Medical Construction & Design

JUL-AUG 2015

Medical Construction & Design (MCD) is the industry's leading source for news and information and reaches all disciplines involved in the healthcare construction and design process.

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Page 29 of 70

Science of color The study was implemented in the Lower Mainland of British Columbia, Canada. It examined and measured three dif erent colors of roof membranes (white, gray and black) installed on three insulation assemblies, totaling nine unique test roof segments. The three insulation strategies tested were polyisocyanurate (double layered), stone wool (double layered) and a hybrid combination of a layer of stone wool over the top of a layer of polyisocyanurate. Each roof combination provided equally insulated insulation strategies ( by manufacturers' published R-value) and measured 1,600 square feet in size over the same building and indoor conditions. The insulation portion of the study was to measure the insulation performance of each roof over time and as temperatures varied. Sensors were installed within each of the nine roof samples that measured thermal resistance, along with relative humidity, moisture, heat f lux and dimensional stability throughout a range of in-service temperatures. The findings were persuasive. The roof assembly insulated exclusively with stone wool insulation (measuring 5.75 inches), demonstrated to have a more stable R-value, which increased at colder temperature and was not susceptible to a loss in R-value over time. Both the stone wool and hybrid roof assembly systems demonstrated R-values close to calculated values, while the polyiso assembly dropped at temperatures above and below the 75 F mean. The R-value loss in the polyiso can be attributed to blowing agents, which may condense (change from gas to liquid) in cold conditions, resulting in decreased R-values. In the RDH study, while stone wool proved the top performer, the hybrid assembly, consisting of 2.5 inches of stone wool insulation over 2 inches of polyiso — roughly 45 percent of the total R-value — demonstrated a significant improvement in the effective R-value over the polyisocyanurate-only system. The stone wool top layer protected the polyiso from temperature extremes and of ered noticeably improved R-values in cold and hot conditions than the polyiso roof. The hybrid combination was only slightly thicker than the polyiso roof, and the increased performance leads to more stable R-values and less dimensional movement. R-value stability will provide greater occupant comfort and more predictable energ y ef ciency throughout the life of the building. Benefi ts of hybrid roofs Stone wool insulation, being higher density, has a higher thermal mass than foam plastic insulation, and it acts as a heat absorber as roof temperatures can vary dramatically over the course of a day. The research found that the systems incorporating stone wool had lower heat fl ow measurements, interior surface temperatures and membrane cap sheet surface temperatures. The decrease in peak membrane temperature is also thought to slow the heat-related deterioration of the roofing membrane, potentially extending the service life of the roof membrane. Sound absorption is another important consideration to take into account in medical building applications. A calm, quiet and peaceful setting is necessary for both patients and medical practitioners. The higher density of stone wool insulation in a hybrid system helps to reduce airf low and contributes to good acoustical performance. Non- directional fiber orientation aids in the absorption of acoustic waves and can reduce the intensity and propagation of noise. Fire safety and the building codes enacted to protect occupants are particularly critical in medical construction due to the extreme vulnerability and, in some cases, limited mobility of the patients inside. Roof assemblies are a component worthy of consideration in a building 's overall fire protection plan. Combining non- combustible materials, like stone wool, that do not add fuel to an existing fire, that do not contribute to toxic smoke and that may provide additional time for evacuation, is optimal. Thus, a hybrid system utilizing stone wool can provide valuable advantages when it comes to safety. Indoor air quality is another case in point. It is essential to specify products resistant to mold, mildew, bacterial growth and rot. In this case, a hybrid system is ideal, as stone wool's inherent properties make it naturally water repellant and moisture resistant. When it comes to energ y ef ciency, a roofi ng assembly with stone wool allows for more precise costing models for heating and cooling using reliable resistance values, which take into account climate-driven variables (the understanding that thermal performance is af ected by dif erent temperatures, environmental conditions and local climates), as well as dimensional stability. Accurately projecting (and potentially minimizing) operating expenses is a key concern in hospitals and medical facilities. In a hybrid system, the dimensional stability of stone wool plays a crucial role, preventing expansion and contraction problems and avoiding heat transfer and energ y loss as a result of gap formation, common with foam plastics. According to the article "Effects of Mechanical Fasteners and Gaps between Insulation Boards on Thermal Performance of Low-Slope Roofs" in the Journal of Thermal Envelope and Building Sciences (April 2000 issue), 1-inch- wide gaps in a two-layer insulation config uration reduced a roof 's thermal resistance by as much as 10-15 percent. Conversely, stone wool has one of the lowest expansion coefficients among all types of insulation materials. Thus, a hybrid system that capitalizes on the dimensional stability of stone wool protects against any potential initial shrinkage in the polyisocyanurate insulating material, ensuring integrity of the air barrier. "Overall, a hybrid roofi ng system lends many advantageous attributes to medical design and construction," said says Mike Benetti, senior segment manager, Commercial, with Roxul Inc. "It combines the high R-values of polyiso with the high performance of stone wool — from fi re safety, stable indoor air quality, sound reduction, energ y ef ciency and environmental responsibility. The result is an impressive solution that is quickly gaining traction." To view the full fi ndings on the RDH Building Engineering Ltd. study, visit Andrew Lindley is the commercial marketing product specialist at Roxul Inc., Milton, Ontario. Spotlight building envelopes light Spotlight MCDM AG.COM | J U LY/AUGUST 2015 | Medical Construction & Design 25

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