This webinar is sponsored by the Academy of Architecture for Health (AAH) on May 9, 2017 from 2–3pm ET. Earn 1.0 AIA LU/HSW. This presentation is a primer on building science as it relates to the exterior enclosure with particular emphasis on the air barrier. Air barriers play an important...
- Building Science Basics Enclosure Problems Building Science Basics Overview Involved in all aspects of the building enclosure design Principles relate to structures everywhere Key to understanding moisture problems Primary goals are to reduce energy costs & prevent moisture problems Building Science Basics Overview • Air movement • Air barriers • Drying and moisture transport • Heat energy movement • Insulation effect & placement • Material conductivity • Moisture problems • Water leakage • Vapor diffusion Building Enclosure Fundamentals Air Barriers for Health Care Facilities Air Barriers Air Movement & Barriers Air Flow Concepts Air Movement • High to low pressure • Pressurization affected by: – Wind effects – Mechanical systems – Stack effect • Transports: Heat & Vapor Air Movement & Barriers Wind Pressurization • External Pressures – Windward – Leeward • Internal Pressures – Positive and negative pressure – Affected by: Building type (open, closed, partially enclosed) External Pressures Internal Pressures (per ASCE 7) Enclosure Classification (Gcpi) Open Buildings 0.00 Partially Enclosed Buildings +/- 0.55 Enclosed Buildings +/- 0.18 Windward Pressure Leeward Pressure WIND Air Movement & Barriers Mechanical Pressurization Exhaust Negative Internal Pressure Outside Air Air Movement & Barriers Mechanical Pressurization Positive Internal Pressure Outside Air Exhaust Air Movement & Barriers Mechanical Pressurization Return Air (Vent Restricts Airflow) Fan Vent SupplyReturn Air Movement & Barriers Mechanical Pressurization Stack Effect: Hot Climate COOL Stack Effect Air Movement & Barriers Mechanical Pressurization Stack Effect: Cold Climate WARM COLD Stack Effect Air Movement & Barriers Barrier Definition Air Barrier Materials assembled and joined together to provide a barrier to air leakage through the building envelope. An air barrier may be a single material or a combination of materials. - 2015 IECC Air Movement & Barriers Air Barrier Requirements Continuous across thermal envelope Joints & seams sealed. Penetrations caulked, gasketed, or sealed Seals & detailing must resist positive and negative pressures Penetrations must not affect integrity of air barrier (e.g., recessed light fixtures) Air Movement & Barriers Air Barrier: Code Requirements • International Building Code • International Energy Conservation Code • ASHRAE 90.1 – Energy Standard for Buildings Except Low-Rise Residential Buildings Climate Zones Air Movement & Barriers Air Barrier: Code Requirements 2015 IECC Figure C301.1 Air Movement & Barriers Code Requirements – Building Envelope • 2000 – Leakage rates for fenestration & openings but no opaque criteria. • 2006 – Envelope is to be sealed to limit air infiltration. • 2012 – Continuous air barrier required throughout the building envelope (except Climate Zones 1, 2, and 3). • 2015 - Continuous air barrier required throughout the building envelope (except Climate Zone 2B Air Movement & Barriers Code Requirements – Opaque Envelope Allowable air leakage at 0.3 in. w.g. (75 Pa) Material: 0.1 perm 1.0 perm <=10 perm Additional Considerations Vapor Diffusion • Very slow process (less than airflow) • Vapor retarders control diffusion • Can be combined with air barrier and/or moisture barrier • Should be located on the “warm” side of the wall • Only one vapor retarder per wall assembly Additional Considerations Vapor Diffusion Common Vapor Retarders: Polyethylene film Fluid-applied vapor retarder Self-adhering sheet membranes Aluminum foil/FSK “Smart” vapor retarders Other Materials that Serve as Vapor Retarders Oil and epoxy based paints Polystyrene board insulation (XPS) Vinyl wall coverings Sheet metal & glass Additional Considerations Vapor Diffusion Insulation in Stud Space Hybrid System Insulation in Cavity “Cold” Climate “Hot” or “Cold” Climate Additional Considerations Vapor Retarder Placement Warm/humid climate “Smart” vapor retarder Perforated vinyl wall covering “The product is not suited for cooling climates with high outdoor humidities… Do not use with vinyl wall coverings or vapor retarding paints” - Manufacturer’s Literature Additional Considerations Vapor Diffusion Issues: Hot Climate Condensation on sheathing Vapor retarder on cold side of insulation Additional Considerations Vapor Diffusion Issues: Cold Climate Building Enclosure Fundamentals Summary Air barriers serve to reduce energy consumption and help mitigate moisture issues with the building envelope Continuity, integration, and compatibility are key to air barrier design, installation, and performance Performance of healthcare building enclosures are dependent on the performance of not only the air barrier, but also moisture barrier, thermal barrier, and vapor retarder Thermal barrier code changes as well as interior design conditions make healthcare facilities especially susceptible to increased risk of condensation Time for Questions and Comments Moderator John Kreidich McCarthy Building Cos