(JBED) - Summer 2006 - The Whole Building Design Guide

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could consist of lites that have different thicknesses. For example, one lite might be 1/4-inch thick, while the other might be 3/16-inch thick, resulting in a 9/16-inch airspace. Laboratory test data indicates that this glazing unit can achieve a slightly higher STC rating of 37. This is attributed to a reduction of the resonance of the system by using the different thickness lites. However, it is interesting to note that this window achieves the same OITC rating (OITC 30) as the previous 1-inch insulated glazing. This would suggest that the increased performance indicated by the improved STC rating may not be noticeable to an occupant, if the exterior noise source is similar to the OITC standard spectrum. Insulated glazing unit with laminated glass: Another alternate of the 1- inch thick insulated glazing unit could comprise one lite that is laminated. The laminated lite could be 1/4-inch thick and be used in combination with another 1/4- inch thick lite separated by 1/2-inch to create a 1-inch thick glazing unit. Laboratory test data achieves an STC rating of 39. This is also attributed to a reduction of the resonance of the system by using the laminated pane, which is a damped system. As with the previous example, it is interesting to note that this window achieves only a slightly improved OITC rating (OITC 31). The perceived difference of this glazing unit compared with the previous examples may not be noticeable to an occupant. Of practical interest, it is recommended that for acoustical reasons the laminated lite be installed on the interior of the glazing unit. This arrangement allows the lamination to remain closer to the occupied temperature, at which the lamination performs more effectively. Laminated panes that are subjected to colder temperatures perform similarly to non-laminated panes of glass. Insulated glazing unit with larger airspace: When the thickness of the window unit can exceed 1-inch, other options are possible for improving the sound isolation performance. For example, a 1-inch deep airspace between two 1/4-inch thick lites can improve the acoustical performance to a rating of STC 37; the OITC rating remains at 30, indicating that the perceived difference to the occupant may not 28 Journal of Building Enclosure Design be significant. The drawback of such a system is that the thicker insulated window unit may require a different (potentially non-standard) framing system to install this glazing unit. As a result, this may not be a cost-effective improvement to consider. “Storm sash” upgrade: In many remedial projects, it is not possible or costeffective to remove the existing window to improve the sound isolation. Many times the most effective solution is to introduce a secondary window system that captures an airspace of two-inches or more with respect to the existing window. Many people consider such an additional window akin to a “storm sash”. This type of upgrade can be performed on the exterior (if space allows) or interior (if the exterior of the building cannot be modified). With this upgrade, the airspace between the existing and new windows is a significant factor that largely determines the amount of sound isolation improvement that may be possible. It is suggested that airspaces of two-inches are the least that should be considered, but larger airspaces can provide even greater benefits. The thickness of the secondary sash is generally not considered as significant a factor. Testing on a recent project demonstrated that with an airspace of 5 inches, a 1/4-inch secondary pane was the most cost-effective upgrade to implement 2 . The acoustical performance of systems that include the secondary sash can start at STC 40 and OITC 33 and may even achieve higher sound isolation performance depending on the construction of the façade, depth of the airspace, or thickness of the secondary glazing. Potential issues to consider with upgrades: Acoustical upgrades to window systems can occasionally introduce the following detrimental effects: trapped condensation, thermal performance reductions, the need for heat treating of glazing, and difficulty in cleaning. Trapped condensation can result in any window systems that are not well sealed. This results from humidity entering the airspace between the two panes of glass and condensing on the cooler surface. The magnitude of the condensation is dependent on the humidity and temperature differences across the glazing system. It is occasionally possible to control this effect by using the building’s HVAC system to maintain a lower humidity level. Alternatively, it is also possible to introduce passive airflow vents for the cavity between the window system to maintain airflow that will minimize the condensation. The thermal performance with a secondary window system can decrease with larger airspaces. This is due to convection within the cavity transferring more of the heat to the colder surface and with a larger airspace, the convection can become more effective. Studies have shown this convection can reduce the thermal effectiveness of the window system. Airspaces between windows can trap heat that may build up to excessive levels within the cavity. As a result, manufacturers and installers often recommend heat treating the lites that create the cavity. This heat treating introduces a residual surface compression in the glass, which improves its ability to resist breakage from thermal stresses [citation WBDG]. The drawback of heat treating is the additional cost for the project. A practical issue with acoustical upgrades relates to cleaning the cavity between the two window systems. Typically, installed secondary window systems are not sealed and therefore present the potential for dust and dirt to enter the cavity. To clean within this cavity, it is necessary to allow for the secondary lite to be operable or removable. It is important to devise or select an operable or removable system that maintains a reasonable seal around the secondary sash when it is not being cleaned. Tests have demonstrated that cam locks and continuous hinges can provide the means to allow for the secondary sash to be operable and maintain a good acoustical seal. 3 CASE STUDIES The following case studies all involve acoustical upgrades of window systems. They include projects at an extended stay hotel in an urban setting, commercial office space under a runway departure, and a residential development under a runway departure. Extended stay hotel in an urban setting: The patrons of the hotel were complaining of being awakened by construction activities in the neighborhood,
