Installation · 3 min read
When Should I Speak to a Glazing Company?
Earlier than most people do. A conversation at drawing stage costs nothing and routinely prevents changes that cost thousands once the building is underway.
When Should I Choose Windows During an Extension?
At design stage, before structural openings are finalised. Once the steel is designed and the blockwork is up, the glazing has to fit what exists rather than what you wanted.
3 min read
Written by Windows in the Lakes · A trading name of Home Glazing Ltd · Last reviewed 21 September 2026
Short answer
In short: choose the glazing while the drawings are still being developed. Structural openings, cill heights, thresholds and the position of supports all depend on what you intend to install, and all of them become expensive to change once they are built.
What depends on the glazing decision
| Decision | Fixed by | Cost of changing afterwards |
|---|---|---|
| Structural opening width | Steel design | High — new structural design and works |
| Head height and ceiling line | Structure and roof build-up | High |
| Level threshold and drainage | Floor slab and external levels | High — slab levels are difficult to revisit |
| Door type and stacking direction | Opening width and internal layout | Moderate |
| Glass specification | Order date | Low if caught before manufacture |
| Frame colour | Order date | Low |
Thresholds are the classic late discovery
A level threshold has to be planned into the slab, the insulation, the external drainage and the finished landscaping. It cannot be added at the end. If a flush transition to the garden matters to you, that has to be stated before the floor is poured.
A practical sequence
- 01ConceptAgree where glass goes and roughly what type — sliding, bifolding, fixed, rooflight.
- 02PlanningOpenings and appearance are fixed in the application drawings; changing them later can require an amendment.
- 03Technical designWe review sizes, thresholds, structural openings and interfaces with the builder and designer.
- 04QuotationA clear, itemised quotation based on the developed design.
- 05Order and detailed surveyAfter order, we survey the actual structure and confirm final manufacturing information before anything is made.
Sources and further reading
Regulatory and technical points in this guide should be checked against the current published guidance below, and against the specific circumstances of your property.
Guidance last reviewed 21 September 2026 by Windows in the Lakes
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