OM-01-16
Design Note
Vapor Retarder
Recommendations
In some buildings water vapor protection is absolutely
necessary. Fortunately, these are also applications
where the vapor drive is consistently from one side of
the wall to the other, making it less likely that a vapor
retarder would ever act as a condensation plane; for
example.
1.
2.
3.
extremely cold climates
extended high humidity levels
special applications such as coolers or
freezers
Low density Icynene® is not a Type II vapor retarder,
however, it can be used as the primary resistance to
airborne moisture transport in mixed heating/cooling
and cooling climates. The air seal capability of
Icynene® limits air leakage and controls convective
moisture flow which can be the major moisture
transfer mechanism through the building envelope. In
many applications, where the vapor retarders would
limit drying, Low Density Icynene® provides the
opportunity to eliminate vapor retarders from the
assembly and thereby improve the drying capability of
the building envelope. In other applications, where
vapor protection is required, the standard
polyethylene vapor retarder can be replaced through
the use of vapor retarder paint.
Beyond vapor protection there are also other design
considerations as well with vapor retarders. Certain
vapor retarders can impede the drainage from and
drying of the assembly in the event of roof and pipe
leaks. This may make such problems more difficult to
diagnose and correct. The vapor protection should
therefore be selected so as not to impede the drainage
of liquid water in the event of this type of water
intrusion. Vapor retarder paint, as opposed to
polyethylene has been found to be an innovative
solution that saves costs and provides for drainage
through light density foam in the event of a leak. This
paint can be applied directly to the insulation, prior to
the installation of gypsum drywall or alternately it can
be directly on the drywall as a primer (thus not
requiring extra labor). Icynene has tested several
products applied directly over LD-C-50® which
qualify as a Type II vapor retarder. Consult your sales
representative for the most up-to-date list.
In areas where no vapor protection is required on the
interior, a more permeable paint primer can be used.
The elimination of the vapor retarder in air
conditioned buildings allows for drying to the interior
during the cooling season. With the removal of the
vapor retarder, moisture can diffuse through the
interior finish materials into the interior air space
where it can be taken out of the air by the air
conditioning system. The benefit of vapor retarder
removal has been recognized in the 2009 IRC which
now allows for vapor retarders to be optional in
Climate Zones 1 through 4. It is also not required in
Zones 5 and above if enough continuous insulation
exists on the exterior of the wall such that interstitial
condensation is not a risk.
Vapor Retarder Classifications
Vapor retarders that are classified as Type I (0– 0.1
Perms) and Type II (0.1–1.0 Perms) are required on the
interior side of frame walls in climate zones 5, 6, 7, 8
and Marine 4. The codes allow for vapor retarders to
be optional in climate zones 1 through 4.
Medium Density Spray Foam
Icynene medium density spray foam insulation
materials such as MD-C-200™ are a Type II vapor
retarder with a perm rating less than 1.0 at a 1.5” or
greater thickness. In zone 5 and higher or Marine 4, a
medium density spray foam application with a perm
rating less than 1 can provide the requirement for a
Type II vapor retarder. A layer of medium density
foam on the towards the outer side of the cavity can
also be used to warm the wall cavity so condensation
will not occur. The IRC provides details as to how
much thermal resistance is required but generally at
least 1.5” of medium density spray foam will be
required.
Interior Relative Humidity
In Climate Zones 4 and 5, the reversal of vapor drives
between the summer and winter seasons is best served
by assemblies that are breathable (vapor permeable)
and allow for drying to the interior in the summer and
the exterior during the winter. The prevalence of air
OM-01-16
conditioned buildings makes it even more important
to be able to eliminate vapor retardant materials in
assemblies. In these climate zones, the need for vapor
protection can be made unnecessary by controlling
interior relative humidity levels.
In terms of building durability, maintaining
humidities lower than 35% RH is preferred, but low
humidity levels are generally not comfortable to
occupants. For example, very low humidity is
associated with increased static electricity, nose bleeds,
and skin irritation. Maintaining interior humidity
levels at around 35% RH provides both comfort and a
reasonable assurance of building durability.
