Three Steps to Integrating Replacement Windows and Doors into the Building Envelope

Although 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 more than two-thirds of all fenestration installations.

Is this because replacement windows and doors are less vulnerable to water intrusion damage than their new construction counterparts? We think not. The existing faade, which is typically left in place, makes proper integration with the existing water-resistant barrier (WRB) highly challenging, if not impossible.

Put simply, the reason replacement fenestration installations are not as regulated and standardized as new construction systems is because it is considered too complex to follow the same water-management principles as in new building. However, we propose a three-step method that can be applied to replacement fenestration systems and closely aligns with new construction water-management principles.

The challenge is when 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 faade, 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.

Where cladding remains intact, we propose the following water-management installation principles:

Use a drainable installation approach 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 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, a durable WRB integrated with the building envelope and rough opening serves this purpose.

In our assessment of the current replacement window installation techniques, it is clear the industry is not typically adhering to these principles. In fact, the vast majority of replacement installations involves a full-perimeter barrier sealant joint around the window frame inserted into either the existing window cutout 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.

Three-step Method

In order to follow the water-management principles defined above, we suggest three key steps for replacement windows and doors:

1. Completely seal the rough opening (or existing window cutout) with a liquid-applied flashing material that meets the AAMA 714-11, Voluntary Specification for Liquid Applied Flashing Used to Create a Water-Resistive Seal around Exterior Wall Openings in Buildings. 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 so there are open paths for drainage below the sill of the window and moisture is not trapped.

2. 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. The key difference 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.

3. Apply a robust interior air and water seal through the use of sealant or low-expansion foam around the entire interior perimeter of the window to prevent air and water intrusion to the building interior.

These steps will better align the replacement window installation with the water-management installation principles for new construction and will go a long way to improving the moisture protection of the building envelope when replacement windows are installed.

Alan Hubbell is residential marketing manager, DuPont Building Innovations; Jim Katsaros is the building envelope integration champion for DuPont Building Innovations.