MDC® has modeled and analyzed the following building system conditions using both traditional ASHRAE wall section analysis and WUFI® advanced modeling techniques.

Traditional Design – New Materials; New Opportunities For Failure
While basic building designs have remained relatively constant over time the introduction of new materials into the traditional building envelope designs has created new moisture penetration and retention problems leading to failures. Water in its various physical states can cause major problems when it appears and remains within building systems. While some materials of construction and assembly systems can tolerate moisture penetration and elevated levels of water for short periods of time without damage, others are easily susceptible to damage over both short and longer timeframes. MDC has utilized both traditional and advanced analysis techniques to investigate, analyze and correct moisture penetration problems in the following situations.

• Pharmaceutical Plant – Humidity Control Problems
• Airport Terminal – HVAC & Moisture Analysis
• Food Processing Plant – Humidity Control Problems
• Electronic Manufacturing Facility Moisture & Humidity Issues
• Commercial Structure – Roof Thermal and Moisture Analysis
• Hospital – Wall Failures
• Townhouses – Window Defects & Moisture Penetration
• Seafront Condominiums – Window and Door Leaks, Moisture Penetration
• Carriage Homes – Stucco Failures
• Single Family Homes – EIFS Failures
• Pennsylvania Stone Farm House – Moisture Penetration

WUFI® Advanced Modeling Techniques
WUFI® analysis uses actual hourly weather data, building orientation and solar data to create boundary conditions that are realistic of the actual exposure conditions. A WUFI® simulation considers the simultaneous effects of both heat and moisture on the building envelope. Rain and solar radiation are considered on exterior surfaces. Individual hygrothermal properties of each material in the building system are accounted for in each layer of the building section, including properties such as thermal conductivity that vary according to the humidity level in some materials. The resulting data are then displayed in graphical form and provide a time related history of the seasonal variations of the conditions within the building envelope system. WUFI® results have been validated by actual laboratory tests and outdoor weathering tests..

As mentioned above WUFI® data output produces meaningful graphical time related graphs which can be utilized to explain the hygrothermal phenomena that are occurring in the building system envelope. An example is shown below of a typical home construction wall using 2 inch x6 inch wood framing members with stucco exterior finish located in the Philadelphia weather area.

Latent Defects Leading to Failure in Structures using EIFS
Numerous reports of accelerated failures in institutional, commercial and residential buildings exterior wall systems attributed to water accumulation in the exterior wall cavities are raising concerns about structural soundness at many properties. MDC® has investigated and analyzed numerous failure situations and has reached the following general conclusions concerning the cause of the failures in these artificial.

Stucco Systems:

• Unsuitable materials are used for the application.
• Construction design details are often ignored in light residential construction.
• Flashing is not properly sealed.
• Penetrations are not properly sealed.
• Materials are not applied within the temperature and humidity limits specified
• Window and door openings are not properly flashed, sealed, and caulked.
• Other unique design and construction factors result in accelerated failure.
• Moisture is “trapped” within the wall cavity
• Mold Growth and indoor air quality problems can also occur as a result of water intrusion.

Based upon our recent experience, MDC® has determined that there are four primary mechanisms which result in water damage on a typical residential or commercial structures that incorporate EIFS.

• Exterior Joint Penetrations
• Air Pressure Differentials
• Entrapment of Internally Generated Water Vapor within structure
• Entrapment of exterior source water within the structure
• Material Permeability

Some or all of these mechanisms are at work in failure situations and depending in the severity of the condition, the apparent deterioration can be delayed or accelerated. MDC® has modeled and analyzed these conditions using ASHRAE wall section analysis and WUFI®. As noted above WUFI® is a proprietary computer program which allows realistic calculation of the transit couples of temperature and moisture levels for one- and two dimensional heat and moisture transport in multi-layer building components exposed to natural weather. As temperature and humidity change, the exterior surface of a structure continuously contract and expands. Differential expansion occurs whenever dissimilar materials are in direct contact eventually leading to moisture intrusion. A wood door frame, a window, a metal penetration or EIFS base coat all expand and contract at different rates.

Traditional Cement Stucco
As discussed above the introduction of new materials and the changing nature of the components of the stucco itself can lead to moisture penetration issues. Stucco mixes utilizing lime are to a large degree “self-healing” when surface cracks develop over time due to the normal settlement and movement in structures. However the movement away from lime additives has resulted in open cracks in the stucco surfaces that do not “heal” with time. Differential pressure on the structure caused by HVAC system operation or wind effects draw significant amounts of water through open cracks and this water can become trapped inside the wall cavity leading to moisture related failures.

The use of felt paper ( Tar Paper ) under the exterior wall surface has been a standard element of traditional building construction. Substitutions of other materials for the felt paper and/or the elimination of the “Tar” from the paper has also contributed to the moisture penetration issues and left the wall section vulnerable to damage from the moisture penetration.

As discussed above for the EIFS failure mechanisms these same weather related conditions coupled with wind pressure differentials and internally generated moisture conditions often combine in ways that lead to failure conditions.

Precast Concrete Wall Systems
Recent MDC experience with precast concrete wall systems has shown that they are also vulnerable to moisture penetration problems. In one unique situation interior humidity conditions combined with exterior weather events and conditions resulted in significant moisture problems internal to the building and within the wall section.

Sample WUFI Analysis