GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Basement floor vapour barrier

sunstone | Posted in General Questions on

Location-Toronto, Canada Zone 6A (why doesn’t your zone map include Canada?)
A basement concrete floor with radiant floor installed but with no vapour barrier (R10 foam installed to secure the tubing but it is not continuous at the waste drainage lines)
Would it be advisable to put a vapour barrier on top of the new concrete floor before any flooring? Or maybe just leave it, let it breathe

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Dana Dorsett | | #1

    There is a map that covers Canada & US, but it's not very accurate:

    If you look at the most recent 25 year data history, Toronto is on the cool edge of zone 5, defined as as 3000 - 4000 HDDC (base 18C): (scroll down to the bottom for annual HDD)

    If the foam is the pink or blue stuff, at 2" it already meets the NBC definition of vapour barrier. If the only discontinuity is at the drainage lines (which are also impermeable to water) the total amount of area is small. That said, concrete doesn't need to "breathe", it is not damaged by moisture even when saturated. (They build bridge foundations out of it, after all.) If installing a wood subfoor or other flooring susceptible to moisture damage a layer of 6 mil polyethylene is pretty cheap insurance, even if not absolutely essential.

  2. sunstone | | #2

    Thanks Dana, for the charts,maps and data. All bookmarked under 'EE'
    After a concrete floor poured, is it advisable to delay framing of walls or any other steps. Flooring eventually or spray foaming of the walls (rubble fdn with dimple mat cover to ground level

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |