AFAIK the best-practice for applying insulation+vapour barrier in cold climates is:

inside -> inside wall -> vapour barrior -> insulation -> outside wall (exposed to the elements).

If you put the vapour barrier between the insulation and the outside wall, you could risk vapour reaching the outside wall resulting in condensation and mold.

Why am I then, here in my cold climate country, seeing a lot of new buildings with insulation boards with foil facing outside?

The foil is probably there to give radiant insulating properties, but it's also a vapour barrier.

Could it be that there's also foil facing the inside and thereby eliminating the condensation issues?

  • 1
    You can probably find your answer here: buildingscience.com/documents/digests/…. This is one of the better references I've come across for insulation and vapor barrier situations.
    – SteveSh
    Dec 11, 2021 at 17:03
  • And just a further piece of info. When I had a major renovation done to the house, the builder followed the same arrangement you described - with insulation boards with foil facing outside on the outside of the house.
    – SteveSh
    Dec 11, 2021 at 17:06
  • Oh, and I'm in the mid-Atlantic region of the country.
    – SteveSh
    Dec 11, 2021 at 17:12
  • tyvek is a perforated building wrap. Without the perforations that aren't visible to the eye you'd have a vapor barrier on the exterior. tyvek is the typically exterior house wrap in my cold climate area. possibly the foil faced insulation has perforations? Dec 12, 2021 at 8:55

1 Answer 1


I think I've found the answer myself.

The following insulation board (not that specific brand) is an example of what I've seen on several construction sites where new apartments are being build:



In the PDF document it is specified that there's foil on BOTH sides which eliminates the condensation issues:

"The facings Kingspan Thermawall® TW50 is faced on both sides with a low emissivity composite foil, autohesively bonded to the insulation core during manufacture. This reflective, low emissivity surface improves the thermal resistance of any unventilated cavity adjacent to the board."

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