Hydronic floor heating – vapor barrier or not?
seangaug
| Posted in General Questions on
Climate zone: 3b (Northeast BC, Canada)
I am installing a hydronic radiant floor heating system on top of a subfloor. There is an unconditioned crawlspace underneath the subfloor. Should I put down a poly vapour barrier or tar paper before I put down the radiant floor heating?
When I tore up the old floor back to the diagonal subfloor there was tar paper on top of it and then the first layer of flooring. I have since added 3/4″ T&G OSB as a new subfloor without any paper or poly between it and the diagonal subfloor.
The original flooring layers top down:
laminate
luan
linoleum
1/4″ mdf
tar paper
1″ diagonal fir subfloor
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Replies
>"I have since added 3/4″ T&G OSB as a new subfloor without any paper or poly between it and the diagonal subfloor."
At 3/4" the OSB subfloor meets the NBC definition for "vapour barrier".
Are the joist bays filled with insulation?
Is the crawlspace vented to the outdoors? If not, is there a vapor barrier at the crawlspace floor?
You didn't mention what you plan on putting over the radiant or are you using radiant panels eg. tubing in plywood with channels w or w/o aluminum fins.. Until we know that, it's hard to answer. The reason the tar paper was put between the diagonal and mdf was to prevent friction which could lead to squeaky floors. You skipped that this time around, so once you start heating the floor and it starts expanding and contracting you may hear things.
Thank you for the support and for your comments.
Are the joist bays filled with insulation? yes
Is the crawlspace vented to the outdoors? no
If not, is there a vapor barrier at the crawlspace floor? yes
The radiant floor will be as follows bottom up:
3/4" OSB subfloor
aluminium heat transfer plates
1/2" PEX-AL-PEX set between plywood with channels
1/4" plywood
vinyl planking
Thanks for the explanation on the tar paper. I hope this doesn't become a major issue. I have glued and screwed the new subfloor down so hopefully this will help cut down on the noise.
I would try to put the transfer plate on top of the channeled plywood in contact with the 1/4" if possible (or is that your plan) ------u------ Snap the tubing into the channel then cover with the 1/4" Remember wood is more of an insulator than a conductor.
An unconditioned crawlspace should be well-ventilated and the floor above it should be sealed in the same way as a wall in your climate. The only change with the hydronic heat is you want it better insulated because the temperature will be higher and thus the potential for heat loss is higher.