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School districts are asking much more from new school buildings than ever before. Building codes are also requiring better performance with respect to energy efficiency and life safety. The natural response to these new criteria has been to modify the traditional building system in order to provide the additional performance required. The architecture-engineering-construction industry has found it easier to simply stick with what they have always done and attempt to make modifications to meet the new, highly evolved performance goals.
For wall systems in particular, this has meant adding multiple layers of materials to meet each of the individual objectives. The two most common wall systems used in the construction of school buildings have been concrete masonry and structural steel with light-gauge framing. The challenge for these systems has been addressing the insulation and air tightness required to meet the new energy efficiency goals, while also avoiding fire and life-safety concerns introduced by the additional insulating and air barrier materials.
Adding layers to either of these traditional systems has introduced more complexity in designing the details of a wall system, especially at window and door openings, connections to other building elements, and integration with exterior finishes. These more complex designs have also increased the amount of time and money it takes to construct a school building.
More layers of material means more trades on a job site, more coordination issues as each trade attempts to accomplish their scope of work, and more labor required overall to get the job done. Adding layers of materials to increase energy efficiency results in challenging many contractors’ budgets and schedules.
The hierarchy of needs has focused the attention of design and construction professionals on meeting changing building codes first. Wall component manufacturers have responded by providing code-compliant accessory materials that can be added to masonry and steel frame wall construction. However, many of the options stop at minimum code compliance with respect to energy efficiency and air tightness, and do not significantly improve the performance of the building from the perspective of fire safety, storm safety and long-term sustainability.
Architects, engineers and construction companies need to consider the following when evaluating modifications to existing wall systems like concrete masonry and steel construction for school building projects.
Both concrete masonry and structural steel with light-gauge framing require additional insulation and air barrier layers, and in some cases, multiple insulating materials in an assembly. While these traditional systems have been relatively cost effective to date, the increased number of materials and trades involved in providing a complete wall system today has made construction slower, more complex and more costly. Speed of construction and increased labor costs are significant challenges for these wall systems.
Both systems can be designed to meet the current energy codes, but are expensive in regard to achieving higher performance than code requires. Cost of maintenance and repair for concrete masonry is good, however lightweight steel framing and cavity wall designs are still challenged in the long term with mold, rot and overall durability issues.
Again, with proper air barrier and sealant design and construction, either system can provide a reasonable level of air tightness to reduce the infiltration of allergens and pollutants into classrooms. However, cavity wall construction is much more susceptible to mold and rot which can be compounded by more airtight buildings. For both systems, fire ignition barriers must be installed over the insulation if it’s combustible. Concrete masonry can only provide major storm protection when fully grouted. Steel construction is not normally rated for windstorm protection.
For both systems, it can be costly to achieve more than code-compliant levels of energy efficiency, but significantly harder for steel construction than masonry. Masonry walls also contribute significant weight of material to a project, while steel construction requires many different materials to complete an assembly. Neither system provides any significant amount of recycled materials. Building lifecycles are usually good with masonry construction, yet only modest with structural steel.
With proper insulation and air barrier design, both systems can provide a reasonable level of air tightness and energy efficiency. However, it may be more difficult to achieve optimal performance from the steel cavity wall construction. Concrete masonry can provide better potential thermal comfort and noise reduction than steel construction, thanks to the insulation and thermal mass of the wall.
Continue reading in our white paper, Leadership in School Construction.