1. Designing Cladding systems
Chapter 19
Designing Cladding systems

2. Primary Functions of Cladding
Keeping water out (gravity, wind driven/air pressure)
Preventing air leakage
Controlling the passage of light (especially sunlight)
Controlling the radiation of heat (maintain an acceptable interior surface temperature, comfortable for occupants)
Controlling the conduction of heat
Resist conduction of heat & cold
Avoid thermal bridges (EX metal studs exterior walls)
Controlling Sound

3. Secondary Functions of Cladding
Resisting Wind Forces
Controlling Water Vapor (retard passage)
Adjusting to Movement
Thermal expansion & contraction
Within the cladding system - temperature differentials inside & out
Between the cladding system & the structural frame
Moisture expansion & contraction
Structural movements (blg settlement,wind, quake, creep)
Resist Fire
Weather Gracefully (w/o streaking, oxidation, corrosion, freeze-thaw...)

4. Installation Requirements for Cladding
Should be easy to install
Attachment tolerances
Adequate dimensional clearances
Back-up / secondary systems

5. Conditions required for Water Penetration
1) Water must be present at the wall surface
The case in all except small buildings with overhangs
2) The cladding system must have an opening
Design without openings - Barrier Wall (difficult to achieve because)
Sealed Joints must be perfect - Precise & consistent field installation
Building movement tear or pull sealant loose
Sealant exposed to the destructive forces of the elements
Therefore the Design often has
Internal drainage and/or secondary lines of defense
Example - Brick cavity wall
3) A force must exist to move the water through the opening

6. Conceptual Approaches for Watertight Wall
Keep water away from the wall
Broad overhang (but still have wind driven rain)
Eliminate wall openings (Barrier wall)
Seal every seam and opening
Difficulties:
Sealant likely not perfectly installed
Sealant may fail over the life of the building
Remedies:
Internal drainage or secondary defense
Eliminate/neutralize the forces that move water

7. Forces Moving Water thru Cladding
Gravity
Momentum
Surface Tension
Capillary Action
Wind Currents

8. Gravity Problem: Solution:
The Forces of Gravity cause water to enter the cladding
Solution:
Slope joints/openings to the outside

9. Momentum Problem: Solution:
The momentum from rain falling at an angle carries the water into the cladding
Solution:
Joint cover
Labyrinth (maze)

10. Surface Tension Problem: Solution:
Water adheres to joint & is drawn into the cladding
Solution:
Drip groove

11. Capillary Action Problem: Solution: Water pulled into the cladding
Opening larger than a drop of water can bridge, or install a
Capillary break

12. Air Pressure Problem: Solution:
Differences in air pressure push, or pull water into cladding
Solution:
Pressure Equalization Chamber

13. Rainscreen Principle:
Wall
Rainscreen Principle:
Design the Cladding to
allow wind pressure
differences between
the outside and inside
to neutralized
themselves
pressure
Rainscreen
Rainscreen
Air Barrier
Pressure Equalization Chamber

14. Designed to Counteract Wind Forces
(Air Barrier)
PEC

15. Designed to Counteract the “Five” Forces
Gravity:
Sloped Sill
Momentum:
Upturned Interior Sill
Surface Tension &
Capillary:
Drip Grove
Wind:
Interior Weatherstripping

16. Sealant Joints Most cladding systems:
don’t exclusively use the rainscreen principle
Typically they incorporate sealants
Purpose - fill cladding joints to:
Prevent flow of air & water while:
Providing allowances for
installation tolerances
system movement

17. Sealant Materials Types: Gunnable & Solid Gunnable Sealant Materials
Viscous, sticky liquids (mastics) injected into joints
Applied with a caulking gun

18. Categories of Gunnable Sealants:
Low-range sealants - caulks
limited elongation
Uses: filling cracks & secondary joints (not cladding)
Medium-range sealants
Often butyl rubber or acrylic
elongation - 5 to 10%
Uses: seal “non-working joints (mechanically fastened)
High-range sealants
two part mixtures (polysulfides, polyurethanes, silcones)
elongations - 50% +/-
Uses: Working joints in cladding

19. Joint Design Joint too Narrow Joint too Deep Joint Correctly
Fails with movement
Joint too Deep
Sealant Wasted
Excess pressure on edges
Joint Correctly
Proportioned
Bond Breaker

20. Joint Design & Installation
Joint Cleaned
Install Primer: (Optional)
improves adhesion
Install Backup Rod
“fills” joint / support
spongy material
does not stick to sealant
Install Sealant
Tool Joint
Joint Sealant
Primer
Backer Rod

21. Solid Sealant Materials
Gaskets
Preformed Tape
Less sensitive to installation problems - Widely used

22. Curtainwall System
“an exterior cladding system supported at each story by steel or concrete frame, rather than bearing its own load to the foundations”
Therefore:
It can be thin and light regardless of its height

23. Curtainwall Testing Cladding System Mockup built & tested for:
Air infiltration test
Static water penetration test
Dynamic water penetration test
Structural performance under loading
Necessary changes (test failures) incorporated into the finalized design
Fabrication commences subsequent to testing

24. Cladding & Building Codes
Primarily Concerned with:
Structural Strength
Strength / stiffness, integrity of the system
Attachment to the building frame
Fire Resistance
Combustibility of the system
Design of parapets, spandrels
Firestops
Energy Efficiency
Thermal resistance, vapor retarder, air leakage

25. Sustainability Issues
Because of its effect on energy consumption, glass should be used in moderation.
Operable windows may reduce energy costs
Properly insulate opaque areas (& spandrels)
Eliminate thermal bridges
Design for air tightness
Consider (use) building orientation to reduce energy consumption
Consider photovoltaic cells