Installation · 6 min read
What Does a Good Window Survey Actually Include?
A good survey turns design intent and provisional dimensions into a coordinated, manufacturable installation plan.
Who Is Responsible If the Window Opening Sizes Are Wrong?
It depends on who measured and who issued the manufacturing dimensions. The way to avoid the argument is to make that explicit in writing before anything is made.
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: if the glazing supplier surveyed the building and issued the manufacturing sizes, responsibility for those sizes normally sits with them. If the builder or designer issued sizes and the supplier manufactured to them, it usually sits the other way. Problems arise when nobody can say which happened.
This is general guidance about how these projects are usually arranged. It is not legal advice, and liability in any particular case depends on the contract between the parties.
The common arrangements
| Arrangement | Who measures | Who normally carries the risk |
|---|---|---|
| Supplier surveys after order | Glazing supplier | The supplier, for the dimensions they issued |
| Manufactured to builder's sizes | Builder | The builder, for the sizes supplied |
| Manufactured to drawing sizes without survey | Designer's drawings | Whoever confirmed the drawings were survey-accurate |
| Opening built after units are made | Builder works to given sizes | The builder, if the opening does not match |
| Opening altered after survey | Changed by others | Whoever made the change without notifying |
How we remove the ambiguity
- 01Quotation stageSizes are taken from drawings or preliminary measurements and identified as provisional.
- 02After orderWe carry out the detailed survey of the actual building.
- 03ConfirmationFinal manufacturing information is issued and confirmed with you before anything is made.
- 04Changes after that pointAny alteration to the opening after confirmation has to come back to us, because the units are already in manufacture.
New builds and extensions are the higher-risk case
On a new build or extension, the opening often does not exist when the order is placed. Either the units are made to a designed size and the builder must build to it, or manufacture waits until the opening is formed and surveyed. Both are workable; what causes disputes is starting down one route and switching to the other. Agree which it is, in writing, with the builder present.
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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