Rough opening vs frame size is one of the most important distinctions in a custom window order. The rough opening is the space prepared in the building for installation. Frame size describes the outside dimensions of the manufactured unit. Finished opening and visible glass size are different references again. Confusing these terms can produce a window that does not fit.

Name every dimension

Write the reference beside the measurement: structural opening, prepared opening, outer frame or visible glass. Include units and viewing direction. A drawing marked only 1500 by 1200 leaves the supplier to guess what those numbers describe and whether an installation allowance has already been applied.

For a replacement project, finishes may conceal the original opening. Identify what was actually measured and which parts remain uncertain. The installer can then determine whether further survey work is needed before final fabrication dimensions are approved.

Show the installation joint in section

The frame usually needs a designed relationship to the surrounding wall, including space for fixing, tolerances and perimeter sealing. The required detail depends on the system, substrate and project conditions. Do not apply the same automatic deduction to every window and door.

Ask the supplier and installer to show the agreed frame position and installation joint in a section. Identify which party determines the allowance and which party checks the prepared opening. The frame should not be made larger simply to cover an unresolved finishing problem.

Separate glass, frame and passage dimensions

A fixed window’s visible glass area is smaller than its outer frame. An opening sash has another set of clear dimensions once the frame, hardware and stops are considered. For serving windows or access openings, the usable clear opening may be the key requirement.

State both the overall available space and the required clear opening where relevant. The supplier can then propose a configuration and identify any conflict. An architect’s elevation showing a nominal opening does not automatically define the manufacturing size of every component.

Use a dimension-control schedule

• Opening identifier and location.
• Raw survey dimensions and measurement reference.
• Agreed installation detail and allowances.
• Final outer-frame dimensions.
• Required clear opening where applicable.
• Drawing revision and approving party.

Track revisions carefully. If a wall opening changes after approval, record the change and check whether the order has entered production. Avoid sending isolated dimensions by message without identifying which schedule they replace.

Review Shanghai Slang fixed windows and bifold windows in the window category. Label the dimension reference on the enquiry so the supplier can quote and draw the correct unit without assuming an allowance that the installer has not approved.