A three-step system for water management in scenarios where the window is replaced but the wall cladding is not
By Jim Katsaros and Alan Hubbell, DuPont Building Innovations
January 1, 2012
FEATURE ARTICLE | Operations, Methods & Techniques
Replacement windows and doors represent a sizable majority of the fenestration products installed into buildings in recent years, particularly with the drop in new construction starts and incentives provided for the energy efficient replacement units. While there has been significant effort in codes and standards to improve installation practices in new construction installations, relatively little effort has been expended in the replacement arena.

This is likely due to the high degree of variability in window/wall configurations and the complexity in robust integration to the building envelope when cladding is not removed. This article details a three-step approach to help align replacement window installations with the enhanced water management principles now specified for new construction systems.

Background
Starting with the formation of the ASTM E06.51.11 committee in 1995, there has been a significant effort focused on the development of industry standard practices for the installation of windows and doors into new construction residential buildings. The initial publication of ASTM E2112 Standard Practice for the Installation of Exterior Doors, Windows, and Skylights in 2001 was a landmark achievement in providing a comprehensive reference tool for fenestration manufacturers and installers. The principles behind ASTM E2112 were elegantly straightforward:

Select the right fenestration product for the task–including considerations such as exposure/climate/attachment
Prepare the rough opening to ensure the product will properly fit
Integrate the rough opening with the water resistive barrier (WRB), which provides air/water protection to the building envelope
Install the fenestration product into the rough opening, ensuring proper functioning (plumb/level/square and ensure proper operation)
Ensure complete integration between the fenestration product and the building envelope’s water-resistive barrier through correct lapping and sequencing of flashing and sealant materials
The 2007 revision to ASTM E2112 included more focus on drainage principles at the sill of the fenestration (i.e. sill pan systems) and proper integration with the membrane drainage plane.

While these principles may appear straight forward, the “devil is in the details.” Given the tremendous variation of fenestration attachment types, wall systems, and regional and environmental considerations, the generalized approach given by ASTM E2112 is limited in practical application. Therefore, a number of “regionally specific” installation practices have been developed. Examples include the FMA/AAMA/WDMA series for extreme wind and water exposure systems and the AAMA 2400 standard practice for open stud construction common to the southwestern U.S.

Furthermore, the 2009 version of the International Residential Code recognizes the importance of water managed installation practices, as stated for Flashing Exterior Walls as follows:

R703.8 Flashing. Approved corrosion-resistant flashing shall be applied shingle-fashion in such a manner to prevent entry of water into the wall cavity or penetration of water to the building structural framing components…
…Approved corrosion-resistant flashings shall be installed at all of the following locations:
1. Exterior window and door openings. Flashing at exterior window and door openings shall extend to the surface of the exterior wall finish or to the water-resistive barrier for subsequent drainage.

Thus, while a great deal of standardization effort has been applied to the installation of new construction residential windows and doors, there are no corresponding requirements, standard practices, or even industry recommendations for replacement window and door installations, which now represent over two thirds of all fenestration installations. Could this be explained by the fact that replacement windows and doors are less vulnerable to water intrusion damage than their new construction counterparts? We think not.

Fig. 1–Typical wall/WRB/cladding conditions that can be found when replacing windows.
In fact, in many ways the replacement systems are more vulnerable to water intrusion problems. This is due to the inherent settling and movement of the existing building leading to misaligned interfaces, which provides more opportunities for water entry and increasing difficulty to create water managed integrations. In addition, and most importantly, the existing façade, which is typically left in place, makes proper integration with the existing WRB highly challenging, if not impossible. Thus, to answer the question as to why replacement fenestration installations are not as regulated and standardized as new construction systems, it’s simply been considered too complex to follow the same water management principles as applied to new construction. However, this article will propose a general three-step method that can be applied to replacement fenestration systems that closely aligns with new construction water management principles.

