Site Diary: The Complete Guide to Construction Site Diaries
A site diary is a daily written record of everything that happens on a construction project: who was on site, what work took place, what went wrong, and what changed. It is the single most important document you will produce on any contract, and most teams get it badly wrong.
Will Doyle
Updated September 2026 · 18 min read
On an NEC4 project, site diaries help the commercial team identify potential compensation events and support cost and programme assessments. A diary entry is evidence; it is not automatically a contractual notification.
A diary written on the day is how you prove what happened. A Friday catch-up is not.
A construction site diary is a contemporaneous, chronological record of daily events on a building or infrastructure project. Weather, labour, plant, materials, instructions, delays, visitors, safety observations, and anything that departed from the Accepted Programme.
People forget. Diaries don't.
The commercial test is whether the record explains what happened, where, when and with what effect. Record the facts promptly and route potential contractual actions for review without waiting for a later cost reconciliation.
Call it a building site diary or just the diary. The job is the same: write a record today that protects the commercial position tomorrow. For entry structure, see how to write a site diary.
Why Site Diaries Matter Commercially
Change that is never written down is hard to recover months later, and the cost usually lands on the contractor. We deliberately do not attach a percentage or a headline sum to that: we have no independently checked dataset for it, and the exposure depends on the contract, the selected option and how the team works.
Site diaries matter for three reasons: they are the evidence for compensation events, they protect the programme position, and they support final account negotiations.
Under standard NEC4 ECC clause 61.3, the eight-week time bar runs from becoming aware that an event has happened, subject to the exception for events the Project Manager should have notified. Check amendments and issue the required notification separately; a diary entry alone is not enough.
Illustrative example: using a diary to investigate a potential event
Scenario: 12 March 2025, £28M rail electrification package under NEC4 Option C. The site diary records: "Client utility diversion works ongoing in Section 4 (chainage 1200-1400). Our piling rig unable to access Grid K3-K8 as planned on Accepted Programme Rev 3. Rig and 4-person crew stood down from 07:30. Access expected to resume 14 March per verbal instruction from PM at 09:15."
What happens next:
The QS reads this entry during the weekly diary review on 14 March
Check whether the facts meet clause 60.1(2), concerning access, or clause 60.1(5), concerning work by the Client or Others. Their conditions differ; an access problem does not automatically satisfy either provision.
The QS checks the awareness date, notification responsibility and any exception or amendment, then issues the required communication through the contractual system.
For illustration, two days of a rig at £3,200 per day and four operatives at £280 per day totals £8,640. These assumed rates and durations require assessment under the applicable Defined Cost rules; Fee and time effects are separate.
The diary supports investigation. It does not establish a final compensation-event value or a 1.5-day change to the Completion Date without the required cost and programme assessment.
This is an illustrative scenario, not a reported recovery. Prompt diary review helps the team investigate and notify potential events while relevant facts are available; it does not guarantee entitlement.
Illustrative example: separating weather measurements from site effects
Scenario: Week commencing 3 February 2025, £42M flood defence scheme under NEC4 Option A. The site diary records weather at 07:00, 12:00, and 17:00 each day:
Date
07:00
12:00
17:00
Rainfall (mm)
Mon 3 Feb
4C, heavy rain
5C, drizzle
4C, overcast
18mm
Tue 4 Feb
3C, sleet
2C, snow
1C, clear
12mm
Wed 5 Feb
-1C, frost
3C, clear
2C, clear
0mm
Thu 6 Feb
2C, heavy rain
4C, rain
3C, drizzle
24mm
Fri 7 Feb
5C, overcast
6C, clear
4C, clear
2mm
The diary also notes: "Earthworks suspended Mon-Tue and Thu due to saturated formation. Piling continued all week (unaffected). 12 earthworks operatives redeployed to drainage works Mon/Tue; stood down Thu as drainage works also weather-dependent."
