Thermal and Moisture Control in Exterior Metal Walls

Achieving durable, economical, and sustainable metal wall systems
This course is no longer active
[ Page 2 of 12 ]  previous page Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 next page
Advertorial course provided by CENTRIA
Peter J. Arsenault, AIA, NCARB, LEED-AP

2. Performance Requirements for Outer Wall Materials

The weathering element of a multi-component wall system is the outer wall material. In addition to being the aesthetic wrap for the building, it is very important in determining the rest of the wall system design. Moisture management begins with the selection of this outer material.

Porous Materials
Materials like masonry, precast concrete, Exterior Insulation Finish Systems (EIFS),and Glass Fiber Reinforced Concrete (GFRC) are porous materials that will absorb and retain moisture. Wind-driven rain in particular can be an issue for these porous building materials that challenge designers to address the conditions that arise after a storm. When the sun heats up the outer wall, the absorbed moisture is changed to water vapor. The vapors move from the warm, high-RH area to the colder, often air-conditioned interior. A problem can occur in cold or moderate climates where the vapors can pass through the wall system components, enter the wall cavity, and condense.


Figure 1
Wet porous materials are prone to moisture in wall cavities when heated by the sun

Non-Porous Materials
Other materials, like metal, glass, and polymer-based walls are non-porous and do not retain moisture. They eliminate a large portion of the moisture or water vapor problem through their characteristic of not absorbing water. Metal cladding systems are such materials and they can further be designed to act as rainscreens, to minimize water entry and to ventilate wall cavities where moisture can collect.

3. Climatic Zone Considerations

Each of the four U.S. climatic zones raise varying degrees of moisture concerns. (Figure 2) In the southeast, during the summer months, the hot and humid ambient conditions can lead to entrapment problems in the wall system. For the northern states, moisture control is more moderate during the summer, while controlling moisture from interior conditions during the winter is critical. Arid areas are considered low risk and do not have moisture problems.


Figure 2
U.S. climatic zones map

 

[ Page 2 of 12 ]  previous page Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 next page
Originally published in Architectural Record.
Originally published in January 2006

Notice

Academies