Increasingly designers are opting to control humidity
through the installation and use of a mechanical
ventilation system. All houses insulated and air-sealed
with Icynene® should have a mechanical ventilation system
to supply fresh air. The building code sets a minimum
standard for supplying fresh air to a building, and, in
an airtight house, such as a home fully insulated and
air sealed with Icynene products, this can only be
supplied through mechanical ventilation.
Elevated Interior Humidity
There are many applications where the demands of
the design create interior humidity levels above 35%
RH. This can include areas around swimming pools,
saunas, greenhouses, showers, etc. For most of the
year the indoor humidity levels will be higher than
those outdoors, and moisture drive will be
consistently from the interior of the building into the
insulation. In these cases, a vapor retarder should not
be removed from the assembly, and should be
installed on the interior face of the insulation.
Coolers & Freezers
Like indoor pools, coolers and freezers present a
special situation whereby moisture is always traveling
in one direction. However, unlike pool rooms,
moisture is typically traveling into a cooler or freezer
from the outside. This situation presents both special
advantages, and special design considerations.
One of the special advantages with these specialized
structures arises from the fact that many coolers/
freezers are entirely located within a conditioned
building. As well, moisture that enters the freezer is
often managed by the mechanical system that handles
Design Note
cooling. In this situation, it is important to ensure that
no major obstructions to moisture flow exist on the
interior finish of the cooler. If the cooler is insulated
from the inside, moisture that penetrates the Icynene
is conveyed into the cooler/freezer, where it is
removed from the interior air by the cooling system.
Many coolers are framed with cold-formed steel
cladding on the interior. If the Icynene is installed by
spraying the outer face of the steel cladding, the
cladding acts as a cold-side vapor barrier. Medium
density spray foam is usually specified to limit
moisture diffusion through the assembly.
Where any wall of the cooler is also an exterior wall,
the wall can be exposed to reversals in vapor drive. In
this case, the inclusion of a vapor retarder and its
location is at the discretion of the designer, depending
on local climate.
Icynene ®
All Icynene® spray foams are also air barrier materials
that will prevent the flow of air leakage driven
moisture into the building envelope. With Icynene®
there is no need for a sealed poly vapor retarder to act
as an air barrier to prevent convective moisture flow
into the building envelope. As a result, the installation
of the polyethylene is greatly simplified.
No
additional sealing of polyethylene joints is required
By preventing air leakage, both Low and Medium
Density Icynene® spray foam is able to eliminate the
need for a vapor retarder in many climate zones and
living conditions. If the need for a vapor retarder is
eliminated, the drying ability of building envelope
assemblies is maintained, thereby improving the
overall quality and durability of the structure.
Nevertheless, vapor retarders remain a necessary part
of many projects. In many cases, the use of vapor
retarder paint provides an innovative way of getting
the benefit of vapor protection without compromising
drainage through the assembly. In some applications,
however, like freezers and coolers it may be necessary
to pay the premium for Medium Density Icynene
spray foam to get the needed protection from
concealed condensation.
HEALTH & SAFETY
HOMEOWNERS
COMMITTED TO THE RESPONSIBLE USE OF SPRAY FOAM
CHEMISTRY FOR OVER 25 YEARS.
Icynene products have an excellent health and safety record spanning more than
350,000 insulation projects over more than 25 years. Nonetheless, safe handling
practices during and immediately following installation are required to eliminate
the possibility of health effects from exposure to isocyanates. Asthma, other
lung problems, and irritation of the nose and throat can result from inhalation of
isocyanates. Direct contact with the skin and eyes can result in irritation. Different
individuals will react differently to the same exposures; some will be more sensitive
than others.
Everyone (other than Icynene-certified spray technicians) must vacate the job site,
remaining completely out of the building or at least 50 feet away, while the spray is
applied and for at least 24 hours after spraying is completed to allow active ventilation
of the job site and to ensure the foam chemicals are completely cured. No exceptions.
Independent studies indicate that with 24 hours’ active ventilation after spraying is
completed, Icynene spray foam insulation is safely cured.
WARNING
STAY OUT OF PREMISES
WHILE FOAM IS
SPRAYED AND FOR
24 HOURS AFTER
SPRAYING IS COMPLETE
THE EVOLUTION OF INSULATION™
SL-506-02 Updated March 2013
ICYNENE Inc.
•
6747 Campobello Road, Mississauga ON L5N 2L7 Canada
•
ICYNENE.COM