The daily entries show possible site effects, not proof of a qualifying weather event. Clause 60.1(13) requires the specified calendar-month measurement, contractual location and historical comparison. Individual wet days at the nearest station are not the test. If an event qualifies, assess its effects under the contract; these records alone do not establish a £47,600 entitlement or a two-day Completion Date change.
Without detailed weather records? The QS would need to reconstruct conditions from Met Office data alone, with no proof of actual site impact. "It rained" does not tell you earthworks stopped. The diary does.
What to Record in a Site Diary
The golden rule: if it happened on site today, write it down. If it was different from what was planned, write it down in detail.
At minimum, every entry needs weather, labour, plant, work completed, instructions, delays, visitors, safety, deliveries and photos.
Category
What to Record
Why It Matters
Date and weather
Conditions at 07:00, 12:00, and end of shift. Temperature, wind, rainfall
Weather is a compensation event trigger under clause 60.1(13)
Labour
Numbers by trade, by subcontractor, hours worked
Proves resource levels for disruption claims
Plant and equipment
What was on site, what was working, what was idle
Standing time supports time-related cost claims
Work completed
Location, activity, quantities where possible
Progress evidence for programme updates
Instructions received
Who gave them, what they said, when
May constitute a compensation event under clause 60.1(1)
Delays and disruption
What stopped, when, why, impact on planned activities
Foundation for every CE notification
Visitors
Who visited, purpose, any instructions or comments
Client instructions can trigger CEs
Safety observations
Incidents, near misses, inspections
CDM 2015 compliance and RIDDOR reporting
Material deliveries
What arrived, quantities, condition, any rejections
If the diary is sitting in the cabin unread, the eight-week clock is already running. Rosie reads those entries against the contract so the commercial team sees the compensation event while the record is still warm.
Site diaries are one source of evidence for NEC4 administration. The Scope may specify particular record requirements. A diary supports the contractual processes but does not replace notices, applications or programme submissions.
Clause 61.3: record when the Contractor became aware that the event had happened, check who should notify it and apply any exception or amendment. The diary may help establish awareness; it does not conclusively fix the date in every case.
Clauses 31 and 32: site records help explain actual progress and programme revisions. Submit the programme information the contract requires. A diary does not replace the Accepted Programme or its acceptance process.
For cost-based options, inadequate accounts and records may be relevant to Disallowed cost. Apply the selected option and the specific definition to the queried amount; absence of a particular diary entry does not automatically disallow every cost.
Site Diary vs Daily Allocation Sheet
This causes more confusion than it should. They are different documents with different purposes, and you probably need both.
A site diary records what happened: events, conditions, problems, progress. It is a narrative account of the day.
A daily allocation sheet records who did what: which operatives were assigned to which tasks, for how long, in which locations. It is a resource deployment record.
Feature
Site Diary
Daily Allocation Sheet
Primary purpose
Record events and conditions
Record resource deployment
Who writes it
Site engineer, foreman, or site manager
Foreman or supervisor
Format
Narrative with structured fields
Tabular: names, tasks, hours, locations
Commercial use
CE evidence, delay narrative, compliance
Labour cost substantiation, productivity analysis
Contractual basis
Supports clause 61, 62, 63 claims
Supports Defined Cost records under clause 11.2(23)
On well-run projects, these feed into each other. The allocation sheet tells you the resource input. The diary tells you the context and output. Together, they give you the full picture.
Another common question. A site diary and a daily report overlap, but they serve different audiences and have different levels of formality.
A site diary is typically an internal contractor document. It is contemporaneous, factual, and written for the project team and commercial function.
A daily report (sometimes called a daily site report or construction daily log) is often a formal document submitted to the client, the Principal Contractor, or the project management team. It may include a narrative summary, progress photos, and KPI data.
Some organisations merge these into one document. That can work, but be careful: anything you submit to the client becomes disclosure. Keep your internal site diary honest and unfiltered. Your daily report might need to be more measured. I have seen too many projects where the combined document gets sanitised for the client's benefit, and the commercial team loses the unvarnished version they actually need at final account.
