Building Enclosures - Getting Them Built Correctly

Transcription

1 Building Enclosures - Getting Them Built Correctly Michael F. MeLampy KTA Tator, Inc. Manchester, Ma mmelampy@kta.com Synopsis Building enclosure construction now includes many different materials placed in many different layers by, at times, many trades. Because of all the players now involved, the potential for errors has increased. With the many different sections of a contract that concern components of the building enclosure, it is difficult for each trade to know how his work effort may affect the overall functioning of the enclosure. This, in addition to the numerous different materials being used, and the possibility of chemical and physical incompatibility between these materials and other adjoining materials and components, means that the potential for failure of one or more building enclosure components increases and the owner has the potential for an uncertain future. The project general contractor must provide an active effort to assure errors are prevented and/or fixed or, at the least recognized and corrected as they occur. The importance of a building enclosure preconstruction meeting is apparent. The meeting should be attended by all trades involved in order to review the accepted shop drawings and to review and discuss the construction sequence. In essence Who does what and when? Each trade needs to have a quality control process that will insure proper assembly of each component, and the general contractor s quality control process that will ensure the proper assembly of the entirety of the building enclosure. These quality control processes should be reviewed by the Building Enclosure Commissioning Agent (BECA) to determine that they provide for suitable quality control effort(s). The concept of retrocommissioning as it relates to the building enclosure is exceedingly expensive and should only be performed where building construction defects have yielded unacceptable conditions for the building inhabitants or where building operation costs are extreme. During construction an independent BECA provides quality assurance oversight of the contractors approved quality control processes. This additional effort will improve the owner s and architect s confidence that the construction process will provide the desired product, both in the near term and over the projected life of the building. Using the Brain and Cognitive Sciences Center (BCSC) at Massachusetts Institute of Technology in Cambridge, Massachusetts as a case study, this paper will discuss how the commissioning procedures described above were utilized to ensure that the as-installed building enclosure would provide its designed functions. This paper will discuss typical quality assurance oversight techniques and present typical spot testing and inspection procedures to help assure that the MeLampy: Building Enclosures: Getting Them Built Correctly 1

2 contractor s work process provides for an enclosure that conforms to the owner s requirements. This project was of high importance and of high visibility. Construction deadlines and difficult construction details added to the opportunities for nonconforming work product and most importantly a building that would not perform as designed The Building The 400,000 square-foot Brain and Cognitive Sciences Center (BCSC) at Massachusetts Institute of Technology in Cambridge, Massachusetts combines three different research groups to create a world-class brain research center. Designed to include both wet and dry laboratories for research, biology, biochemistry, neurobiology, and behavioral and cognitive research, the BCSC is a teaching and learning center. The building itself includes a day-lit multi-story atrium containing meeting rooms, offices and seating areas for interaction among the scientists. Design Figure 1 - Various façade components, curtain wall, windows and limestone cladding Much of the building exterior is clad in large imported Italian limestone offset by windows that were placed flush to the exterior. A section of curtain wall was also a part of the enclosure. A live railroad track and active transit corridor pass through the building at ground level. The building bridges this transit right-of-way to create a single unified structure. As part of MIT s commitment to sustainable design, the building incorporates various strategies to reduce energy use and improve resource preservation. A high-performance building enclosure, grey water MeLampy: Building Enclosures: Getting Them Built Correctly 2

3 recovery, heat recovery from exhaust fans, and daylight utilization contribute to the overall integrated design approach. Figure 2 Live railroad tracks through building. Note various façade components, and adjacent urban structures The High Performance Building Enclosure System The high performance building enclosure system provides four key functions for the building: A thermal barrier to provide insulating properties to save energy A vapor barrier to prevent the diffusion of moisture through building materials Drainage planes to effectively manage water infiltration An air barrier to control the movement of air throughout the building envelope All of these functions are important to both the long life of the building enclosure and occupant comfort. Many of these functions are commonplace, with the exception of the air barrier which is a newer technology in the United States and is now a part of the Energy Code in Massachusetts. An air barrier is used to control the movement of air across the building enclosure or between environmentally separated areas within a building To best define the air barrier, it is important to note the difference between air barrier materials, air barrier assemblies and air barrier systems. An air barrier material is an individual product or material that blocks or restricts the movement of air. An air barrier assembly is an assembly of air barrier materials, like a window/wall junction. An air barrier system is the overall system made up of many materials and assemblies providing for an airtight building. A building enclosure includes the roof, walls, fenestrations, and below ground materials that separate the building from its surrounding environment. Environmental separation may also MeLampy: Building Enclosures: Getting Them Built Correctly 3

