FGIA InstallationMasters cheat sheet

Replacement work starts with a condition survey of the existing opening: check rough-opening dimensions at head, jamb, and sill; measure diagonals for square; and probe framing for rot, soft wood, or water staining before ordering product.

Removal rule: cut back interior and exterior sealant and trim first, then free the old unit from the rough opening. Never pry against finished interior walls; the new unit's dimensions are set from the actual rough opening, not from the old window's nominal size.

Fully framed replacement units (nail-fin or flush-fin) require removal of exterior siding or trim to expose the nailing flange; block-frame or pocket replacements fit inside the existing frame and are anchored through the jamb into the rough-opening framing.

Anchor spacing rule: fasteners at no more than 16 in (406 mm) on center along jambs and head, set 2-4 in (50-100 mm) from each corner, with fasteners driven perpendicular to the frame and shimmed so the frame is not distorted.

Level, plumb, and square are set with shims at sill, jambs, and head; measure both diagonals of the frame and equalize them before fastening. Operating force and sash alignment are checked after fastening, since over-driving anchors bows the frame.

Water management in replacement: sloped sill pan or back-dam at the sill, sill sealant under the sill flange, and a drainage path that lets water escape to the exterior. Sealant alone is not a substitute for flashing, and weeps must not be blocked by sealant or trim.

Air sealing sequence: low-expansion foam or backer plus sealant at the interior perimeter, continuous sealant at the exterior flange, and no gaps at the rough-opening corners. Use low-expansion foam only; high-expansion foam can bow jambs and jam operating sashes.

Flashing integration: head flashing or cap flashing laps over the upper flange, side flanges lap in shingle fashion (upper over lower), and the sill flange sits over the sill pan. Flashing tape joints must overlap at least 2 in (50 mm).

Final checks before sign-off: verify operation of all sashes and locks, confirm weeps are clear, inspect interior trim for square and tight joints, and confirm the unit is rated for the opening's exposure category and design pressure.

New construction begins with the rough opening: verify width and height against the manufacturer's rough-opening chart and check that the opening is square by comparing diagonals (difference of 1/4 in / 6 mm or less is generally acceptable).

Rough opening sizing formula: unit width plus 1/2 in (13 mm) total for a typical flange unit, but always use the manufacturer's published rough-opening dimensions; the rough opening must be larger than the unit to allow shimming and flashing.

Flashing sequence for a flanged unit in a framed wall: sill pan or sill flashing first, then the unit set and fastened, then jamb flashing tape, then head flashing tape, then the weather-resistive barrier (WRB) lapped over the head flange in shingle fashion.

WRB rule: the barrier is installed before the unit, lapped over the sill flashing, and the unit's flanges are integrated so that water drains to the exterior. Head flashing must lap over the side flashing, never under it.

Fastening: nail-fin units are fastened through the flange into framing with fasteners long enough to penetrate at least 1-1/2 in (38 mm) into solid wood, spaced per manufacturer's instructions (commonly 6-8 in / 150-200 mm at corners and 16 in / 406 mm along the perimeter).

Shimming and leveling: shims at the sill and at each jamb at hinge and lock points; check level, plumb, and square, and confirm the frame is not racked before final fastening. Remove excess shim material only after fasteners are set.

Installation types: flanged (nail-fin) units are used where the frame is exposed and flashing can be integrated; block-frame units are set into masonry or where a flanged unit cannot be flashed; the choice follows wall type and drainage path.

Sealant and air barrier: continuous sealant at the interior perimeter and at the exterior flange, with the air barrier of the wall tied to the unit's frame. Sealant joints should be sized for movement, not applied as a thin bead that will fail.

Inspection and testing: verify operation of sashes and hardware, check that weeps and drainage paths are clear, confirm the unit's performance rating (design pressure, water resistance) matches the project's exposure, and record the installation for the building envelope inspection.