Building Enclosure Design

Precast concrete provides an efficient, versatile and resilient building enclosure system. Precast wall systems are barrier, or face-sealed, systems. Unlike rainscreen systems, precast concrete does not require a cavity where moisture collects and other problems can occur. 
Thermal Performance 
Due to its density, concrete has the capacity to absorb and store large quantities of heat because its thermal mass allows concrete to react very slowly to changes in outside temperature. This characteristic of thermal mass reduces peak heating and cooling loads and delays the time at which these peak loads occur by several hours.

Energy saving benefits of thermal mass are most pronounced when the outside temperature fluctuates above and below the balance temperature of the building, causing a reversal of heat flow within the wall. The balance point is generally between 50 and 70ºF, depending on the internal gains due to people, equipment and solar effects. These ideal conditions for thermal mass exist on a daily basis at all locations in the United States and Canada during at least some months of the year.

Thermal mass is most effective in conserving energy in the sun-belt regions in the Southern and Western United States  because these daily temperature fluctuations occur throughout the year. Thermal mass also works well when daily temperatures have large variations between the daytime high and nighttime low and when outdoor air can be used for nighttime ventilation. These conditions are most prevalent in the western states. Designs employing thermal mass for energy conservation should be given a high priority in these areas.

The following link provides insights into the determining of thermal resistance (R-value).
R-Value, calculating R-Value, continuous insulation, and thermal bridging

Air and Moisture Management 
Air barriers and vapor retarders are needed in a properly designed building envelope. In many instances, a single material can be used to provide both of these as well as other functions. The principal function of the air barrier is to stop the outside air from entering the building and inside air from exfiltrating through the building envelope to the outside. This applies whether the air is humid or dry, since air leakage can result in problems other than the deposition of moisture in cavities.

Air barriers (sometimes called air retarders) will reduce infiltration and exfiltration. They reduce the potential for moisture problems due to moist air migrating into a building. This moisture can be warm humid air from outside during the summer or warm conditioned air from inside in the winter.

Materials such as precast concrete panels, polyethylene, gypsum board, metal sheeting or glass qualify as air barriers since they are low air-permeable materials when joints are properly sealed.

Click the links below to better understand and design High Performance Precast Concrete building enclosure systems.

Please contact John Dobbs, Executive Director, at jdobbs@pcims.org for more information about High Performance Precast Concrete Building Enclosure Systems. 

Best regards,
John
Contact:
John E. Dobbs, P.E., S.E.
Executive Director

PCI Mountain States Region
10500 Spring Green Dr., Unit 112
Englewood, CO  80112