which began early in the morning. They were also complaining of late night bar patrons causing a commotion when they left the bars in the late evenings and early mornings. The hotel did not want to have any more disappointed guests or continue to foot the bill for refunds. The existing window systems consisted of operable double hung aluminum windows with 1-inch thick commercial grade glazing. The dimensions of the windows were about four feet wide by about four feet tall. The windows were mounted within sills that included an additional five inches inside the guestroom. The exterior of the building was an old masonry construction within interior stud framing and drywall. This substantial façade construction meant that the sound isolation weakness was the windows. The deeper than average sills provided a good amount of space for mounting secondary window systems inside the guestrooms. With this arrangement, the exterior of the building was not impacted visually, which helped the project avoid any review by the local architectural board. Testing after the installation demonstrated a substantial improvement of the sound isolation. The overall noise reduction was measured to be approximately 7 to 10 dB better, which was perceived to be a noise reduction of 35 per cent to 50 per cent. This dramatically reduced the complaints from the guests, which greatly satisfied the hotel managers. They now market their guestrooms as providing superior sound isolation from the surrounding urban environment. Commercial office space under a runway departure: A new commercial office building was constructed in an area that had been previously used for industrial facilities. The site was less than one mile from a runway with the departure flight track passing directly over the building. Shortly after initial occupancy, tenants began to complain about noise. The noise from the departures was interrupting phone conversations and meetings. The developer requested a sound isolation upgrade that would provide effective sound isolation, but, at the same time, be as affordable as possible. A study of the noise impact yielded interesting results. It was learned that the runway operated infrequently under unique wind conditions that occur mainly in the spring and fall. In total, the runway was used for only about 15 per cent of the departures during the year. While this infrequent usage may seem to be a benefit, it was actually a detriment since it resulted in very intense use during those short periods. When these unique prevailing winds occur, every departing flight would use this runway, which meant that aircraft were passing over the site approximately every three to five minutes. This frequent departure schedule was particularly distressing to the tenants. Another interesting find from the complaints was that the noise was most bothersome on the side of the building that saw the backside of the planes as they departed; the occupants who would watch the planes approaching the building were not adversely impacted by the noise of the overflight. There were several significant issues relating to implementing the upgrades. The recently completed building was already partially occupied at the time of this work. This presented complications for accessing the windows, performing the upgrades and scheduling the work. Fortunately, the second of the two building that comprised the project was still in design, so the window upgrades being considered could be incorporated in the construction plans from the start. The base building windows were a 1- inch thick insulated glazing unit in individual window frame systems, or in two sections of curtain wall. The exterior façade of the building consisted of masonry with an interior stud construction, resulting in a fairly effective sound isolating construction. To determine the most cost-effective upgrades, in-situ testing was proposed with three different potential upgrades to be considered. The 3 interior sash options that were tested included a 1/4-inch thick annealed lite, a 1/4-inch thick laminated lite and a 3/8-inch thick annealed lite. A secondary framing system was installed within the existing window system to allow for quick changes between the various options. The frame was located where it achieved an airspace of five-inches from the base building windows. The tests included cam locks and a continuous hinged installation for facilitating the removal of the secondary lites. The test results demonstrated that the various options performed relatively similarly. The 1/4-inch thick annealed lite achieved an improvement of about 10 dB, while the 1/4-inch thick laminated lite achieved a reduction of 11 dB, and the 3/8-inch annealed lite provided a 13 dB improvement. The contractor assisted with pricing the various options. The developer eventually determined that the 1/4-inch annealed lite provided the most cost-effective option to implement. The tests also demonstrated that the cam locks provided slightly better performance over the continuous hinges. Based on the locations of the complaints, the upgrades were only performed on the two façades that faced the departing jet exhausts. The same upgrade was planned for the future office building project during the design. Residential Development under a Runway Departure: A new residential development was planned near the office building project described above. Based on the experience at the office buildings, there was significant concern with locating residences in this area. The most significant concern related to the potential for sleep disturbance due to late night or early evening aircraft operations. There was also concern about interference with conversations and listening to TV and music. Unlike the office buildings, the developer was required to demonstrate that their project would achieve an interior sound level goal recommended by the Federal Aviation Administration (FAA). The goal was to achieve a yearly daynight average sound level (abbreviated L DN ) of no more than 45 dBA. The airport’s own noise contours indicated that the proposed residential site was exposed to yearly day-night average sound levels exceeding 70 dBA. There were several complicating issues for this project. First, the annualized average sound levels do not take into account individual flight events. It is entirely possible to achieve the L DN 45 goal and still have significant sound levels intruding on the residence from individual departures. It was estimated that sound levels of 70 dBA were possible from louder aircraft departures. This sound level could result in sleep disturbance issues for the Summer 2006 29
Page 1: JBED Summer 2006 Journal of Buildin
Page 6: Message from NIBS David A. Harris,
Page 10 and 11: Feature Dynamic, Integrated Façade
Page 12 and 13: 1. COMMERCIALLY AVAILABLE SOLUTIONS
Page 14 and 15: procure them for the final building
Page 16 and 17: obstruction and/or daylight reflect
Page 19 and 20: Feature All That Glass Is there an
Page 21 and 22: façade at the street corner. It is
Page 23 and 24: cess to the perimeter, concrete str
Page 26 and 27: Feature Architectural Glazing for S
Page 30: esidents. Another concern from the
Page 33 and 34: from the California Central Valley
Page 37 and 38: Feature Window Comfort & Energy Cod
Page 39 and 40: By Valerie L. Block and Tammy Amos,
Page 41 and 42: Feature How Does Fenestration Fit I
Page 43: Council (ICC), one might expect tha
Page 46 and 47: Industry Update By James C. Benney,
Page 48 and 49: BEC Corner HOUSTON-BEC By Andy MacP
Page 50: Buyer’s Guide AIR BARRIERS Dupont

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