Rainscreen Cladding Systems

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

Transcript of Rainscreen Cladding Systems

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Central Artery/Tunnel Project - Ventilation Building No. 7 by TAMS/Wallace/Floyd Associates/Stull Associates

Rainscreen Cladding Systems Richard Keleher

Presentation Agenda


History● Historical projects● Local projects


Applications● Curtain wall details● Other Details

- What not to do- The window problem- Window details- Curtain wall details

● A case study project



Founder and Chair, BuildingEnclosure Council, Boston

Chair, AIA Building ScienceKnowledge CommunityAdvisory Group

Board Member, BETEC(Building Enclosure Technology &Environment Council)

Technical Quality & BuildingEnclosure Consultant

© Richard Keleher AIA CSI LEED

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Take-Away Messages1.



Cavity walls, or two-stage weather-tightening as it iscalled 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 oflate; hopefully this workshop will clarify what arainscreen is and how it may be used to advantageon your projects.


Causes ofDeterioration

• Ozone• Sunlight• Ultraviolet radiation• Rain• Snow• Temperature extremes• Differential thermal



• Proper surface preparation• Compatible sealant and• substrate• Proper backer rod type and

position• Properly tooled joints

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Sealant Geometry Requirements for Proper Performance

Forces Driving Air Through the Wall Air Pressure Differences

video clip 1 inch Video clip

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Air movement(not pressure-equalized)

No air movement(possibly pressure-equalized)

Pressuresat Corners

Weeped and Vented Pressure-EqualizedDrained and Vented

Note: block off excessive cavity sizeTypes of Rainscreens

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Pressure-Equalized (above)Non-Pressure-Equalized (below)

Pressure-Equalization Compartment Sizes

Asymmetrical venting: locate inletstoward center of façade to ensure complete pressure-equalization

• Rapid pressure-equalization and cavity-closers

• Air barrier versus vaporbarrier

• Adequate venting area

Air BarrierDesignRequirements

• Continuous

• Secure and rigid

• Air impermeable

• Durable

• A critical element forpressure-equalization

Principles ofPressureEqualization

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See next slide forrequired ventingarea.

The Four Planes(from outside to inside)

1. The Rainscreen2. The Drainage Plane3. The Air Barrier4. The Vapor Barrier

Rules of Thumb(with rigid air barriers andnon-gusting winds)

The air barrier shouldhave at least 10x the vaporpermeability of the vaporbarrier.

Leakage of the air barriershould not exceed 0.004cfm/ft2 under a pressuredifferential of 0.3 inches ofwater (1.56 psf)

Vent AreaThe greater of:

Static loads:Vent area ≥ 5 x ELA of the air barrier

plus 10 x ELA of any corner sealsplus 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 thenarrowest part of the venting path.

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Examples of Air Barriers

and insulation

Sealants not required

The air barrier is notsubject to:

Thermal movementHeavy wettingUltravioletradiation

Less condensation;cavity breathes anddries

Insulation on outer face ofinner leaf; not bridged bystructure

Complicated panelintersections are possible

Outer panel can be purelyesthetic; freedom from needto seal joints allows fordesign flexibility

Advantages of Rainscreens

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Concerns About RainscreensThe omission of sealant isn’t a panacea.

Fortunately,there isprogress on thelatter. AAMAhas a TaskGroup, ofwhich I am amember,working onsuch astandard.

Actually, if the joints in the rainscreen are leftunsealed, they can allow large amounts of waterinto the cavity, where they will be on an airbarrier (drainage plane) which now has the fullforce of the wind acting on it.

Lack of clarity about the responsibilityfor water penetration and lack of anational standard to prove performance.

There are many cases where the metal panelmanufacturer/ installer thinks that the air/vaporbarrier/ drainage plane installer is going to takecare of any water that gets past the metal panels.

Take-away MessageYou cannot reliably protect your building from water intrusionwithout using what the Europeans call “two-stage weather-tightening” and the Canadians call “rainscreen.” The Canadiansprefer to use the pressure-equalized variation of this wallconstruction, which they call “PERSIST,” or the Pressure-EqualizedRainscreen Insulated Structure Technique.”


