[Greenbuilding] Exterior insulation retrofit

JOHN SALMEN terrain at shaw.ca
Mon May 23 16:45:08 PDT 2011

All the eifs systems I've seen marketed for Canada that are adhered provide
either a 10mm grooved insulation board (and make a point of advertising the
fact) or use the notched trowel or ribbon method. Trowel or ribbon size is
generally specified as 3/8 to 1/2 and even knocked down the end gap will
still be 6mm or greater. So 'would' or 'should' aside that is pretty well
how eps boards are going up on buildings and how people are being trained
(however sensibly). I'm also seeing mechanically adhered systems over a 10mm
stock drainmat. That is about it for standard practice that I am aware of.

-----Original Message-----
From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of John
Sent: May-23-11 2:52 PM
To: Green Building
Subject: Re: [Greenbuilding] Exterior insulation retrofit

The article says "The flow of air through a 20 mm cavity is not great, but
any airflow reduces the insulating effect of the outer-most layer."
No one would put a 10 mm gap behind the insulation. Or rather, no one
The 10 mm gap is an OK minimum for ventilation, or fine if you want to use
it as capillary break, but systems that drain behind the insulation do not
need or want to be ventilated and use some sort of material to act as the
capillary break.
That 10 mm thing is such a major confusion, I wish they had never put it in

The research we did, together with ORNL, stopped at cavities of 6 mm since
this was thought to be bigger than anything sensible.  Building science
researchers often dont imagine that people might try to do something they
shouldnt (like using a 10 mm cavity behind insulation!). This is the work we
did to show that a 10 mm gap was not needed for drainage: alas, the IRC/NRCC
tested a 10 mm gap (nothing smaller) and that is what got into the code.

On 2011-05-23, at 2:02 PM, JOHN SALMEN wrote:

> Which cavity are we talking about? 
> The NZ requirement I referenced was for any drainage/ventilation cavity -
> don't think a size was specified. Our code requires 10mm which is an
> arbitrary number except that it is a nice round one (and close to 3/8" -
> though it is surprising how picky building inspectors can be on .0187 of
> inch. Our building code requires bottom drainage of a 10mm gap but does
> require top venting. 
> So what I was originally looking for was any research relevant to d-rating
> insulation over a 10mm (or so) drainage gap and it seems there really
> any. 

Dr John Straube, P.Eng.
Associate Professor
University of Waterloo
Dept of Civil Eng. & School of Architecture

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