[Greenbuilding] Exterior insulation retrofit

John Straube jfstraube at gmail.com
Mon May 23 17:08:30 PDT 2011


10 mm grooves is not the same as 10 m continuous.  A rough approximation of the equivalency is the area of the gap. So a 10 x 10 gap every 100 mm would be equal to 1 mm. In reality, the flow is lower than this.
We measured Dryvit and Sto ribbon systems and did not find gaps of over 3 mm.  And when tested for airflow, they were much smaller. Equivalent to 1-2 mm.  See attached graph. Wall 1 is the standard dryvit, Wall 4 is grooved insulation. Test was pressure vs flow and then correlated to equivalent wide gap.
So the two market leaders are testing and and certifying systems of this type.  Could be you are seeing something else, but I deal directly with the people who are in charge of technical development for these systems and they dont think they are installing larger gaps.

The drainmat solution I am aware of and this is a bit of problem. This was all driven by the 10 mm drained and ventilated gap developed for siding and stucco.

In short, I would not use insulation over large gaps, like 6 or 10 mm, and sure would not try to figure out the derating: they would depend too much on wind gusts, exposure etc.
If the wind hits the building just so, a gap of 10 mm vented top and bottom can result in massive flow, with derating of insulation of something like 90%.  Research results are clear for these types of systems.
It is for the drained systems with small gaps that the question remains, is the derate 3% or 10%.


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On 2011-05-23, at 7:45 PM, JOHN SALMEN wrote:

> 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
> Straube
> 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
> should.
> 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
> there.
> 
> 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 -
> I
>> 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
> an
>> inch. Our building code requires bottom drainage of a 10mm gap but does
> not
>> 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
> isn't
>> any. 
>> 
> 
> Dr John Straube, P.Eng.
> Associate Professor
> University of Waterloo
> Dept of Civil Eng. & School of Architecture
> www.buildingscience.com
> 
> 
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Dr John Straube, P.Eng.
Associate Professor
University of Waterloo
Dept of Civil Eng. & School of Architecture
www.buildingscience.com



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