1. Define the building and scope
Start by deciding whether the project is a new building, a repair, a replacement or an addition. Each has different constraints. New work can coordinate openings and wall construction from the start. Renovation must respond to existing dimensions, reveals, historic joinery, finishes and the condition of the surrounding wall.
Record the building type, architectural character, age where known, current window form and project goals. Note which features must remain and which can change. Do not treat a photograph or product brochure as a site survey. Measure and assess the building with appropriately qualified people.
2. Map orientation, daylight and views
List each elevation and its orientation. Consider the path of direct sun, neighbouring buildings, trees, street views and the activities in each room. A south-facing room in one climate and context may need different shading from a sheltered north-facing space. Broad glazing can bring light and a view, but it can also create glare and reduce privacy.
Think about where light should reach, not only how much glass is proposed. A high opening can send daylight farther into a room; a low sill may improve a seated view but affect furniture and privacy. Review openings from inside and outside, at different times if possible. External shading is often more effective at controlling direct sun than relying only on interior coverings, but suitability depends on the design.
3. Set ventilation and opening needs
Separate ventilation from the desire for a wide opening. A room may need routine background ventilation, purge ventilation, or both, depending on its use and the building strategy. Fixed glazing provides no opening ventilation. Casements, sliding units, tilt operations and other arrangements provide different opening patterns and clearances.
Make an operation schedule: identify which windows need to open, how often, who will operate them and whether access is safe. Check furniture, curtains, screens, wind exposure and cleaning. A large operable sash may need more clearance and effort than a modest one. Confirm ventilation provisions and applicable rules with a qualified professional.
4. Balance privacy with daylight
Map sightlines from public paths, neighbouring windows and shared spaces. Options can include sill height, opening position, divided or obscured glazing, planting, external shutters and interior screening. Each changes the view or daylight differently. A privacy solution should be considered alongside the façade, not applied as a last-minute film or blind choice.
For bedrooms and bathrooms, consider the view at night as well as daytime. Exterior darkness does not guarantee privacy when interior lighting is on. Confirm the appearance of any privacy glazing and how it affects the room's outlook before specifying it.
5. Choose frame depth and material
Frame depth affects sightlines, reveal proportions and the transition between window and wall. Compare the visible frame from both sides. A deep reveal can create shade and shadow; a frame set close to the outer face can produce a different façade expression. Wall build-up, insulation, cladding and existing masonry constrain placement.
Choose material by appearance, maintenance plan, repairability, exposure and compatibility with the building. Timber, aluminium, timber-aluminium, steel and composite systems each have variations. Ask for exact drawings and surface samples. No material category alone establishes durability, thermal performance or suitability.
6. Select glazing by use and exposure
Glazing decisions involve daylight, solar control, privacy, safety, noise and thermal requirements. The correct combination depends on location, building use, orientation and applicable standards. Do not infer acoustic or thermal performance from glass appearance or pane count. Ask for project-specific documentation and professional review of the complete window assembly.
Consider reflections and colour from both interior and exterior viewpoints. Large panes may need safety consideration in locations where impact is possible. Review cleaning access, replacement logistics and shading. If a project has specific acoustic, security or conservation demands, state them early and have the design team assess suitable options.
7. Match opening type to room use
Use casements where a hinged opening and its clearances suit the room. Consider sliding systems where a swinging sash would conflict with circulation or furniture. Sash windows can preserve a vertical façade rhythm and provide a familiar operating pattern. Fixed panes may be appropriate for view and daylight where opening is not required.
Check handle reach, safe access, insect screens, child safety where relevant, and the position of furniture. For upper floors or roof openings, professional review of safe operation and cleaning is essential. Operation should be tested against everyday routines, not chosen from elevation drawings alone.
8. Plan for maintenance and renovation
Every frame and finish needs a care plan. Consider exposure, access, repainting or cleaning, hardware checks, seal condition and the availability of repair. A low-maintenance intention is not the same as no maintenance. Ask what can be repaired independently and what requires specialist service.
For replacement, inspect the wall and reveal for moisture damage, movement, old fixings and previous alterations. Confirm whether internal trim, external render or sill work will be disturbed. Existing openings can impose limits on frame depth and visible profile. Check planning, heritage and building requirements before removal or alteration.
Practical selection framework
Rank each priority as essential, preferred or flexible: architectural match; daylight; view; privacy; ventilation; solar control; accessible operation; maintenance; and budget, where project costs are being assessed by the project team. Eliminate options that fail essential constraints. Compare the remaining systems in elevation, section and finish sample—not by product name alone.
Good for: preparing a clear brief for an architect, conservation professional, energy adviser or window specialist.
What to know: this framework is informational. It does not replace architectural, structural, energy, safety or building-regulation advice. Structural design and installation details must be reviewed by qualified professionals for the project.
Specification notes
Keep a schedule for every opening: room, elevation, orientation, dimensions, operation, frame material and finish, glazing requirements, shading, privacy, ventilation, access and renovation constraints. Record unknowns as questions instead of assuming answers. Request coordinated drawings and documentation for the exact proposed assembly before approval.