Discussion
When considering replacement window and door installation practices, it becomes readily apparent that the new construction approach of providing prescriptive installation details would not be broadly applicable to this highly variable market space. The key challenge is the case where the existing cladding is not replaced, which represents the majority of replacement window installations, and integration with an acceptable water resistive drainage plane is not practical. If one cannot easily inspect the condition of the WRB (if it indeed exists) behind an existing façade, a reliable drainage plane cannot be assumed. In addition, integrating a replacement window into existing siding offers a wide range of possible configurations, including highly variable spacing around the rough opening, clearances between the cladding and the wall system. Fig. 1 provides an actual illustration of typical conditions that occur in window replacement systems, where integration with an ‘acceptable drainage plane’ behind the cladding is clearly not an option.

Cladding Replaced Cladding Not Replaced
Window Replaced Follow New Construction Guidelines Follow Three-Step Integration Method
Window Not Replaced General Inspection N/A
Table 1
The approaches for replacement window installation systems can thus be separated into a decision matrix format considering the state of window and cladding replacement. Table 1 illustrates these matrix options. The case of interest here is the windows replaced / cladding not replaced scenario, which is highly variable and complex depending on the nature of the existing cladding.

As such, the following water management installation principles are proposed to guide the “windows replaced/cladding not replaced” scenario:

Use a ‘drainable’ installation approach in order to manage water intrusion that occurs around the perimeter of the window-wall interface or through the joinery of the window framing system. A drainable installation features the use of a sill pan and/or sill pan flashing (such as DuPont FlexWrap NF), with an open path for drainage at the window sill to the exterior, along with an interior air and water barrier. Note: drainable installations are recommended for use under all window and door openings by ASTM E2112-07 (Section 5.16.3) and are required by the FMA/AAMA 100-07 standard practice for windows in wood frame construction in extreme wind/water exposure.
The drainable sill pan flashing system must be integrated with and drain onto an ‘acceptable drainage plane,’ In the case of new construction or complete cladding tear off system, a durable WRB (such as a DuPont Tyvek HomeWrap), integrated with the building envelope and rough opening serves this purpose.
When existing cladding is not replaced, it is impossible to determine whether an ‘acceptable drainage plane’ exists behind that cladding (see Figure 1). Therefore, drainage to the exterior must be provided by ‘through cavity’ flashing, thus directing water from the rough opening sill directly to the cladding exterior surface below the window.
In our assessment of the current replacement window installation techniques, it is clear that the Industry is not typically adhering to the water management installation principles described above. In fact, most replacement installations involve a full perimeter barrier sealant joint around the window frame inserted into either the existing window “cut out” or–by completely removing the ‘full frame’ of the existing window (“insert window” system)–into the existing rough opening. This ‘full barrier’ installation method, as specified in the ASTM E2112-01 first edition, can be problematic due to the high potential to trap moisture at the sill that enters through any place around or through the rough opening cavity–which is virtually inevitable during the life of a window installation. This results in an installation that is at risk of trapping moisture at the highly vulnerable (and hidden) corners at and below the sills of the windows–where most water damage behind the façade is found (see Figure 1).

Fig. 2–A method for connecting the sill flashing to a “through cavity” flashing component to drain water to the exterior.
In order to follow the water management principles defined above–in the windows replaced/cladding not replaced scenario–a system is proposed that features three key steps for replacement windows and doors:

Completely seal the rough opening (or existing window ‘cut out’) with a liquid-applied flashing material that meets the AAMA 714-11 specification. The liquid applied system has the ‘ultimate conformability’ to seal around any geometry and will act as the water managed ‘integration’ with the existing building envelope. Include drainable sill pan flashing, such that there are open paths for drainage below the sill of the window so moisture intrusion is not trapped.
Connect the sill flashing to a ‘through cavity’ flashing component that is sloped to the exterior and directed over the cavity between the frame and the exterior cladding. An illustration of the potential concept is illustrated below in Fig. 2. The key differential from existing sill pan systems is the drainage component of the flashing is directed to the exterior of the cladding, rather than behind the wall.
Apply a robust interior air/water seal through the use of sealant or low expansion foam around the entire interior perimeter of the window to prevent air/water intrusion to the building interior
These steps will better align the replacement window installation with the water management installation principles recognized for new construction systems and will go a long way to enhancing the moisture protection of the building envelope where replacement windows are installed.