Structural opening
Contents |
[edit] Use of the term
The term structural opening (SO), sometimes also called rough opening, refers to the size of an opening in a wall or facade where a window or door or other unit will be installed. It is normally slightly larger than the actual unit size to allow for tolerances in construction. Structural openings are called this such because their edges generally meet with structural elements of the building such as columns, walls, beams, lintels and so on.
[edit] Finished opening
The term finished opening (FO) is similar to structural opening in that it is the opening that will house a unit such as a window in a facade or wall. Although in this case the opening may have been prepared in some way rather than being a raw structural opening, for instance with fixing of plywood boxing, plaster or render between the structural element and the location of the window or other unit.
[edit] Tolerances
The width of a structural opening to the edge of brick and blockwork might be 910mm, the finished opening may have a lining of 10mm creating a finished opening that is 900mm wide, whilst the unit size that is intended to be installed is 890mm wide, leaving <5mm tolerance on all sides.
NHBC guidance 9.1.4 Doors and windows discusses appropriate tolerances of <3mm on one side to the other of an opening: "Doors and windows shall be installed to appropriate tolerances, including openings in walls and external openings viewed from the inside."
[edit] Thermal performance
It should be noted that a window or any unit installed into a structure can have an impact on fabric performance, as the opening punctuates the building fabric from inside to outside. Psi ( or ψ value) denotes heat loss over a given length rather than a given area. The thermal performance of a window should be calculated including an adjustment for the interface between the window unit and the structural or finished opening, this installation adjustment is often known as the window or installation Psi (ψw). It is an adjustment to the thermal performance of a window allowing for heat loss along the linear junction between the installed window and the edge of the opening.
[edit] Related articles on Designing Buildings
- Elements of structure in buildings
- Principles of enclosure.
- Structure.
- Structural systems.
- Superstructure.
- Types of structure.
- Types of door.
- Windows.
[edit] External references
Featured articles and news
We're expanding our collaborative mission by launching DB Intelligence, an exclusive market research advisory panel. Built environment professionals can now get paid to share their expertise on industry trends, products and services.
Panel members receive direct financial incentives for participating in research projects like short surveys, 1-2-1 interviews and focus groups. Register today to shape the future of the construction sector.
Building Control Independent Panel final report
A precis of a key report led by Dame Hackitt with full recommendations and link to the government response.
Guide to ISO 19650 for Architecture Firms (2026)
A user gives their low down.
A UK training and membership provider for mould remediation professionals.
Building Safety recap April, 2026
A short and longer run-through of the month, with links to further information and sources.
CIAT May 2026 briefing.
Independent NSI and BAFE study exploring how organisations are changing the way they buy fire safety services.
From medieval scribes to modern word art.
ECA welcomes crackdown on late payment and push for clean energy, whilst CIOB seek fixed cladding removal timeframes.
Cyber Security in the Built Environment
Protecting projects, data, and digital assets: A CIOB Academy TIS.
Managing competence in the built environment
ITFG publishes new industry guide on how to meet the ICC principles.
The UK's campaign to reduce noise pollution: Mythbusting, articles and topic guides.