When “Going Green” Goes Bad
WHEN THE HOLLMANNS BEGAN
building their luxury family home among
the other million-dollar estates dotting
prestigious Miramar Lane, deciding to
use an environmentally friendly insulation material seemed like a great way
to “go green.” Little did they know that
within the span of a few years this decision would land them in court, battling
over a property now worth less than
their neighbors’ garages.
At the center of the controversy is a
two-story, 9,000-square-foot residence
located in what the U.S. Department of
Energy rates as a “hot-humid” climate.
The exterior featured a lovely natural
stone veneer; the interior boasted expensive hardwood paneling. But when
the Hollmanns started discovering fungal growth on the walls, they quickly
learned the water intrusion was not
stemming from the usual suspects—
the building envelope components of
exterior walls, roofing, or doors. Rather,
it came from within.
Anatomy Of An Envelope
A building envelope is the assembly
of materials that separate the exterior
environment from the interior of a structure. The envelope serves as the outer
shell or the “skin” that protects the
building from the elements and facilitates climate control within the same.
Water will enter your home; building envelope components are designed and
constructed to shed or drain that water
to the exterior and away from the skin of
In residential construction like the
Hollmanns’, a masonry veneer cavity
wall system typically consists of the following components, listed in order from
exterior to interior: brick or natural stone
masonry veneer, air space, weather barrier and/or vapor retarder, load-bearing
wall, and interior wall finish. Thermal insulation is used within the wood-framed
Thermal insulation is installed inside
the exterior stud wall to slow the rate
of heat transfer across the exterior wall.
Common types of insulation in residential construction include fiberglass batt
insulation and cellulose insulation.
Cellulose insulation is made from recycled paper and treated with mold retardants and fireproofing chemicals. It
is installed using either dry or wet-spray
techniques, with wet-spray being the most
common application in residential construction. Like fiberglass batt, cellulose
insulation is also low cost, with a fairly
high R-value. However, cellulose insulation is “hygroscopic,” meaning that it absorbs and retains moisture. As a result,
wet-spray cellulose insulation in particular
has two important application limitations:
1. It requires an experienced installer.
2. It must be allowed to dry properly before it is covered up.
According to the North American Insulation Manufacturers Association (
NAI-MA), studies performed under various
humidity conditions indicate the short-est dry time for wet cellulose insulation
was one month in a dry climate without a vapor retarder in the assembly.
Although the exact drying time allowed
for the Hollmanns’ home is unclear, it
definitely was not a year.
Room to Breathe
Making matters worse, the home-
builder did a great job in sealing up the
luxury residence—perhaps too great.
As stated earlier, water will enter your
home. Architects and engineers accept
this and design for it. Masonry veneer,
like the natural stone used in the Holl-
manns’ residence, is considered porous
or absorptive, and both liquid water and
water vapor will penetrate the masonry
into the air space. The masonry cavity
wall assembly, therefore, must be de-
signed and constructed to drain this
moisture and prevent it from migrating
past the air space and into the stud wall
where it can damage the insulation and
Exterior walls should be limited to a
single vapor retarder to allow a path for
moisture that enters the cavity to escape. If vapor retarders are installed on
both sides of the wall, moisture can be
trapped in the wall insulation and prevent the wall cavity from drying. Further,
some commonly used materials will
function as vapor retarders when they
are not intended to, such as enamel
paints and hardwood paneling.
Peeling Back the Layers
When Nelson Forensics was engaged
to determine the cause and origin of the
fungal growth found by the Hollmanns, a
variety of tests were performed, beginning with high moisture readings at all
the interior finishes at the exterior walls,
and leading to water spray testing at the
exterior, and the eventual removal of exterior stone to inspect the wall cavity.
Excavation revealed that the air space
was filled with mortar and the mortar
was packed against the Tyvek weather
barrier. The Tyvek weather barrier was
then cut to observe the OSB sheathing,
also saturated with water.
When specifying material components, the project designer or builder
must consider the materials’ tolerance
for common construction defects or imperfections, and the following should be
1. Masonry cavity wall moisture intrusion is inevitable and drainage of the
cavity wall is an intrinsic design requirement. It is imperative that cavi-ties are kept clean of mortar droppings during construction.
2. Installation of cellulose insulation
between two materials that perform
as vapor retarders in an exterior wall
is not recommended.
Nelson Forensics continued on p. 52