An interior air-tight seal (the airbarrier)

An air chamber or vented cavity

A rain barrier, properly detailedto resist the Forces

ConcernsThe depth of knowledge of:

The A/EThe Contractor and Subs

Lack of national standardsInspection and testing

MockupsQuality control testingInspectionPost-construction testing

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History ofRainscreenCladding

Historical Sequence:Vapor Issues

• Historically, (several centuries ago and before) large-scale wallswere mass walls whose thermal mass delayed transmission oftemperature, absorbed water, and then dried-out (or in).

• To save energy, we added insulation which, in certain situationsled 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 vaporbehind the vapor barrier.

• Now, finally, we are addressing hygrothermal issues in walldesign , through the use of WUFI and other resources.

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• Skeletal frames led to the need for sealants, to seal thediscontinuous elements, which could not absorb the quantity ofmoisture that the monolithic bearing wall systems could.

• Difficulty of achieving an adequate and durable seal, evenwith high performance sealants. This defect was not realized forsome time

• Need for a predictable and durable method ofconstruction that was not subject to the need for perfectexecution and that would not be damaged by ultraviolet light.

• Development of the drained cavity wall (back-ventilated anddrained rainscreen) and then the pressure equalizedrainscreen.

Historical Sequence:Water Issues

Log House, Norway – centuries old “open-jointed barn” technique

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Sparrow House, Plymouth, MA, 1630 Shingles Brick Veneer Brick Veneer

After early work by the Scandinavians andCanadians (Kirby Garden et. al. at the NationalResearch Council/Canada – “The RainscreenPrinciple” published in 1965) and the adoption byAAMA of the rainscreen principle for curtainwalls shortly thereafter, the idea lay fallowexcept for an intuitive leap of faith by Harrisonand Abramovitz in their design of the AlcoaBuilding in 1971.

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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

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Royal Bank of Commerce Edmonton, Alberta, 1991

Calgary Oval Olympic Arena Roof

Xerox Corporation Mississauga, Ontario

Porcelain enamel panelson curve shed dirt

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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)

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Recently CompletedLocal ProjectsUtilizing theRainscreen Principle

(also, every curtain wall)




Federal Reserve Bank of Boston1975 The Stubbins Associates

Double-mullionunitized curtain wallwith 1/8” aluminumplate facing, clearanodized finish

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125 High Street Jung/Brannen Assoc. Dana-Farber Cancer Institute Smith Research Labs Shepley Bulfinch Richardson and Abbott

Unitizedcurtainwallswith stoneand metalpanelinfill panels

53 State Street WZMH Habib

53 State Street as anexample of a typicalpressure-equalizedcurtain wall system

Details on next slide

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Typical Spandrel SectionVent Holes in Horizontal Mullion

Alternate: IGU


The Stubbins Associates

back-ventilated and drained rainscreen

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Central Artery/TunnelBuildings Utilizing theRainscreen Principle








BigDig Administration Building Wallace, Floyd, Associates / Elkus Manfredi

BigDig Fire & Rescue Station Wallace, Floyd, Associates / Elkus Manfredi

This is the Case Study Building

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VentilationBuilding No. 5Wallace Floyd Design GroupCWA / MJA Joint Venture




air &vaporbarrier

Ventilation Building No. 6 Wallace Floyd Design Group / Barrientos Associates

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A message from our sponsorI am available for peer reviews and technical consulting in thefollowing phases:- General: office-wide drafting standards manual

- Schematic Design- Design Development- Construction Documents- Construction Administration- Best practices for high-performance sustainable design

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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

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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: reviewsets for:

– Coordination of drawings– Proper detailing of the

building enclosure


– Attend and advise onmock-up and field testing

– Resolution of unforeseenproblems

General:– Develop office-wide drafting

standards manual

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Construction Administration• Attend and advise on mock-up and field testing

General:• Develop office-wide drafting standards


• Studies of complex conditions• Resolution of unforeseen problems

State-of-the-Art Building Enclosures

• There is much that we have done, but we have muchmore 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 theirpractices (and their shirts)!

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ConclusionAssistance 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

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