Based on our property damage inspections, it appears that the epidemic
of wall rot problems of homes with exterior plaster continues unabated. Perhaps you have heard that some people call
eastern Pennsylvania the stucco failure capital of the US. In some other states, the rate of exterior
plaster wall failures is more than 50 percent!
Now we see significant wall rot in many newly built homes, as well. The key to figuring out the cause and origin
of the damage is to determine where the water is coming from and to determine
the wall component systems.
There
are only two sources of moisture: it either comes from the exterior in the form
of rainfall/leaking air conditioning unit, etc. or it comes from the interior
in the form of water condensation. Of
these sources, by far the most common is rain.
Rain (or melted ice) can enter a wall through many mechanisms: missing
or defective window flashing, missing kick-out flashing, missing or defective
roof flashing, ice dams, splash back, inward solar vapor drive, etc.
Exterior plaster homes includes: cement plaster, hardcoat and EIFS stucco,
adhered masonry veneers (pre-cast stone, natural thin cut stone or thin brick
system veneers). Manufactured
masonry veneer is a version of hardcoat stucco where the top coat is replaced
with an embedded thin masonry veneer (stone or brick). Stucco claddings coupled with manufactured
stone veneers are hugely popular because of their beauty—among other things. Unfortunately, the beauty is often only skin
deep, as they are also commonly linked with moisture problems. This was not always the case and the reasons
for the change in performance are due to several changes in the manufacturing
components and in the construction habits, such as:
·
Changes
in the properties of building papers and water resistant barriers (WRB’s)
·
Change
from plywood sheathings to Oriented Strand Board (OSB) sheathings
·
Higher
levels of thermal resistance
·
Use
of interior plastic vapor barriers
·
Changes
in the properties of stucco renderings
Based on our inspections, the more risky home constructions include the
following components:
·
One layer of felt, building paper, or
house wrap, rather than two layers
·
OSB sheathing which is more susceptible
to rot than plywood or board sheathing
·
Fiberglass insulation
·
Poly vapor barrier that prevented the
walls from drying to the interior
·
Gypsum board
·
Lack of ventilated air gap
·
Flashing missing or improperly
constructed
·
High indoor humidity (such as homes
with humidifier), coupled with an imperfect air barrier
The wall rotting risk could have been reduced by using two layers of
Grade D building paper or equivalent house wrap, and class II vapor retarder
(e.g. Kraft facing). The least risky
construction method consists of installing a drainage gap between the stucco
and sheathing. We also encounter
improper installation of the EIFS or stucco cladding, such as: improper
sloping, lack of backer rod and sealant, improper installation of the foam
insulation, etc. The construction errors
we see on daily basis are sometimes hard to fathom. Incorrect construction appears to have been
prevalent during the go-go days of the last house building boom.
Metropolitan
Engineering, Consulting & Forensics (MECF)
Providing Competent, Expert and Objective Investigative Engineering and
Consulting Services
P.O. Box 520
Tenafly, NJ 07670-0520
Tel.: (973) 897-8162
Fax: (973) 810-0440
E-mail: metroforensics@gmail.com