A picture window is fixed, meaning it does not open or vent, and is designed to maximize natural light and offer an unobstructed view. This stationary design contributes to its energy efficiency, as there are no moving components that can compromise the air seal. Successfully installing a new picture window requires careful preparation and precise execution. This guide provides a step-by-step process for homeowners to complete a professional installation.
Planning and Preparation
The success of any window installation depends on the accuracy of the initial measurements taken on the rough opening. Measure the width of the framed opening at the top, middle, and bottom, using the smallest measurement as the determining width. Similarly, measure the height at the left, center, and right sides, noting the smallest figure to accommodate inconsistencies in the framing.
The rough opening must be slightly larger than the window unit to allow for shimming, leveling, and insulation. Industry standards recommend the rough opening be approximately $1/2$ inch larger than the window’s net frame size, providing a $1/4$ inch gap on all sides. Before removal, gather necessary materials, including shims, sealant, flashing tape, and safety gear. Check the existing rough opening for squareness and levelness to anticipate adjustments needed during installation.
Removing the Old Window
Begin the removal process by scoring the paint or caulk line where the interior trim meets the wall. Gently pry away the interior casing to access the fasteners holding the existing window frame. For older windows, remove the interior stops and carefully break out the glass or sash before tackling the main frame to reduce weight.
With the sash and interior trim removed, locate and cut or pull any nails or screws securing the old frame to the rough opening studs. Use a reciprocating saw or a pry bar to separate the frame from the surrounding wall structure. Once the unit is free, carefully lift it out of the opening, often requiring two people. Clear the rough opening of debris, loose nails, and old sealant to ensure a clean surface for the new installation.
Installation: Setting the New Frame
Apply a continuous bead of high-quality, exterior-grade sealant, such as polyurethane or silicone, along the back perimeter of the window’s nailing flange. This sealant acts as the primary moisture barrier between the frame and the house wrap or sheathing. Carefully lift the window and set it into the rough opening, centering the unit so the $1/4$ inch gap is distributed evenly around all sides.
Use shims to ensure the frame is level at the sill and plumb along the vertical sides. Place shims in pairs near the bottom corners, working inward, and near the head and side jambs, especially at fastening points. Once the window is level and plumb, secure the frame to the rough opening studs using manufacturer-recommended fasteners, starting at the top corners. Avoid over-tightening the fasteners, as excessive pressure can bow the frame, stressing the glass unit and compromising the thermal seal.
Continuously check the frame with a level and straight edge throughout the fastening process to confirm the frame remains square and true. Proper shimming and fastening prevent the transfer of structural loads from the house framing directly onto the window unit. Precise alignment is important for a picture window, as any distortion is visible across the large pane of glass. After the frame is fully secured, trim the shims flush with the frame.
Sealing and Trim Work
Weatherproofing the installation prevents water intrusion through flashing and insulation. Apply self-adhering flashing tape, often a butyl or asphalt-based product, over the nailing flange and onto the exterior wall sheathing using the “shingle style” principle. Apply the sill flashing first, followed by the vertical side pieces, and finally the top piece, ensuring each upper layer overlaps the layer below it to shed water downward.
Insulate the gap between the window frame and the rough opening studs to prevent air infiltration and thermal transfer. Use low-expansion polyurethane foam, which cures without exerting pressure that could distort the frame. This foam creates an effective air seal, superior to traditional fiberglass insulation.
The installation concludes with aesthetic finishing. Install exterior trim or casing to cover the flashing and frame edges. Apply a final bead of exterior-grade caulk to seal the trim against the siding and the window frame, avoiding any weep holes located on the bottom of the frame. On the interior, install the casing and sill trim to cover the shims and insulation, providing a professional, finished appearance.