A change log in a Bill of Quantities is a running register of every post-contract change that affects scope, quantity, cost or time, with the instruction behind it, the valuation and its status. On most UK projects it is the variation register. On higher-risk buildings in England there is also a statutory change control log, which is a separate document with its own legal content. This guide covers both, and shows how to build a log that makes the final account a calculation rather than an argument.
TL;DR
- A BoQ change log records each change against the priced BoQ baseline: what was instructed, by whom, what it does to quantities, and how it is valued.
- RICS guidance on change control treats the register as a tool for protecting the project baseline, and it should be kept current rather than rebuilt at final account.
- Not every change is a variation, and an error in the BoQ is not the same thing as a design change. The log should separate them.
- On higher-risk buildings in England, the principal contractor must keep a statutory change control log under Part 3 of the 2023 Regulations. A commercial variation register does not replace it.
Table of Contents
- What a BoQ change log is for
- What to record for each change
- Valuing each change against the BoQ
- BoQ errors versus variations
- Keeping the log current
- Higher-risk buildings in England: the statutory change control log
- Spreadsheet or software?
- Where QuantiFlow fits
- FAQ
- Sources
What a BoQ change log is for
The priced BoQ is the baseline. Every later change is measured against it, so the log is only as useful as its link back to the BoQ items it touches.
RICS describes change management as the skills, tools and techniques that let changes be carried out effectively at both pre- and post-contract stages (see Change control and management). The practical point for a quantity surveyor is simple. If instructions, quotations and drawing revisions sit in separate inboxes, nobody can say what the contract sum has become. The log is the one place where that answer lives.
The same RICS document warns about scope creep: small additions that are never recorded quietly breach the original cost and time limits, and the final account then becomes a point of contention. A log kept as you go is the cheapest defence against that.
Variation register, change log, change control log
The terms overlap, and it helps to be exact about which you mean.
| Term | Where it applies | Nature |
|---|---|---|
| Variation register or change log | Any project, any contract | Commercial and contractual record. Kept as good practice and to support the final account |
| Change control log | Higher-risk buildings in England | Statutory record kept by the principal or sole contractor for each controlled change |
| Drawing revision register | Design team and QS | Tracks which drawing issue each document or quantity is based on |
These three records should refer to one another, but they answer different questions and are usually held by different people.
What to record for each change
A useful log has one row per change, and every row can be defended from the file. The research behind RICS guidance points to a register that includes the formal instruction, the legal basis, a breakdown of labour, material and plant, and the status of the change (agreed, rejected or under consideration). A working layout built on that looks like this.
- Reference number. Sequential and never reused, even when a change is withdrawn.
- Date raised and date instructed. These are often different, and the gap matters for time and cost.
- Source of the change. Architect's instruction, employer's instruction, contractor proposal, site condition or a drawing revision.
- Contractual basis. The clause or mechanism under which the change is instructed or valued. Check this against the contract in front of you, not against a template.
- Description. Enough to identify the work without opening the attachment.
- BoQ items affected. Item references from the bill, with the measured quantity before and after.
- Drawing and specification references. Include the revision letter or number on both sides of the change.
- Valuation method. BoQ rate, pro rata rate, daywork or a new rate. See the next section.
- Cost and time effect. Cost, with the breakdown behind it, and any extension of time claimed or granted.
- Status. Under consideration, agreed, rejected or withdrawn, with the date of each status change.
- Author and checker. Who entered it and who reviewed it.
The status column does more work than it looks. Keeping rejected and withdrawn items visible stops the same item being re-priced three months later by someone who never saw the earlier decision.
Cost-bearing and non-cost-bearing changes
A common misconception, noted in the same RICS guidance, is that every change adds cost or time. Some instructions are administrative, such as clarifications, and carry no financial effect. Log them anyway, with a clear "no cost or time effect" flag. A rigorous log distinguishes the two, which prevents disputes over what was never claimed in the first place.
