By Craig A. Hargrove, AIA
From The February 2017 Issue
With today’s strict energy conservation codes and increasingly complex facade and roof systems, many new construction projects involve the services of a building envelope design professional. This also applies to expansions and adaptive reuse. Making the best use of that consultant’s services is important not only to the bottom line of the project, but to the energy efficiency, code compliance, sustainability, integrity, and longevity of the building. When should a building envelope consultant get involved? What services should he or she be expected to provide?
By working with the design team to establish performance criteria for the building envelope, the consultant proposes materials and components to optimize efficiency across facade and roof assemblies. This specialist can identify ways to reduce costs with details that are watertight, thermally insulating, and correctly constructed; when amplified over the entire building, even small improvements can add up to substantial savings. Ideally, boosting exterior envelope performance can reduce the necessity for larger mechanical packages and mitigate the effect of energy consuming systems, such as lighting.
To realize these benefits, there are steps a building owner or design architect can take to get the most value from a building envelope consultant. The role of the envelope specialist changes throughout the design and construction process, and knowing when and how he or she should be involved can make a big difference to the project outcome.
Material And Assembly Specification
Because building envelope architects and engineers work exclusively with the outsides of buildings, they tend to amass substantial knowledge of facade and roof systems and their properties. Therefore, when it comes time to formulate and apply building envelope system criteria—whether budgetary, ecological, performance, or design—the envelope specialist brings key background experience in establishing parameters and identifying options for suitable envelope systems.
Recently, one of our engineers provided facade design consultation services for a new residential high-rise in Manhattan. In a city where space is at a premium, a central consideration for any developer is how to maximize interior floor space while meeting design and performance requirements for the facade. After evaluating energy code requirements and probable construction costs, the engineer was able to recommend a facade assembly to meet relevant energy efficiency requirements, but which was shallow in depth, maximizing apartment square footage.
With energy code often the prime directive driving design, balancing mechanical package efficiency with building envelope thermal resistance has become a central consideration. In order to achieve the requisite energy performance, design teams must offset an economical mechanical package with strict control of heat transfer across the building exterior. Working with the mechanical engineer, the envelope consultant provides options that consider the impact of exterior envelope design on the size and cost of heating and cooling systems.
As an example, consider fenestration design. Energy loss tends to be greatest at the edges of glazing, where inefficiencies of the frame transfer thermal load to the glass. By specifying warm edge spacers—low-conductivity materials used in lieu of aluminum to position the panes of insulating glazing units (IGUs)—the envelope consultant can mitigate heat loss across windows or glazed curtain walls. Even seemingly minor modifications like this one can improve thermal performance enough to permit downsizing of mechanical equipment, often netting both short- and long-term savings.
Green building projects can make the most of the building envelope consultant by involving him or her in the design phase, to brainstorm exterior wall and roof assemblies and to act as a sounding board for design decisions. Many government projects are now required to obtain certification from Leadership in Energy and Environmental Design (LEED) or similar rating systems. At the same time, municipal, state, and federal budgets are stretched thin. That’s where building envelope consultants really pay for themselves: by specifying components individually, rather than as a prefabricated system, the envelope specialist can handpick only those parts that are essential.
A recent new construction project at a military base in New England provides an excellent example of design collaboration between the architect of record and the envelope specialist. With a very tight budget, the project was expected to earn LEED certification by using efficient, well-designed envelope systems. Our building envelope engineer ran thermal computer models for a number of different roof assemblies, then provided options to the project team. We also advised on the integration of air and vapor barriers, particularly at facade/roof intersections. By optimizing configuration and type of insulation in the roof assembly, we were able to assist the design architect in maximizing efficiency while reducing construction costs. The project stayed within budget and earned LEED Gold certification.
Codes, Standards, Rules, And Best Practices
With the trend toward increasingly stringent energy codes and the push by organizations like the American Institute of Architects toward sustainable design and green building, the requirements for facade and roof performance are a moving target. Add to that changes to state and local building codes and constantly evolving green building certification requirements, and the design of even seemingly straightforward envelope elements becomes anything but simple.