4 include walls between rooms which have different conditioning requirements such as a swimming pool area and an ice hockey arena. Air barrier systems combine various materials and assemblies, creating a barrier to air leakage through the walls to provide the required environmental separation. Typically, and as per the Massachusetts Energy Code, the air barrier must have the following characteristics: Airtightness Individual materials designated as the air barrier must have an air leakage rate no greater than cfm/ft 2 under a pressure differential of 0.3 in. water (1.57 lb/ft 2 ). Continuity The air barrier system must be continuous on all six sides of the building. That is, it must extend over the walls, roof, and below the ground, and from the opaque wall through the window frame to the glass, and back through the window frame to the opaque wall. This holds true for all penetrations through the building enclosure such as doors and skylights. Structural Integrity The air barrier system must be able to withstand the loads that it can be reasonably expected to encounter, transferring these structural loads back to the structure of the building. These loads include including wind load, stack pressures, and creep loads. Durability If the air barrier is placed in the wall system where it cannot be maintained it must be must be durable; that is, it needs to last the life of the building enclosure. If the system fails, building components may become displaced and/or lose their functionality. If the air barrier is accessible it must be maintained by the owner. In this building the air barrier was considered non-accessible and as such must be built in a durable fashion. Air barrier functionality is critical in buildings which necessitate a strict control of interior conditions. Additionally, an air barrier can act to help reduce the amount of energy used by the building and the energy costs for conditioning the air (including heating, cooling, humidifying and dehumidifying) within the building. Despite the benefits of an air barrier system, the lack of a well constructed and functioning system can lead to damage of building envelope components. This damaging process can be amplified when the components are under constant exposure to interior conditions such as high pressure, humidity, or temperature that can increase the differential that exist between the interior and exterior sides of the wall. Given the highperformance requirements of the BCSC building enclosure system, and the Massachusetts Energy Code, it s necessary to incorporate a cost effective and constructible air barrier system into the design. As such, it was important to meet the requirements for airtightness, continuity, structural integrity and durability. The air barrier materials also had to function in conjunction with other building enclosure materials including the roofing system, curtain walls and windows to create a continuous airtight enclosure over the entire structure. Air Barrier Material Selection Process Numerous air barrier materials and systems were available for this project, including bitumen peel and stick sheet membranes, liquid applied membranes, spray applied urethane foams, and rigid boards. The first decisions that had to be made concerned what family of materials would be selected. Each of these products had individual benefits and constraints. Due to the high performance requirements of this monumental building and the desired long life, the architect specified the material options to include bitumen peel and stick membrane, liquid-applied membrane and spray urethane foam. A mockup was built so that each material could be evaluated. Each of these products could, when properly applied, provide a structurally sound, durable and airtight barrier. Due to expected substrate irregularities, compatibility with insulations systems, tight constraints of the cavity wall and ease of application, the spray applied MeLampy: Building Enclosures: Getting Them Built Correctly 4

