Cork Floor Over Radiant-heat Basement Slab

canadianwood

Hey guys, longtime lurker first-time poster, I am not going to ask how much something costs in my first post
I am a GC in Edmonton, AB with most of my experience in carpentry.
I have a question for you flooring experts out there, I am finishing a basement for a client who wants infloor heating. We'll be pouring gypcrete to cover heating tubes/levelling/etc.
My question is: does anyone have any experience with laying cork planks (floating-type) onto heated slabs(below grade)? I would like to stay away from laying a vapour barrier due to obv mold issues, I will obviously need some sort of vapour retardant (I think..), but what will work best for cork?
Does anyone recommend building a sleeper system, sheet it, then adding a vapour retardant underlay (eg quiet walk, etc)??

Thanks guys,

genecarp

I have never done radiant under cork, check with the manufacturer of the cork, let them know your intention. I would think the cork would insulate, and not allow the full heat output into the room. G

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canadianwood

Manufacturer is in Portugal and has no North American contact, distributor locally has no info on this particular scenerio. This is a bit unique and the flooring subs I deal with don't know, they said that since its a wood product then moisture control is important, but they don't know to what extent...

Jeremy E

I've been researching cork flooring for my own home, and my first thought was the same as Gene's with regard to it's insulating properties.

Jeremy E

Here are some numbers* (R-value):

1" cork board = 3.33
1/8" cork tile = 0.28

for comparison...

linoleum or rubber tile = 0.05
carpet w/ foam rubber pad = 1.23
3/4" hardwood flooring = 0.68

*from the Sequoia Press Pocket Reference, 3rd edition

olzo55

i've put cork on an unheated slab using the manufacturers vapor barrier. how is a vapor barrier different from a vaapor retardant in your opinion? also, with a sleeper system you are further insulating the heated floor from the cork so why would you do that? just use the maufacturers products. they made them for a purpose and you'll be getting their warranty. finally, the product should have a manufacturers website/email/phone number. why not directly shoot them a message and give us the scoop?

astor

Check with TORLYS.
www.torlys.com

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canadianwood

A vapour retardant is a material that slows or limits the passage of moisture through it, while a vapour barrier acts to completely stop it (as far as it is capable of). A good way to think about this is house wraps (Tyvek or building paper) are vapour retardants, these products are semipermeable to water vapour and act to prevent moisture from accumulating within the building envelope. Polyethylene (like we use in Canada) is a vapour barrier, I won't go into details but suffice to say that this is used to STOP moisture from passing through.
So, the reason to use a retardant is to allow the slab and walls to "breath" while still limiting the amount of moisture passing through it. This is a basement built atop a clay lens that keeps water, thus the basement, in this case, must allow some moisture permeability without compromising the interior finishes. Otherwise we may have serious moisture/mold issues.
I should have been clearer on the options:
1) radiant heated floor with cork over top (need some sort of vapour retardant)
2) polystyrene floor with 2x 5/8" plywood and cork layed directly on top of that.

Kengineer

If you look at the floor covering R-Values listed by the Radiant Panel Association, you can see that the 1/8" cork is a little less than for 3/8" engineered wood.

Any resistance you put over the radiant heat will reduce system efficiency, driving more heat down into the slab and less into the interior space. That being said, the values for your thin cork are considered acceptable over floor heat in the industry.

The biggest problem here isn't the floor covering, it's the slab you are on top of. Your heat loss to the slab is going to be huge, regardless of what you use for a floor covering. If at all possible, find some way to insulate UNDER your heating tubes. Are you using any insulating boards designed for hydronic systems? Or maybe float the whole new system on rigid Polystyrene planks? The improvement to your system efficiency would be considerable.

Archania

Out here in CA, tons of Eichler houses (Flat-tops) had cork floors and radiant heat. I have replaced some, with either cork or just some laminate wood flooring. You cant use the plastic sheeting. The stuff you use almost looks like packing material, about an 1/8" thick. Its really just a pad. But for sure check with the manufacturer, because they will tell you exactly what to use.

canadianwood

I understand that there will be considerable heat loss thru the slab. I like the idea of insulating over the slab, then laying heating tubes; however, I don't know how strong the gypcrete will hold over the insulating boards, specifically in heavy traffic areas. I am concerned that 2" of gypcrete will eventually crack and loosen when poured over the insulating boards, I could pour a thicker layer (3-4") but then I'll be too high in some areas of the basement.

Hmmmm, I don't think I'll be able to guarantee this floor at all. NO WARRANTY!

astor

I suggest calling TORLYS -I posted before, but did not have much time to write more.They have a Vancouver office and I am sure will give you technical info.

here are couple links may help
http://www.radiantpanelassociation.o...cfm?pageid=145
for FAQ's
http://www.radiantpanelassociation.o...cfm?pageid=438

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hawaii

From my expierence allways follow the rule first.
Find the floor that you like ask the manufacturer if they recomend to put it over radian heating system then ask them details.
Cork is usually very stable floor and you can allways take chances but if you want to do it professional.
Ask manufacturer.

Good luck.

canadianwood

Ok guys, problem solved. Maxxon makes a vapour retardant that coats onto existing slabs for gypcrete overpours. It cuts vapour emissions to a level that is deemed acceptable as a vapour barrier here in Alberta. So, we are doing the 1)vapour retardant coat, 2)heating tubes, 3)gypcrete overpour 4)cork flooring with no underlay (planks have 1/8" cork underlay on them)

Thanks for all the advice, I agree fully with the loss of heat from under the slab, but in this case, we are making concessions where we can, efficiency is down, but clients get everything they want.

Cheers,