Spray Foam in the Building Envelope*

The building envelope is a total system of construction
materials and design components that control the
temperature, movement of air, and moisture both into and
out of the building.  A building's insulation, air barrier and
vapor barrier all need to work together.  Doing so achieves
a more stable, comfortable and healthier indoor
environment.  Many new materials and design practices
are being implemented to extend the sustainable service
life of buildings and homes.




Build it Tight, Ventilate Right.*

Ventilating the Attic and the Crawl Spaces has long been
the traditional and code required method of home design
and building.  However, ventilation of these spaces was
required because standard materials and building design
practices were not capable of addressing radiant heat
transfer and condensation.
In order to address heat transfer from weather issues,
utilities, and the formation of moisture due to
condensation and air infiltration, the only option was to
ventilate the attics and crawl spaces.  The major problem
with ventilating these spaces is that the air brings
moisture, pollution and other adverse problems and
challenges with it.  Furthermore, the vents create voids in
the building for insects and rodents to enter.  These vents
will also create a negative pressure in the attic, or suction,
that will pull conditioned air from the house, into the attic
and blow it right outside.  Conditioned air costs you
money!  Why would you want to throw it out the window?
In fact, in the summer, the incoming air needs power
consuming fans to bring it in, and it will never get any
cooler than the outside air temperature.  Why would we
want 95 degree hot, humid, potentially pollution ridden air
into our attic and crawl space?  In the winter this air is
freezing cold.  
If our heating/cooling utilities and ducts are located in the
attic and/or crawl spaces (most usually are) then their
radiant contact with the ducts will cause them to loose up
to 10% or more of the hot or cold air flowing through them
due to radiant transfer.  Worse yet, moisture and mold can
also form within the ducts during certain temperature
conditions, causing adverse health affects to the building
occupants, or your family.
Another major reason that traditional methods call for attic
ventilation is that during the hot summer months, heat
from the sun builds on the roof and radiates into the attic
space.  In fact, it can build to upwards of 130 to 150
degrees or more.  This extreme heat radiates into the attic
and living space causing condensation and the potential
for mold.  Our air conditioning systems also need to work
harder and consume more energy with all this heat directly
above our heads.  The extreme heat also makes it very
uncomfortable to enter these spaces.  
Most builders and design professionals are not familiar
with modern materials and progressive building science
techniques that can virtually eliminate all of these
problems that force the traditional, less effective
requirement for ventilation in these building spaces.  
Builders and design professionals will also make the
argument that your home needs to breathe.  Well, they are
absolutely correct.  But why rely on cracks, gaps and
holes in your building for passive ventilation, when you
can build your home tight, healthy and energy efficient,
and let the mechanical ventilation systems due the job
properly.
Spray foam insulation can still provide benefits far greater
than traditional materials such as fiberglass and cellulose,
regardless of whether you decide to ventilate these spaces
or not.  By using spray polyurethane foam insulation you
can increase your home's energy performance, structural
integrity and air quality.

*Courtesy of www.sprayfoam.com.    
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