Help Ensure Installed Performance
by Ken Brenden
Although doors and windows are susceptible to moisture
intrusion or excessive air infiltration, where leakage or draft problems
occur, they are not necessarily due to faulty window design. AAMA-certified
products that meet the code-mandated fenestration standard AAMA/WDMA/CSA
101/ I.S.2/A440-08 or its predecessors must pass various structural loading,
operating force, forced entry, water penetration and air leakage resistance
requirements in addition to numerous durability tests.
But these standards and tests do not account for the performance of the
window after installation —the source of most air leakage or water penetration
problems attributable to windows. While the former affects occupant comfort
and energy efficiency, the latter can lead to costly deterioration and
promote the growth of mold and mildew in wall cavities.
The Key is in the Barrier
The solution focuses on the integrity of the “drainage plane” of the exterior
wall. The drainage plane consists of a weather-resistant barrier (WRB)—often
composed of tar paper, but also felt, house wrap, etc.—installed behind
the exterior cladding and coupled with flashing. It provides a path for
moisture that penetrates the cladding system to move down and away from
the building. In all cases, the essential principle of window installation
is that the window units must work together with the exterior facing material,
sheathing and the WRB to form a fully integrated and effective drainage
plane. The proper use of flashing and sealants to seal the joints between
the rough opening and the window frame plays a key role in achieving this
The right sealant for a given application must meet several requirements.
It must provide a weather-tight seal that retains its integrity despite
thermal or seismic movement or structural forces due to wind load or settling.
It also must be capable of absorbing stress without transferring it to
the glass. Meanwhile, it must retain its properties while resisting the
effects of water and ultraviolet radiation over time. Consideration must
also be given to the type of surface to which the sealant must adhere
(a primer coat being necessary for some to ensure bonding), the configuration
of the joint to be sealed and the compatibility of the sealant with other
Critical performance characteristics of a sealant are its adhesive strength,
cohesive strength, recovery ability after deformation, tensile strength
and durability under the effects of weathering. The importance of adhesive
and cohesive strength is self-evident. Unless the sealant adheres securely
to the substrate, it will fail when subjected to tensile stress. Cohesive
strength is equally important, as a material that lacks the strength to
“hold itself together” cannot provide a suitable seal. Other attributes
include hardness, thin film integrity, elastic recovery, permanent set
and compression set, peel adhesion, yield strength, slump, sag, low-temperature
flexibility, ultraviolet resistance and water absorption.
Standards Can Guide the Way
Fortunately, guidance is available for the selection and application of
sealants, as well as for the proper design of the joints and glazing to
which the sealant is to be applied:
• AAMA 800-08, Voluntary Specifications and Test Methods for Sealants,
is a compilation of standards, specifications and test methods for determining
the performance of compounds, sealants and tapes.
• AAMA 812-04, Voluntary Practice for Assessment of Single Component Aerosol
Expanding Polyurethane Foams for Sealing Rough Openings of Fenestration
Installations provides test methods for determining the expansion properties
of the foam and allows the user to relate them to their probable effect
on fenestration framing.
• AAMA 850-91, Fenestration Sealants Guide Manual, is a guide for the
selection, use and application of sealants for factory or field glazing
as well as weather-seal applications.
In recognition of the difference between sealants used in the assembly
of doors and windows and those used in their installation, the March 2009
issue of the AAMA Verified Components List was the first to provide component
listings in two individual parts: Part One-Components of Certified
Windows and Doors; and Part Two-Materials and Components Used for Installation.
Ken Brenden serves as technical standards manager for the American
Architectural Manufacturers Association in Schaumburg, Ill. He may be
reached at firstname.lastname@example.org. His opinions are solely his own and do
not necessarily reflect those of this magazine.
© Copyright 2009 Key Communications Inc. All rights reserved.
No reproduction of any type without expressed written permission.