For Designers

Apply Proper Window Details and Installation Practices

General Installation Guidelines Always follow manufacturer's instructions. Meet all codes regarding energy efficiency, structure, proper egress, safety glass, and grade (design pressure). Size the rough opening properly to accommodate thermal expansion and movement. Install the window unit level, plumb, and square. Maintain the continuity of the weather-resistant barrier. In a barrier system, this is achieved with sealants on the outermost surface of the wall. In a membrane/drainage system, residual water must drain freely on the drainage plane. Use flashings overlapped shingle style and drip caps where needed. Avoid trapping water within the wall. Do not leave thermal bridges between the interior and exterior. Carefully insulate all voids left between window and wall, but only use foam insulation that expands at a minimum rate. Maintain the integrity of air and vapor retarders. Avoid using incompatible materials such as certain metal combinations and only apply caulks and sealants that are compatible with the substrate.

No matter how advanced the glazing and frame materials may be in a window unit, the ultimate performance also depends on the quality of its installation. Improper installation can contribute to air leakage, unnecessary heat loss, condensation, and water leakage. This not only may lead to diminished energy performance but deterioration of walls, insulation, and the window unit itself.

Given the importance of proper installation, however, there are some emerging guidelines for installation. AAMA has developed an installer training and registration program and ASTM has developed a Window Installation Standard Practice. The EEBA Water Management Guide is another excellent resource.

Essentially, installing a window creates a break in several important aspects of the building envelope. A properly installed window must maintain barriers keeping air and water from penetrating the wall and it must restrict vapor flow. It must also reduce heat loss and condensation around the window unit. In addition, the installation must meet several structural and functional requirements. Building loads cannot rest on the window frame, the installation must allow for movement, the window must protect against forced entry, and yet it must maintain ease of operation.

The installation of a window and any treatments added to its exterior or interior can affect the energy efficiency of the total assembly, no matter how advanced the window unit. There are important differences in the details of how a window is installed, depending on the type of construction (wood versus masonry) or exterior cladding material (i.e., wood siding, stucco, brick veneer). In addition, each operator type, frame material, and individual manufacturer may have its own recommended installation practices. It is important to refer to the appropriate manufacturer's instructions and not to rely solely on general guidelines.