[Greenbuilding] Exterior insulation retrofit

Fri May 20 20:03:07 CDT 2011

I'm a bit stuck on this one. Not fastening mechanically means relying on a
liquid applied wrb typically on a gypsum board - which is the recommended
substrate. Now as in the past that will work great for 95% of the surface
but any seam larger than 1/4" will be a problem (as per 'high performance'
barrier suppliers spec). I've rarely seen any kind of sheathing applied that
does not have larger gaps somewhere and have also seen sheathing buckle as a
result of no gaps. Also 2x framed buildings move, foundation settle, etc... 

In my thinking any sheathing with a liquid membrane will not be complete and
will typically fail along an otherwise impermeable drainage path (isn't that
how things work) largish cracks in an impermeable path allow large flows
which prevents any potential for drying in that path (despite the gap) which
results in some spot of saturated wood/gypsum that has limited drying
potential and becomes food for decay.

Mechanical fastening perforates the wrb thru the drainplane with probably a
couple of holes per sq.ft. which could also lead to problems but I can't
help but think that most flows in this situation would be directed as
drainage against a layered wrb and any moisture thru a screw hole has
greater potential for drying in the assembly.

I am saying this as I am considering using a liquid wrb on a ply sheathed
building and my common sense tells me that it is the wrong approach - I am
embarrassed to say that my concern is the aesthetic telegraphing of the
screws (which is all anyone sees) as well as being in compliance with some
local practice.

By the way I think NZ has quantified the insulation loss for air movement
with drainplane for eifs at something around 20% (if memory serves) as a
code modification for insul. Values. I need to check that memory.

John

-----Original Message-----
From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of John
Straube
Sent: May-18-11 7:24 AM
To: Green Building
Subject: Re: [Greenbuilding] Exterior insulation retrofit

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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> 
> 
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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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