rain-theory-handout

1 Central Artery/Tunnel Project - Ventilation Building No. 7 by TAMS/Wallace/Floyd Associates/Stull Associates Rainscreen Cladding Systems Richard Keleher Presentation Agenda Principles History ● Historical projects ● Local projects Video Applications ● Curtain wall details ● Other Details - What not to do - The window problem - Window details - Curtain wall details ● A case study project Summary Presenter: Founder and Chair, Building Enclosure Council, Boston Chair, AIA Building Science Knowledge Community Advisory Group Board Member, BETEC (Building Enclosure Technology & Environment Council) Technical Quality & Building Enclosure Consultant © Richard Keleher AIA CSI LEED 2 Take-Away Messages 1. 2. 3. Cavity walls, or two-stage weather-tightening as it is called in Europe, are the only way to obtain durable, dependable weather-tightness. The importance of the air barrier to prevention of: ● Water penetration (performance of rainscreens) ● Mold, mildew, rot, and corrosion. Canadians: “cherchez le trou,” or “find the hole.” The term “rainscreen” has been bandied-about of late; hopefully this workshop will clarify what a rainscreen is and how it may be used to advantage on your projects. Sealants Causes of Deterioration • Ozone • Sunlight • Ultraviolet radiation • Rain • Snow • Temperature extremes • Differential thermal movement Installation Requirements • Proper surface preparation • Compatible sealant and • substrate • Proper backer rod type and position • Properly tooled joints 3 Sealant Geometry Requirements for Proper Performance Forces Driving Air Through the Wall Air Pressure Differences video clip 1 inch Video clip 4 Air movement (not pressure-equalized) No air movement (possibly pressure-equalized) Pressures at Corners Weeped and Vented Pressure-EqualizedDrained and Vented Note: block off excessive cavity sizeTypes of Rainscreens 5 Pressure-Equalized (above) Non-Pressure-Equalized (below) Pressure-Equalization Compartment Sizes Asymmetrical venting: locate inlets toward center of façade to ensure complete pressure-equalization • Rapid pressure- equalization and cavity- closers • Air barrier versus vapor barrier • Adequate venting area Air Barrier Design Requirements • Continuous • Secure and rigid • Air impermeable • Durable • A critical element for pressure-equalization Principles of Pressure Equalization 6 See next slide for required venting area. The Four Planes (from outside to inside) 1. The Rainscreen 2. The Drainage Plane 3. The Air Barrier 4. The Vapor Barrier Rules of Thumb (with rigid air barriers and non-gusting winds) The air barrier should have at least 10x the vapor permeability of the vapor barrier. Leakage of the air barrier should not exceed 0.004 cfm/ft2 under a pressure differential of 0.3 inches of water (1.56 psf) Vent Area The greater of: Static loads: Vent area ≥ 5 x ELA of the air barrier plus 10 x ELA of any corner seals plus 1 x ELA of intermediate compartment seals ELA = Effective Leakage Area Dynamic loads: Vent area (m2) ≥ volume of compartment (m3)/ 50m Note: The Effective Vent Area is limited to by the narrowest part of the venting path. 7 Examples of Air Barriers and insulation Sealants not required The air barrier is not subject to: Thermal movement Heavy wetting Ultraviolet radiation Less condensation; cavity breathes and dries Insulation on outer face of inner leaf; not bridged by structure Complicated panel intersections are possible Outer panel can be purely esthetic; freedom from need to seal joints allows for design flexibility Advantages of Rainscreens 8 Concerns About Rainscreens The omission of sealant isn’t a panacea. Fortunately, there is progress on the latter. AAMA has a Task Group, of which I am a member, working on such a standard. Actually, if the joints in the rainscreen are left unsealed, they can allow large amounts of water into the cavity, where they will be on an air barrier (drainage plane) which now has the full force of the wind acting on it. Lack of clarity about the responsibility for water penetration and lack of a national standard to prove performance. There are many cases where the metal panel manufacturer/ installer thinks that the air/vapor barrier/ drainage plane installer is going to take care of any water that gets past the metal panels. Take-away Message You cannot reliably protect your building from water intrusion without using what the Europeans call “two-stage weather- tightening” and the Canadians call “rainscreen.” The Canadians prefer to use the pressure-equalized variation of this wall construction, which they call “PERSIST,” or the Pressure-Equalized Rainscreen Insulated Structure Technique.” Summary Essentials An interior air-tight seal (the air barrier) An air chamber or vented cavity A rain barrier, properly detailed to resist the Forces Concerns The depth of knowledge of: The A/E The Contractor and Subs Lack of national standards Inspection and testing Mockups Quality control testing Inspection Post-construction testing 9 History of Rainscreen Cladding Historical Sequence: Vapor Issues • Historically, (several centuries ago and before) large-scale walls were mass walls whose thermal mass delayed transmission of temperature, absorbed water, and then dried-out (or in). • To save energy, we added insulation which, in certain situations led to severe vapor deposition. • To prevent this, we added vapor barriers, but in so doing, prevented the drying of walls inward. • And often we still had air leakage, which transported vapor behind the vapor barrier. • Now, finally, we are addressing hygrothermal issues in wall design , through the use of WUFI and other resources. 