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Advice on rigid exterior roof insulation in the Netherlands

kabouterhout | Posted in Green Building Techniques on

Hi everyone.  Very long time lurker, member and reader of these forums but this will be my first post.
As stated in the title I live in the Netherlands but I am an American carpenter by origin and am remodeling/rebuilding my own house. Its very small by North American standards, about 450 sq ft with a small second story loft. Ceilings are all open thus cathedral so to speak.
The climate zone here is probably comparable to a 4a or 4b. Generally pretty mild, similar to Seattle with a more humid summer. Nowadays it only drops below freezing for short spells a few times during the winter with a once in 10 years big freeze.  That is all changing though as the climate changes it seems; winters are getting much milder.
In the process of the remodel I need to bring the roof up to current insulation code. Not a lot of room in the rafters for insulation thus I’m planning on exterior insulation to help the cause. I’ve read lots of good discussion here regarding the topic of rigid exterior roof insulation over the years. I have a pretty good idea of what I want to do to achieve this but I just wanted a second opinion on my plan and to check if the thinking and or science has evolved over the last few years.

My plan for the roof is as follows:
*2×6 rafters sheathed with 5/8 CDX (existing) dubbed at the wall plane
*Rafters will be filled with Rockwool batts and covered to the inside with drywall or tongue and groove planks
*Pro Clima Mento 3000 taped and sealed above the roof deck to be integrated w Gutex clad walls for a continuous air barrier
*2″ foil faced polyiso taped
*2″ xps (or polyiso) foamed/taped (xps here has lower r value because of a different blowing agent btw)
*2 layers of 2x strapping vertical and horizontal per roof mfrs. spec
*Ruukki Hygge metal roof

My biggest point of concern is that of an interior air barrier on the ceiling and whether that is necessary or not. From my reading I understand that with this assembly the interior air barrier is to be left off for drying capability. Would that also be true of something moisture variable like Pro Clima Intello?
The other builders who I have spoken to here either swear by a full interior air barrier or totally vapor open with wood fiber insulation and panels like the Gutex or Agepan systems. They see this kind of system I am proposing as a fool’s errand.
Wooden building in the modern sense is relatively new in the Netherlands. It has recently gotten very popular as it is seen as a lower carbon alternative to traditional concrete and brick houses. Vapor open assemblies are ‘the thing’ right now with most wooden builders. Many builders see no other way if you talk with them. People have a long history here with cold and damp brick houses and I think that is a common reference point.
I’m frequently told plywood and osb should never be used on the outside face of the framing because it traps moisture. In my years long experience building and repairing homes in a marine climate in North America I don’t really find this to be true but maybe I’m missing something when it comes to higher performance building? I’m coming from a meat potatoes house building background after all.
I’m just looking for a little feedback…does anyone have any thoughts about this or see trouble with the plan I’ve proposed or have better ideas? Any input anyone has is greatly appreciated.  Thanks in advance!

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  1. Expert Member


    It's important to distinguish between air and vapour barriers, although some materials like poly are both).

    Air barriers are benefit in every roof and wall assembly, and multiple ones are fine.

    Vapour barriers can impede drying to the interior on roofs with exterior insulation, but variable perm ones like Intello work well.

    1. kabouterhout | | #2

      Hi Malcolm -Thanks for getting back to me. Sorry that was a little unclear on my part. I indeed meant vapor barrier when I was talking about the inside of the roof assembly. Gotta get my terminology dialed haha.
      So as I understand it then a variable vapor perm barrier would be ok... I guess to further the question, would it be beneficial in this case or just money and effort for no real gain?

      1. Expert Member
        MALCOLM TAYLOR | | #3


        I don't see much use in including it. I think it will be a well-performing roof without the interior variable perm vapour-retarder.

        1. kabouterhout | | #4

          Sounds good to my ears. Thanks very much for your replies.

          1. Expert Member
            MALCOLM TAYLOR | | #5


            Good luck with your project!

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