Building envelope assessments: From pre-design to construction
There are many aspects to a building envelope assessment and it’s crucial the consulting engineer takes them all into account.
When selecting components for the building envelope, several critical characteristics need to be considered, particularly for exterior walls: resistance to air leakage, water, structural performance, durability, security, seismic performance, movement and condensation are all examples.
It is important to ensure the facade and fenestration systems used to create them can withstand any number of concerns. From the natural (hurricanes/storms, earthquakes, extreme temperature) to the human-made (fires, bomb blast, noise), there are many of events and components exterior walls must be able to withstand. Assessing these fenestration systems in advance of construction can help ensure the right products are being used for the project at hand.
When assessing building enclosure materials, it is important to keep in mind the goal of the building envelope. Is it to be aesthetically pleasing? Meet U.S. Green Building Council LEED requirements? Is it purely functional? Is the project aiming for energy efficiency or other reliability concerns? When will the façade and fenestration systems be assessed for these characteristics? Assessments can be done in the pre-design, design, preconstruction or construction phase. Each has its own uses, but each is handled differently, so it is important to consider the phase along with testing needs.
Design considerations for building envelope
Pre-design considerations are made to ensure the enclosure reflects occupant use, climatic conditions, heating and cooling and life cycle expectations. It is important to understand what is wanted/needed and budget accordingly, establish the project performance requirements, compare design concepts to those requirements and use performance goals to make design decisions. During the design phase, critical decisions include selection of systems/components; review of construction sequencing and scheduling; assessing component/system integration and transitions, as well as system compatibility; considerations around workmanship dependency on performance; thermal modeling; hygrothermal modeling; and integrating performance requirements into design documents.
Once the project is in place and underway and materials have been selected and obtained, it can be critical to assess materials to ensure they really will perform as needed against natural and human-made events, sustaining durability, security, performance and other concerns. Evaluations can be run early in the construction phase or even once construction is underway. Early on, before construction starting, mock-up testing can provide valuable information.
A pre-construction mock-up is a full-size representation of the proposed exterior wall system built to study proposed construction details, test for performance and possibly judge appearance of the exterior wall system. A lab pre-construction mock-up is constructed and assessed to assess things like structure, air tightness, water infiltration (if any), condensation behavior, construction detail identification, construction method review, ability to address future problems/changes if needed, code compliance and job specification compliance.
When deciding what type of mock-up to test and what to include in it, include typical details for the job like an accurate representation of the wall design, specialty details and all anchorage types and conditions. Anchorage types and conditions will play a big factor in test chamber set up. These include support/end conditions, longest spans, corners and inside/ outside/other angles. System transitions, like curtain wall to panel or panel to brick, must also be factored in, as well as the building size and conditions. Architects, consultants, building owners and manufacturers can all play an important role in these decisions.
The pre-construction mock-up test chamber is representative of the project specific anchorage. The design, construction and placement of the test chamber is a very important process. All chambers are different. Test labs should use job drawings to design a representative test structure, attached to test walls that recreates the real job conditions. Always ask the lab to provide a set of chamber drawings for approval before construction begins.
Building envelope testing and certification
Once constructed, the mock-up will undergo a series of testing, including static air infiltration, static and dynamic water penetration, structural performance/wind loads, seismic and in some cases thermal cycling and condensation resistance. Data is compiled into a final report and this information can then be used to proceed with a project, make additional changes/adjustments or reassess the project needs and how they can be met.
Once construction has started, field testing can be performed to certify or validate product performance ratings. In such cases, installed products can be evaluated to verify performance and installation. Forensic testing may also be done on assemblies or structures with known water problems.
Common field tests include Fenestration and Glazing Industry Alliance AAMA 502 and AAM 503, which use air infiltration/exfiltration, per ASTM E783 and water penetration tests, ASTM E1105. Specialty tests can also be helpful to assess acoustics; thermal concerns; glass for bowing, warping and frost points; masonry anchors for shear and tension; structural performance; roof characteristics; and more. Specialty tests can be done for any number of reasons at different points in the project, such as early in the installation, different intervals of installation (5%, 50% and 90% done are typical); throughout the entire installation, before the installation of interior finishes, such as insulation, drywall, trims, etc.; and before project completion. The number of tests and when they are performed depends on the specific project.
There are many internal and exterior forces that act against the building enclosure, which is comprised of many components and systems. A high-performing building is achieved by understanding the acting forces, as well as the building enclosure components and by implementing a quality assurance program and conducting testing to verify performance. All of this leads to a critical understanding of the performance characteristics of a building’s exterior wall per the job specifications.
Test the unique façade conditions used on a job. Review project specifications before a job starts and test to mitigate risk before, during and after construction. This will help ensure project success and satisfaction.