To keep up with these changes, a design architect would have to spend a considerable amount of time on each project researching current codes and scouring industry literature for small details like air barrier terminations or sealant composition. The building envelope consultant is well positioned to do just that. With building exterior details as their focal point, envelope consultants can devote the time and attention it takes to stay abreast of current regulations and developments in facade and roof systems.
Cool roof technology is one example of an area in which building envelope consultants are particularly important to project success. As reflective and vegetated roofs become increasingly popular, architects are faced with the challenge of selecting, specifying, and detailing a system that meets performance requirements, falls within available budget, and is suited to the building structure, climate, and location. Well-versed in the pros and cons of waterproofing systems and roof membranes, the building envelope consultant can provide recommendations for a roof assembly that meets design objectives.
For reflective roofs, the envelope specialist can assist in deciding whether, for instance, a single-ply white sheet system or a modified bitumen assembly with reflective granular cap sheet would better meet stated performance objectives. Roofs used as public space raise still more questions, such as whether recessed terrace lighting might generate too much heat too close to insulation, or whether transformers can be exposed to the elements.
Vegetated roofs demand strict attention to waterproofing details, given that removing layers of plant matter and growing medium to search for a leak is labor-intensive and expensive. Getting the envelope consultant involved in specifying a resilient waterproofing system can provide owners with the reassurance that their lush green-roof amenity won’t turn into a leak-ridden liability.
It’s not uncommon for construction documents to be what one of our engineers calls “light on details.” Because roof and facade assemblies are often proprietary systems, designers tend to rely on manufacturers’ standard details. In the field, however, components don’t always work together as smoothly as they do on paper, with intersecting building areas and irregular dimensions that defy boilerplate drawings. These discrepancies can lead to change orders and delays.
Pre-construction, the building envelope consultant reviews drawings and specifications to evaluate or provide details, particularly at intersections, terminations, penetrations, and changes from one material to another. The envelope specialist redlines drawings and provides technical information, raising questions about the finer points of edge flashing, membrane tie-ins, fasteners, and construction sequencing that may be missing from or unclear in the design.
Some details might seem to work on paper, but would be difficult to construct in practice. While reviewing plans for an addition to a Washington, DC business school, our architects identified roof drain details that could be simplified, shortening construction time and also improving the longevity and functionality of the roof assembly. Details that might otherwise have been left to the contractor, such as attachment methods for copings and edge protection at changes in roof height, were addressed in advance, saving time in the field and improving outcomes.
During the contract documents phase, the building envelope consultant’s role shifts from providing options to preventing errors. Early in the design process, the envelope consultant looks at broad considerations of energy performance, code compliance, structural integrity, sustainability, and cost. Once the project team and the owner agree to move forward with a design, the consultant turns his or her attention to construction details.
Not long ago, an urban university added a glass-enclosed student center in an infill area between two historic academic halls. Elegant in its simplicity and innovative in the use of a dynamic facade, the building was featured in a number of architectural publications and was the recipient of a design award. Unfortunately, from nearly the day construction was complete, the building leaked.
Primarily, the flaw lay with the gutter system, the design of which had the unintended effect of channeling water toward the building, rather than away. As a result, the university spent additional time and money on the redesign and reconstruction of the entire roof drainage and gutter system. Involving an envelope consultant to evaluate facade/roof intersections and other key integration points might have prevented the failure, by correcting potential trouble spots before the project ever went into construction.
Working backward to determine the source of a problem—then forward again to solve it—is what gives building envelope design professionals the expertise to avoid those types of errors in the first place. After seeing the same types of detailing mistakes over and over again, building envelope specialists know what to look for, both in contract documents and in the field, to identify and resolve incipient problems.
Field Verification And Testing
Even after building exterior components have been installed, the envelope consultant remains an important part of the project team. Verifying that assemblies perform as designed, and that they are constructed in accordance with the contract documents, is another key role of this professional.
