[Greenbuilding] exulation

[JOHN SALMEN]

There are a couple of basic considerations that to be kept in mind. 

-          Adding the insulation to the exterior increases the temperature
of the sheathing so technically reduces the risk of condensation depending
on weather (and interior air leakage which is the big concern)

-          Adding insulation reduces the ability for a wall to dry to the
exterior so the wall needs to have the ability to dry to the interior
(existing vb may be a problem)

-          Any potential for condensation in our climate is primarily a
result of interior air leakage during heating season so an interior air
barrier is crucial (caulk sealing, electrical gaskets, etc.)

 

I prefer eps boards which you can get in full 4'x8' - type 1 is about 4 per
inch and type 2 a little higher (4.5?)

 

From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Chris
Koehn
Sent: March 21, 2011 11:55 AM
To: greenbuilding at lists.bioenergylists.org
Subject: [Greenbuilding] exulation

 

I am planning some work on a 1970's single storey home here on Vancouver
Island. Replacing windows is the impetus. The home has vertical cedar
channel siding over tar paper over sheathing (both ply and solid sawn
recycled form wood in different areas) over 2X4 framing with fiberglass batt
insulation, over 6 mil poly vapor barrier over GWB. We are in zone 4C,
"mixed marine" with roughly 5400 f HDD. Our heating season is long but
rarely severe.
<http://www.greenbuildingadvisor.com/sites/default/files/H-T%20Zones%20-%20l
egend.jpg>

 

I'm considering removing exterior siding and adding a layer of rigid
insulation while I'm at it. Some siding needs to be removed anyway for
window replacement and some in other areas needs to be replaced due to
flicker damage, so taking it all off (and re-using it) doesn't seem to me to
be a substantial added burden. 

 

Quoting the U.S. DOE site: "Foam board insulation is commonly placed between
the exterior finish (i.e., siding, brick) and the studs of exterior walls.
To prevent air infiltration, you should place rigid insulation boards
tightly together and seal the seams with tape or caulk. However, this
practice may worry some builders in cold climates since the foam board may
act as a second vapor diffusion retarder. Studies have shown, however, that
condensation rarely occurs in these areas unless something else is seriously
wrong with the wall assembly (i.e., massive uncontrolled air leakage into
the walls from the house). If the assembly is constructed correctly, the
inside surface of the foam board stays warm enough to keep water vapor in
its gaseous state long enough for it to escape."

 

In the few areas I have opened the walls up I have seen no evidence of
condensation, though in some areas near the top plate some of the insulation
has turned grey, indicating air moving through it. It is possible, I
suppose, the air that's moving through the wall is not coming from the
inside.

 

My questions to the group are:

* Given our climate and wall profile, is adding insulation to the outside a
good idea?  

* Is there a type of insulation recommended for this work, specifically in
light of any concerns over moisture drive, as well as a desire by the client
to keep the thickness build-up minimal, and of course cost.

* What are suggestions around detailing: joints between insulation panels,
treatments at the bottom (siding currently laps directly over brick, which
is applied to a concrete foundation), fastening schedules (insulation and
siding), drainage plane. The house has min. 2' overhangs. 

 

Thanks as always,

 

Chris Koehn

TimberGuides

Cobble Hill, BC

 

 

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