Windows are one of the most vulnerable areas of the wall system. Along with selecting high-quality products, proper window installation is crucial. Making mistakes with sizing, neglecting proper sealing or fastening, or failing to align units properly can affect how the window operates, whether it is weather-tight, and how long it lasts.

The first step to proper window installation is to follow all manufacturer instructions. Most window installations are the same, but each company may have its own specific requirements due to design, material, and other factors. To ensure proper performance and preserve the warranty, review and follow the specific instructions provided with the windows.

In addition to the window installation instructions, here are a few best practices:

  1. Handle with care. Keep the window closed when carrying it around the jobsite—resist the urge to carry it by an open sash, which can dislodge the balancer. Place and install the window in the closed and locked position.
  2. Size the window properly. Windows need to be approximately ½” smaller than the opening to accommodate expansion as well as imperfect openings.
  3. Follow fastener guides. Each window has been tested with a certain fastener schedule; Westlake Royal windows, for example, are tested and designed with a fastener installed every 12” o.c. Our nailing fins have pre-punched holes about 4” apart, so fastening every other hole will keep you within the 12”. We also require fasteners within 2” of each corner in order to achieve maximum performance.
  4. Consider your region. Window performance relies on specifying the right window for the conditions. Coastal areas, for example, will require a higher DP rating and stronger glass to ensure integrity, longevity, and expected performance.
  5. Accommodate for expansion and contraction. Like most building materials, windows are likely to expand and contract with temperature swings. On the exterior, we recommend using a 3/16” barrier for a caulk joint. A backer rod can be used for a larger gaps.
  6. Seal the nail flange. Before setting the window, apply a 3/8”-diameter bead of sealant to the back side of the nailing flange. Leave the bottom open for drainage.
  7. Operate the window. Window openings are rarely perfect, so when setting the window into the opening, ensure it’s plumb, level, square, and true, using shims when necessary; tack the window in place with a couple of nails, then open, close, and lock the window to ensure proper operation and good margins around the sash. Once the window is perfectly aligned and shims are placed, proceed with the full fastener schedule.
  8. Ensure flashing tape is AAMA approved.

Once the window is fastened into the hole, it will be difficult to maneuver the unit to add a shim or make other adjustments. Therefore, installation is the time to correct any issues with the window, so use care and take the necessary time to get it right.

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