In one recent example, a popular hotel casino looked to add a high-rise addition to the existing guest accommodations, to be clad in a unitized glazed curtain wall assembly. With 156 glazed panels per floor and eight floors of curtainwall cladding, the building was set to have nearly 1,250 curtain wall units. Asked to review production and installation of the curtain wall system, our building envelope specialists discovered that fabrication of some of the panels was not dimensionally correct, leading to alignment problems during installation.
After sending the panels back to be deglazed and reconstructed, the owner positioned a full-time representative at the manufacturing plant, to improve organization and quality control. With the additional oversight of the envelope specialist, not only did product quality improve, but also production volume, rising from 25-30 panels per day up to 30-40. The increased output permitted the construction team to catch up with the original project schedule.
Once the new panels were installed, the building envelope consultant specified and oversaw air and water infiltration field testing to verify performance of the curtainwall system. The testing process involves specifying relevant protocols as per industry standards—most commonly, those published by the American Society for Testing and Materials (ASTM International) or the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)—identifying appropriate test locations, establishing performance criteria, and observing testing to see that it conforms with specified test methods.
For units that fail, the envelope consultant analyzes the test results and the relevant building elements to determine the probable cause and to recommend repairs. The modified assembly is then retested to confirm that it fulfills performance criteria.
In our high-rise hotel example, field verification and testing uncovered problems that might not otherwise have been noticeable until symptoms of distress and failure emerged.
The Big Picture
Perhaps most importantly, involving a building envelope consultant in a new construction project frees up the prime architect to focus on design development, without becoming bogged down with the intricacies of waterproofing detailing, component anchorage, or air barrier specification. Rather than expending the designer’s time on product comparisons and code research, the client can derive the most value from the prime architect by working with him or her to create a building that satisfies program requirements while achieving a desirable and, ideally, innovative and powerful aesthetic.
Green building designers are already responsible for creative solutions to the problems of energy consumption and resource depletion, making it all but impossible to simultaneously achieve fluency in roof wind load code requirements or best practices for face-sealed glazing systems. The services provided by a building envelope consultant are not a duplication of those performed by the architect of record; they supplement the design services that are common practice for a new construction project. Although it is not required that an architect provide details for every single roof termination, for example, it is enormously helpful in taking the guesswork out of installing the roof. The building envelope consultant fills in the gaps to help construction run as smoothly as possible.
To make the most of an exterior envelope consultant, it’s best to involve him or her early in the design phase. The envelope specialist can raise questions and identify potential problems while there is still ample time to correct them. With this sorted out ahead of time, construction delays may be less likely, saving money for the building owner and avoiding conflict on the project team.
During construction, the envelope consultant should be available to review shop drawings and submittals and to observe construction, identifying and responding to incorrect installation, poor workmanship, or unforeseen issues. Once systems have been installed, the envelope specialist can specify and oversee functional performance testing, such as air and water infiltration tests, to correct deficiencies that would otherwise result in leaks and premature deterioration.
Building systems are complex, and technical requirements are even more so. To adapt, project teams have become more and more specialized, with separate installers responsible for each proprietary assembly. Add the involvement of independent consultants for mechanical, electrical, plumbing, structural engineering, amenities, lighting, furnishing, sustainable design, renewable energy, urban planning, building codes, accessibility, etc., and it seems as though one more consultant is the last thing a project team needs. But the role of the building envelope consultant is not to look at one system in isolation; it’s to make sure that the exterior envelope—in consort with the mechanical and energy packages—works together as a whole.
The value in a building envelope specialist may be found in the details, but it also lies in bringing together the disparate systems that comprise a building’s exterior shell. The critical role a building envelope consultant performs, whether new construction or rehabilitation, is to make sure the building envelope performs as intended, and performs well.
Hargrove, AIA, LEED AP is senior vice president and director, architecture with Hoffmann Architects, Inc., an architecture and engineering firm specializing in the building envelope. As manager of the firm’s New York City office, he oversees the development of design solutions, both for new construction and for the rehabilitation of existing structures.
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