Design development is not a variation
Every drawing issued after contract adds detail. Some of that detail is the design being finished, and some of it is the design being changed, and the contractor is paid for only one.
QScope Team · 27 April 2026 · 5 min read
On a design and build contract the contractor prices the Employer’s Requirements and produces the Contractor’s Proposals. Design continues after contract, and drawings keep arriving for months.
The commercial question on every one of them is the same: is this the design being completed, or the design being changed?
Development is included
A contractor that priced a curtain walling system knew it would need detailed drawings, fixings, thermal breaks and interfaces. Producing them is design development. It was always going to happen, it was priced, and issuing the detail is not a variation.
The same applies where a specification says a system will achieve a performance standard. Working out how is the contractor’s job.
Change is not
If the Employer’s Requirements said one thing and the employer now wants another, that is a variation whatever it is called. Changing a floor finish, adding a room, moving a wall, upgrading a specification: all variations, all valued.
Where the arguments actually live
Ambiguity in the Employer’s Requirements. If the requirements are unclear, whose risk is the interpretation? Most design and build forms put the risk on the contractor, because it had the opportunity to qualify at tender and did not.
Divergence between requirements and proposals. Where the Contractor’s Proposals do not meet the Employer’s Requirements, the usual position is that the requirements prevail and correcting the proposals is not a variation.
Performance specifications. A requirement to achieve an acoustic or thermal standard puts the method on the contractor. If the method turns out to be more expensive than assumed, that is a pricing risk, not a change.
Statutory change is different
A change in the Building Regulations after contract that requires different construction is normally a relevant matter under most forms, and is treated as a variation. That is a specific provision rather than an application of the general test.
How to keep it manageable
- Register every drawing issued after contract, with a date and a note on whether it changes anything priced.
- Raise the question when the drawing arrives, not at the final account. A contractor that accepts thirty drawings in silence and challenges them a year later has a harder argument.
- Where it is a change, get an instruction. Without one there is no authority and no route into the account.
The honest position
Some of these are genuinely arguable and both parties can hold a reasonable view. The ones that are not arguable are the ones nobody raised at the time, and those are decided by the contract wording alone, which usually favours whoever drafted it.
QScope links every variation back to the instruction that authorised it, so a change with no instruction behind it is visible before the final account.