Valuing each change against the BoQ
The BoQ rates are the starting point for valuation. According to RICS NRM2, a variation is valued by direct use of BoQ rates for similar work. Where no applicable rate exists, a new priced item is compiled in line with the contract's measurement rules. Your log should state which route you took for each row, so the reviewer can see why.
How far a rate can be stretched to cover work that is not quite the same depends on the contract form. RICS has published Valuing change, a practice information document that summarises how change is valued under JCT, NEC and FIDIC. Read the clause for your form before you rely on a general rule.
Worked example of a log entry
Take an invented instruction to change the specification of an internal partition. The figures are illustrative only.
- Ref: V014
- Source: Architect's instruction, drawing revision C replaces revision B
- BoQ items affected: two partition items, plus linked finishes
- Quantity change: measured area omitted from one item, a different area added to a new item
- Valuation: omission at the BoQ rate. Addition at a new rate, because the revised build-up is not similar to any billed item
- Status: under consideration, awaiting the contractor's quotation
The value of that row is not the arithmetic. It is that someone who joins the project later can follow every step from the instruction to the number.
BoQ errors versus variations
This is the distinction that separates a careful log from a tidy one. An error in the BoQ is not automatically a design change.
Per the NRM2 guidance, under many contracts the employer carries the risk for the accuracy of the BoQ. If quantities were measured inaccurately against the measurement rules, the correction is typically treated as a variation, and the BoQ rates are used to re-value the work. The contract wording decides, so check the clause on inaccurate quantities before you decide how to label the row.
In the log, give errors their own source category rather than mixing them with design changes. That makes it much easier to answer later questions: how many changes came from design development, and how many from corrections to the bill. For how the bill sits within the contract, see our guide on how construction contracts use BoQ.
Keeping the log current
The log is a working document, and the reconciliation at the end is only as good as the habit during the job.
- Update on a set rhythm. The RICS change control guidance points to updating the register at least monthly, so that instructions, substantiation and cost effects are captured before the final account is reconciled.
- Standardise submissions. If contractors send variations in different formats, assessing each one takes longer and is more likely to be disputed. A single template with the fields above fixes most of this.
- Tie each row to a drawing revision. Most disputed quantities trace back to someone measuring from the wrong issue. Our notes on drawing revision control for QS teams cover that workflow.
- Re-measure the affected items only after the revision is confirmed. The steps are in our article on how to remeasure after revisions.
- Do not delete. Supersede, mark rejected or mark withdrawn. The history is the evidence.
Tender-stage changes
Changes do not start at contract award. Addenda during tender alter quantities too, and a clear record at that stage gives the post-contract log a clean opening position. See our seven-step triage for tender addendum quantities. The bill itself also evolves from the cost plan, as covered in how cost plans evolve to BoQ.
Higher-risk buildings in England: the statutory change control log
If the project is a higher-risk building in England, there is a legal requirement on top of good practice. Regulation 18 in Part 3 of The Building (Higher-Risk Buildings Procedures) (England) Regulations 2023 applies when a "controlled change" is proposed, which includes a change to current plans of the work or to the way work is carried out.
The principal or sole contractor must keep the log. For each controlled change it must record:
- the name of the person recording the change
- a description of the change and the reasons for it
- its classification: recordable, notifiable or major
- any advice sought
- an explanation of how the change complies with the regulations
Notifiable and major changes need the Building Safety Regulator involved before work proceeds. The GOV.UK guidance on making changes to a higher-risk building project, last updated 27 March 2025, explains that the documents uploaded with the building control application are the "agreed documents", and any change to them is a controlled change. The same guidance describes how to submit a notifiable change through the online service.
For a quantity surveyor, the practical consequences are these:
- Do not treat your variation register as the statutory log. It is not the principal contractor's legal record, and it is not your document to maintain unless the appointment says so.