5 liquid membrane was chosen by the general contractor for this project. Peel and stick membranes were used as a transition material or to tie-in the different assemblies such as windows, control joints, and roof wall junctions. In all cases, the other joints and juncture materials such as mastics sealants and caulking would need to have compatibility with these products. Figure 3 shows the mockup wall, with peel and stick material (black) used in conjunction with the liquid sprayapplied (pink) material. In Figure 4 a light green spray-applied urethane foam material is shown on the same (right-hand side) mockup wall, with a peel and stick material used beneath the spray foam at joints and junctures. Insulation board was mounted over the peel and stick and liquidapplied material on the left. Figure 3 Mock-up peel and stick membrane (black) liquid spray applied material (pink) Figure 4 Mock-up spray urethane foam and insulation board air barrier. Construction Air barriers are designed to work in a specific fashion and building trades people may need to be additionally trained to understand all of the aspects of air barrier system, and its installation. As such, great attention was given to application details during the training. Expectations had to be clearly understood. Pre-job/installation meetings (or an orientation meeting) were held to determine the installation procedures and to address who, what, how, and when. This was essential as there were several trades involved with each of the various components. As an example, a mason s work effort can aid or greatly hinder a membrane detailer s work, based on how flat the mortar joint is struck. Other examples include the work of the window glazer and how the windows are fastened into the wall, how much of a gap exists between the window and the wall, and how and when are flashings to be installed. Specific issue meetings took place when a new issue or problem were encountered, such as new window frame edge type, placement of insulation, and proper detailing around stone anchors. These issues or challenges often required field trials and the development of new work practices. Good communication was MeLampy: Building Enclosures: Getting Them Built Correctly 5

6 essential amongst the various trades, the general contractor, the owner, the BECA (or quality assurance firm), and the architect in order to provide a project without the need for rework or reconstruction. Figure 5 Spray application of air barrier membrane Figure 6 Peel and stick detailing at window fenestration and at horizontal and vertical control joints Figure 7 - Spraying liquid applied membrane to the self adhered membrane, window and horizontal control joint detail MeLampy: Building Enclosures: Getting Them Built Correctly 6

7 Quality Assurance A comprehensive inspection and testing quality assurance protocol was developed by the Building Envelope Commissioning Agent. This included visual observations of the construction process during installation together with various in-process and post-installation tests. The visual observations were used to ensure that the construction process. Work plans that provided a properly installed and functional building enclosure were repeated throughout construction. The visual inspections focused on the spray-applied material to look for defects in film formations such as pin-holes and visible holidays so that any issues would be repaired and/or resolved before additional air tightness testing was performed. Monitoring of ambient conditions was necessary to ensure the material was applied within specific temperature and humidity conditions as per specification requirements and manufacturer s recommendations. Wet film and dry film thickness measurements were made on the liquid spray-applied membranes to confirm that the specified (minimum) thickness of membrane had been applied. In this situation the liquid-applied product was 100% solids and showed no shrinkage during the curing process. The resultant dry film thickness was closely approximated by measuring the wet film thickness. Occasional dry film thickness measurements were taken for verification purposes. Dry film thickness measurements were made by removing sample and measuring with a micrometer. Tensile strength of adhesion between the membrane and substrate was tested in general accordance with ASTM D 4541 Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers. The membrane was required to withstand a minimum tensile load of 16 pounds per square inch, applied perpendicular to the test area. Occasionally, test results and visual observation required the contractor to reapply the peel and stick connective and detailing material due to low adhesion, while the spray applied material to the substrate generally exceeded specification. Figure 8 - Adhesion testing The overall airtightness of the opaque wall system was randomly verified using a combination of visual examination and qualitative and quantitative testing practices. ASTM E Standard Practices for Air Leakage Site Detection in Building Envelopes and Air Retarder Systems and ASTM E 783 Standard Test Method for Field Measurement of Air Leakage Through Installed Exterior Windows and Doors were used to evaluate the airtightness and site detection of air leakage locations of both individual details and assemblies. Whole building testing was not possible due to the size of the building. MeLampy: Building Enclosures: Getting Them Built Correctly 7

8 Qualitative airtightness testing was performed in general accordance with ASTM E 1186, which provided go or no go test results. The test procedures allowed the QA Technician as well as the air barrier contractor to visibly evaluate airtightness. Two methods were used. Method Figure 9 - ASTM E 1186 testing, Method Tent around window fenestrations - view from inside looking toward window Smoke Leaking through the joints and junctures MeLampy: Building Enclosures: Getting Them Built Correctly 8

