Record the appearance you want to retain
Before choosing a profile, note the window proportions, sash divisions, glazing bars, colour and relationship to the elevation. Flush or sliding-sash styles may fit, but no style is automatically right for a particular building. Compare samples and drawings with the existing appearance. Options depend on the opening and specification; confirm details rather than relying on a broad style label.
Check restrictions where they apply
Listed status, conservation-area controls, planning conditions or an Article 4 direction can affect what work is acceptable, but they do not apply identically to every address. Check with the relevant local authority whether your property and proposal are covered before committing to a design. If applicable, ask what information or consent is needed. In England, replacement glazing is subject to building regulations; that is separate from planning permission. Any lease or landlord conditions are separate again and should be checked with the responsible party.
Balance room use with a clear quotation
Choose opening positions with ventilation, furniture, cleaning access and handle reach in mind. Casements need outward clearance, while an inward tilt-and-turn needs space inside; a sash moves vertically. A repair may be suitable for a failed glass unit or hardware fault if the frame is sound, but inspection should establish this. Compare the proposed repair and replacement scopes, including measurements, frame and glass, finish, removal, access, installation and making good. Ask for exclusions and any provisional details in writing.