[Greenbuilding] Exterior insulation retrofit

John Straube jfstraube at gmail.com
Wed May 18 07:24:12 PDT 2011


The class action suits Eli mentions where in the early 90s were not drained, relied on caulking to keep water out.  Not surprisingly, caulking failed, windows leaked, and disaster ensued.  Drained systems have not had these problems.
The question: "does a drained gap behind the insulation short-circuit insulation" has not been definitively answered. It has been studied and reported on however.
What is clear is that a small gap (say 1/16" or less) with a drain opening at the bottom only works very well as a drainage system and has a small impact on R-value.  How small? Hard to tell, but under 10%, and my best estimate is 3-5%.
If you have larger gaps and vent openings top and bottom, then the loss will be greater and can be rather significant in theory.
So, use a small gap and vent only.
Also, if you dont like EPS foam (Rob Tom?) you can install EIFS over high density Rockwool.  We tested such a system in the mid 90's, which had large vent openings (trying to get pressure equalization, which was the fad then), and could not see any impact on R-value, but it was a field test so we cold not really measure better than 10%.

The drainage plane on the substrate should be high quality: building paper does not cut.  EIFS producers sell fluid applied air and water barriers that are high performance.

The most problematic EIFS are those that use mechanical fasteners (screws) through housewraps.  While they can work, the screws tend to move and cause cracking far too often, and the differential moisture absorption around the screw causes slight discoloration.  After brief flirtatons with mechanically fastened EIFS, most suppliers have gone back to the tried and true adhesively attached version.  While many on this list would prefer not to rely on adhesion (I am one of them) there is a very long track record of success with EIFS, and there are enough problems with screw attachments to make me avoid them.



For stucco (cement, sand mixes) cladding over insulation, different rules apply.


On 2011-05-18, at 9:58 AM, elitalking wrote:

> Exterior Finish Insulation System does provide the exterior finish, thereby reducing the cost of another finish. I know dryvit had a class action lawsuit that was settled for bulk water drainage problems.  Ultimately the solution was to assume imperfections in the flashing installation and manage the water by overlaying a building wrap on original wall with a drainage space maintained.  My question is does that drainage space on the conditioned side of the insulation create a convective path for air leakage? In the best of all worlds, the building wrap would be a perfect air barrier. Just as with the bulk water flashing, perfection is hard to achieve.  Could that be a source of air leakage from the building?
> 
> In my installation, I located the bulk water drainage outside the insulation with 3/4" osb furring strips for siding screws.  I attempted to seal between the insulation boards to achieve tight air barrier.  I also added a redundant building wrap layer to do the same.  Both were vulnerable to imperfections.  However, there is no known hole on conditioned side.
> 
> Eli
> ----- Original Message ----- From: "John Straube" <jfstraube at gmail.com>
> To: "Green Building" <greenbuilding at lists.bioenergylists.org>
> Sent: Tuesday, May 17, 2011 9:42 AM
> Subject: Re: [Greenbuilding] Exterior insulation retrofit
> 
> 
>> Being done all the time in North America.  Although this really only got common in the last decade.  I expect to see a lot more.
>> The problem is, you have to like the look of stucco, which is not always what is wanted, and the impact resistance of EIFS leaves lots to be desired.
>> 
>> On 2011-05-17, at 9:27 AM, Norman Feldman wrote:
>> 
>>> In April I heard an architect describe how they're using EIFS insulation in Germany and Austria to insulate existing buildings from the exterior. They apply EIFS panels to the outside of the building while tenants are in the building then, once the insulation is done, bring the windows out. I will forward more about this offlist if anyone wants.
>>> 
>>> http://en.wikipedia.org/wiki/Exterior_Insulation_Finishing_System
>>> 
>>> 
>> 
>> 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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