9 Figure 10 - ASTM E 1186 Testing, Method Smoke indicates air leakage at or around window frame utilized a pressurized tent enclosure on the inside or outside of the building. A chemical smoke was added to the tent, with the technician looking for leaks on the opposite side of the wall. Method utilized a hand-held depressurization dome and the topical application of leak detection liquid. If the technician saw bubbles in the leak detection fluid once depressurization had begun, leaks were present. This test method was used for small confined testing areas. Both of these tests were used at low pressures, Pascal for method and Pascal for method 4.2.7, mimicking the type of air pressure that the building might experience. The higher pressure used for method was required to sufficiently displace the surfactant to detect smaller air leaks. MeLampy: Building Enclosures: Getting Them Built Correctly 9

10 Figure 11 - ASTM E 1186, Method Technician looking for indications of air leakage around sample stone anchors The quantitative test method as defined in ASTM E 783 was used to determine air leakage values at and around window/wall assemblies. To conduct the test, an airtight box/chamber was constructed over the test area. The test chamber itself was evaluated for airtightness using ASTM E 1186, Method Once verified, various air pressures were introduced into the chamber and air flows calculated. These air flows, representing air leakage over the test area, were checked for conformance with the specification. This test was performed only in areas as selected by the owner. The ASTM E 1186 test also indicated where these leaks were in the test area. MeLampy: Building Enclosures: Getting Them Built Correctly 10

11 Figure 12 ASTM E 783 Quantitative Testing Test chamber being constructed over window fenestration and stone gravity anchors Figure 13 - ASTM E 783 Quantitative Testing Technician adjusting air pressures and recording air flows MeLampy: Building Enclosures: Getting Them Built Correctly 11

12 The thermal barrier or insulation was of additional concern. Proper application required that the stiff extruded polystyrene insulation board be in contact with the air barrier. The specification required the insulation board be adhered to the air barrier material. Due to the irregularities in the substrate surface resulting from standard tolerances of construction, the board often lifted off the wall. This was a problem as convection currents can cycle behind insulation cavity reducing the insulating properties. As a result the contractor altered the installation process using a different adhesive and cutting the boards to fit the different wall profiles, so the board was not bent to fit the wall. In some cases mechanical fastening of the board to the wall was required. All gaps and voids in the insulation were filled and sealed with spray foam insulation These alterations to the construction process allowed for a completely insulated building. Figure 14 - Insulation board not in contact with wall Figure 15 - Mechanically fastening of insulation board The air barrier and thermal barrier required special construction processes at locations where the one-piece stone anchors were mounted. This process required drilling through the air barrier and masonry to mount the angles. The process required that a sealant be applied to the hole and bolt during installation. After the angle was mounted, the insulation material was fitted around the bolts and adhered and sealed with spray foam. The water barrier or drainage plain properties on this project were performed by the air barrier materials; the continuous, airtight air barrier was designed and installed to block the flow of liquid water in addition to blocking the flow of air. The air barrier material was also designed to provide vapor protection, and as such it was placed on the warm side of insulation. The selected air barrier material met the vapor permeance requirements as outlined in the Massachusetts Energy Code. By assuring the required thickness of the air barrier membrane material the vapor barrier requirements were met. Conclusion The MIT Brain and Cognitive Sciences Center project is a premier example of a liquid-applied air barrier being used as a critical high performance component within a building enclosure for environmental control. This building is designed not only to be a world-class research center, but also as a monument and landmark for Cambridge and MIT. MeLampy: Building Enclosures: Getting Them Built Correctly 12

13 Figure 16 - Stone Anchor Assembly It is good practice to have a Building Enclosure Commissioning Agent involved in the process. The wall is actually the outer reaches of the buildings mechanical systems and must be properly constructed to ensure that the HVAC systems can function as designed. Who, how, what and when are important issues, which if not properly planned can lead to delays, cost overruns, rework, and/or possible premature building enclosure failures. In-process quality control by the contractor and the sub-trades should be required as well as independent third party Building Enclosure Commissioning or quality assurance. This is important to assure that a reliable, life of the building, building enclosure has been installed; one that will meet the requirements of the specification, and the needs of the building and the owner now and over the life of the structure. MeLampy: Building Enclosures: Getting Them Built Correctly 13