- Ask the principal contractor for the classification of each change. A change classed as notifiable or major may affect programme and cost while approval is pending, and your log should show that dependency.
- Cross-reference the two records. A column holding the statutory log reference against the commercial row lets anyone trace the same change in both places.
- If you are unsure which category a change falls into, or whether the building is in scope, take advice from the principal contractor, the principal designer or your client's building control adviser. Do not decide it from the commercial register.
The golden thread
The Construction Leadership Council describes good information management, the "golden thread", as a fundamental requirement for safety and accountability, with change control ensuring everyone works from the latest information (see its golden thread guidance summary). Its guidance on the site inspection process for new-build HRBs notes that changes before or during construction must follow Part 3 of the 2023 Regulations, and that the principal contractor must maintain a document for them.
Even off HRB work, the principle carries over. A BoQ change log that can be read by someone outside your team, and that points to the drawing revision behind every quantity, is closer to what the golden thread asks for than a spreadsheet only one person understands. For general reading on how documentation services approach keeping compliance records organised, this 2026 guide to financial compliance documentation covers a neighbouring field, though its focus is financial rather than construction.
Spreadsheet or software?
A spreadsheet is a perfectly reasonable change log for a small project. It needs locked column headings, a reference format, a status drop-down and a change history on the file. It starts to creak when several people edit it, when quantities are re-measured by hand after each revision, or when you need to show which drawing issue a number came from.
Whatever the tool, test it on three questions:
- Can you see who changed a row, and when?
- Can you trace each quantity to a drawing and revision?
- Can you reproduce the contract sum at any past date?
If the answer to any of them is no, the log is a list, not a record. Our overview of quantity surveying software benefits for UK professionals covers what to look for more broadly.
Where QuantiFlow fits
QuantiFlow reads construction drawings and produces a draft Bill of Quantities for a quantity surveyor to review and sign off. It is in development. If you want to follow it, see quantiflow.co.uk. The change log itself stays your professional record either way.
FAQ
Is a change log the same as a variation register?
In everyday practice, yes. Both describe the register of post-contract changes with their instructions, valuations and status. The statutory change control log for higher-risk buildings in England is a different document with its own legally required content.
How often should the log be updated?
RICS change control guidance points to at least monthly. Updating as each instruction arrives is better, because the reasoning is still fresh and the supporting documents are easy to find.
How is a change valued against the BoQ?
Under RICS NRM2, similar work is valued using the BoQ rates directly. Where no applicable rate exists, a new priced item is compiled in accordance with the contract's measurement rules. Your contract form sets the detail, so check the valuation clause.
Is a correction to an inaccurate BoQ quantity a variation?
Often, yes. Under many contracts the employer bears the risk of BoQ accuracy, so a correction is typically treated as a variation and re-valued at the BoQ rates. Confirm this against the clause in your own contract before recording it that way.
Do I need a change control log on every project?
The statutory log applies to higher-risk buildings in England under the 2023 Regulations. Other projects have no such statutory requirement, but a variation register is standard professional practice for controlling the final account.
Sources
- RICS: Change control and management
- RICS: NRM2 (October 2022)
- RICS: Valuing change
- The Building (Higher-Risk Buildings Procedures) (England) Regulations 2023, Part 3
- GOV.UK: Making changes to a higher-risk building project
- Construction Leadership Council: golden thread guidance summary
- Construction Leadership Council: site inspection process for new-build HRBs
Recommended
- Audit log best practices for UK quantity surveyors
- 10 BoQ Errors to Avoid: Audit Controls for Practising QS
- Seven BoQ Review Steps for UK QSs, Tied to Standards and Contracts
- Lock every BoQ line to its drawing revision: builder workflow for UK QS
This article is for general information only and is not professional, legal or commercial advice. Quantity surveying decisions should be taken by a qualified professional with reference to the specific project, drawings and contract in question. Content is produced with AI assistance and reviewed before publication. QuantiFlow Ltd accepts no liability for reliance on it.