Metropolitan Engineering Consulting and Forensics

CAUSE AND ORIGIN INVESTIGATIONS: ROTTED WALLS IN EXTERIOR PLASTER HOMES

CAUSE AND ORIGIN INVESTIGATIONS: ROTTED WALLS IN EXTERIOR PLASTER HOMES

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

Web pages: https://sites.google.com/site/metropolitanenvironmental/

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