10 • Skeletal frames led to the need for sealants, to seal the discontinuous elements, which could not absorb the quantity of moisture that the monolithic bearing wall systems could. • Difficulty of achieving an adequate and durable seal, even with high performance sealants. This defect was not realized for some time • Need for a predictable and durable method of construction that was not subject to the need for perfect execution and that would not be damaged by ultraviolet light. • Development of the drained cavity wall (back-ventilated and drained rainscreen) and then the pressure equalized rainscreen. Historical Sequence: Water Issues Log House, Norway – centuries old “open-jointed barn” technique 11 Sparrow House, Plymouth, MA, 1630 Shingles Brick Veneer Brick Veneer After early work by the Scandinavians and Canadians (Kirby Garden et. al. at the National Research Council/Canada – “The Rainscreen Principle” published in 1965) and the adoption by AAMA of the rainscreen principle for curtain walls shortly thereafter, the idea lay fallow except for an intuitive leap of faith by Harrison and Abramovitz in their design of the Alcoa Building in 1971. 12 Alcoa Building Pittsburg, PA, 1952 - Harrison & Abramovitz Interior plaster finish served as the air barrier. Tested in 1971 by AAMA - perfectly weather- tight. National Aviation Museum Ottawa, Ontario, 1986 Architect: Parkins & Associates Aluminum Plate Rainscreen (pressure-equalized) by Vicwest Steel 13 Royal Bank of Commerce Edmonton, Alberta, 1991 Calgary Oval Olympic Arena Roof Xerox Corporation Mississauga, Ontario Porcelain enamel panels on curve shed dirt 14 Terra Cotta Rainscreen (back-ventilated and drained) by Shildan (MBK, Terreal) East Boston Savings BankSystem Diagram Carwill House Vermont William Pederson Wood Siding Rainscreen (back-ventilated and drained) 15 Recently Completed Local Projects Utilizing the Rainscreen Principle (also, every curtain wall) AMGEN CAMBRIDGE ◄ DANA-FARBER LABS N.E. DEACONESS ◄ FEDERAL RESERVE BANK OF BOSTON Federal Reserve Bank of Boston 1975 The Stubbins Associates Double-mullion unitized curtain wall with 1/8” aluminum plate facing, clear anodized finish 16 125 High Street Jung/Brannen Assoc. Dana-Farber Cancer Institute Smith Research Labs Shepley Bulfinch Richardson and Abbott Unitized curtain walls with stone and metal panel infill panels 53 State Street WZMH Habib 53 State Street as an example of a typical pressure-equalized curtain wall system Details on next slide 17 Typical Spandrel SectionVent Holes in Horizontal Mullion Alternate: IGU Amgen The Stubbins Associates back-ventilated and drained rainscreen 18 Central Artery/Tunnel Buildings Utilizing the Rainscreen Principle VENTILATION BUILDING NO.4 VENTILATION BUILDING NO.6 VENTILATION BUILDING NO.5 VENTILATION BUILDING NO.1 VENTILATION BUILDING NO.7 OPERATIONS AND CONTROL CENTER TOLL PLAZA ADMINISTRATION BUILDING BigDig Administration Building Wallace, Floyd, Associates / Elkus Manfredi BigDig Fire & Rescue Station Wallace, Floyd, Associates / Elkus Manfredi This is the Case Study Building 19 Ventilation Building No. 5 Wallace Floyd Design Group CWA / MJA Joint Venture Back-ventilated rainscreen Air (vent) Rigid insulation air & vapor barrier Ventilation Building No. 6 Wallace Floyd Design Group / Barrientos Associates 20 A message from our sponsor I am available for peer reviews and technical consulting in the following phases: - General: office-wide drafting standards manual - Schematic Design - Design Development - Construction Documents - Construction Administration - Best practices for high-performance sustainable design 21 Schematic Design • Recommended Systems • Review SD Set - Uniformat Outline Specifications for building enclosure - Constructability, sequencing and relative costs - Typical large-scale details that are actually correct! less zooming • Climate Data Analysis Schematic Design continued - Comparisons to MA weather - Comparisons to the comfort zone - Wind roses 22 Design Development • Architectural Sheet List • Cartoon Set Covey • Typical Wall Sections • Project-specific Typical Details • Complex Details (e.g. seismic joints) • Review DD Set Construction Documents, CA, etc. Construction Documents: review sets for: – Coordination of drawings – Proper detailing of the building enclosure Construction Administration: – Attend and advise on mock-up and field testing – Resolution of unforeseen problems General: – Develop office-wide drafting standards manual 23 Construction Administration • Attend and advise on mock-up and field testing General: • Develop office-wide drafting standards manual • Studies of complex conditions • Resolution of unforeseen problems State-of-the-Art Building Enclosures • There is much that we have done, but we have much more to go! • Air barriers will be adopted nationally. Issues: – Implementation. – Air pressures. • Balancing. • Leaks/condensation. – Over-design of mechanical systems. • Architects need to take the initiative to save their practices (and their shirts)! 24 Conclusion Assistance in best practices for: • High-performance • Sustainabililty • Durability • Creativity! Herb Garden on Vancouver's Fairmount Waterfront Hotel (courtesy David Walker) Ventilation Building No.7 TAMS/Wallace Floyd Design Group / Stull & Lee Video Provided by Centria 25