered floor.
An alternative might be ceramic / porcelain tile.
Thanks everyone for your responses. It helped me to make a decision on which product to use. As mentioned above considering the in-floor heat temp is not much higher than typical room temp, I'm less concerned about off-gassing considering the product has been tested and certified.