Record the operating style precisely
| Incoming style | Additional checks |
|---|---|
| Single- or double-hung | Sash proportions, meeting-rail height, balances, tilt clearance and actual operable opening. |
| Horizontal slider | Active panel, panel arrangement, track/sill support and clear opening with the sash open. |
| Casement | Hinge side, crank/handle position, screen location and outward swing clearance. |
| Awning / hopper | Hinge and opening direction, projection into the room or outside and operational clearance. |
| Picture / fixed | Frame profile, sightlines, glazing requirements, weight and support. |
| Tilt-turn or other specialized operation | Both operating modes, handle reach, interior swing and supplier-specific frame/anchor requirements. |
A change in style can change the frame profile and clear opening at the same ordered width and height. Check the new series rather than transferring assumptions from the old operator.
State the viewing direction
Draw a simple elevation and label VIEWED FROM EXTERIOR or VIEWED FROM INTERIOR. Mark hinges, active panels and sliding direction with plain-language notes. Then translate that sketch into the supplier’s handing convention.
OX/XO symbols and “left-hand” terminology are not safe without the manufacturer’s definition and viewpoint. Record “left panel moves right when viewed from outside” where that is the actual intent, and reconcile it with the quote.
Photograph obstacles: walls, faucets, counters, blinds, shutters, screens and exterior walkways. Demonstrate the intended opening motion during scope review. An operable sash that strikes a return is an installation-planning failure even when the frame fits.
Size the joined assembly
For two or more units, obtain the manufacturer’s overall assembly drawing. Confirm whether the windows are factory-mulled or field-mulled, the exact joining system, the total outside dimensions and any installation clearance required around that assembly.
Do not simply add catalog widths. Joining profiles, reinforcement, mull covers and receptors can alter the total. Conversely, some catalog assembly dimensions already include those components. Double-counting is another way to get the size wrong.
Record structural mull or anchor requirements, support beneath joints, total weight and the delivery path. A field mull may need access that a tight brick opening does not provide.
Coordinate the elevation
Review meeting rails, transom bars, sash proportions and glass sightlines across adjacent units. Equal overall heights do not guarantee equal daylight openings or aligned rails across different series.
Where the customer requests aligned tops or matching glass sizes, show the manufacturer’s elevation before release. Keep aesthetic coordination separate from measured fit; do not silently impose one opening’s dimensions on every window in a group.
Source notes
Manufacturer requirements apply only to the named products and applications. The field procedures and worked examples here are an educational synthesis.
- Andersen · Sizing guides and resources ↗
Product-specific sizing charts, opening information and technical documents.
- Pella · Vinyl technical planning documents ↗
Frame options and installation details, including block frames and brick-veneer applications.
- Simonton · Installation instruction library ↗
Separate regional and product installation documents, including replacement, coastal, garden and bay/bow applications.
- Marvin · Essential single-hung architectural details ↗
An example of manufacturer net-clear-opening dimensions for a particular product and configuration.