There is a distinction in who writes what, too. The foreman report covers gang-level detail that feeds into the broader diary. On a large project, the foreman's report and the engineer's site diary serve different levels of granularity, and you want both.
If you are coming from US terminology, see site diary vs daily log for how the UK and US terms map to each other.
Digital Site Diaries vs Paper Logbooks
Paper diaries still dominate on many UK sites. The supervisor grabs the A4 hardback from the site cabin, writes it at the end of shift, and puts it back on the shelf. It works. Until someone asks for Phase 2 in a hurry and the cabin has gone back to the hire company.
A digital site diary for NEC4 work does not have to replace the cabin habit. It has to make the record searchable when the QS is writing the quotation. Timestamped entries. Photos sitting with the words, not in a camera roll. More than one person contributing without fighting over one book.
The commercial question is not which app looks modern. It is whether the QS can find the access restriction from 12 March before clause 61.3 runs out. Offline capture still matters on remote sites. So does a format a site engineer will actually complete at 17:30.
Rosie does not replace the diary. She reads it against the NEC4 contract and the Accepted Programme, and flags the events a tired Friday review will miss.
Common Mistakes That Cost Money
I have reviewed hundreds of site diaries across NEC3 and NEC4 contracts. The same problems come up on nearly every project, and honestly, some of them are painful to see.
1. Writing the diary days later. Friday afternoon catch-up sessions are not contemporaneous records. Adjudicators can tell when entries have been batch-written, and they discount them accordingly. Write the diary on the day. Every day. No exceptions.
2. Recording activities but not deviations. "Concrete pour Bay 4, 45m3" is fine for progress. But if the concrete arrived 3 hours late because the batching plant broke down, and that pushed the pour into overtime, that deviation is where the money is. Record what went wrong, not just what went right.
3. Using vague language. Record the weather, affected location, timing, resources and work interrupted. Specific factual records support assessment; they do not guarantee payment.
4. Not escalating potential events. Flag access restrictions and work by the Client or Others for commercial review. Check the distinct conditions of clauses 60.1(2) and 60.1(5) before choosing a contractual basis.
5. Only the foreman writes it. On a £30M project with 150 operatives across six work fronts, one person cannot see everything. Multiple contributors, whether through a shared digital system or separate section diaries that are collated, give you complete coverage.
6. Ignoring weather evidence. Record site conditions and effects, and obtain the measurements required by Contract Data for the calendar-month test under clause 60.1(13). Site observations and contractual weather measurements serve different purposes.
7. Not taking photographs. A photo with a timestamp and location tag is evidence that is almost impossible to dispute. Conditions, progress, problems, access restrictions: photograph everything. Storage is cheap. Losing a £200,000 claim because you cannot prove the access road was flooded is not.
8. No weekly commercial review. The diary is only half the job. Someone from the commercial team needs to review entries every week, cross-referencing against the programme and contract. If the QS only reads the diary at final account, they will find the evidence but miss the deadlines. Gather automates this review process, but even without software, a 30-minute weekly review catches most issues.
Related Guides
This pillar page gives you the overview. The guides below go deeper on each topic.
Site diaries feed earned value tracking because progress and resource data are the raw inputs. For how a diary sits next to other daily records, see daily report vs site diary.
Legal and Retention
No UK statute requires a site diary by name. CDM 2015 and the Building Safety Act 2022 still make contemporaneous records expected professional practice. Under the Limitation Act 1980 keep records at least 6 years from completion, or 12 years if the contract is a deed. See record retention.
Site records, assured
See how Rosie reads a site diary against the contract
On a typical NEC4 project, thin diary records mean legitimate change goes unrecovered. The commercial team should review the diary every week against clause 60.1, not at final account.
A site diary is a dated record of what happened on site. On an NEC4 project it can support event identification and assessment alongside contractual communications, programmes, accounts and other evidence.
Is a site diary a legal requirement in the UK?
No UK statute requires a site diary by name. However, the Construction (Design and Management) Regulations 2015 require records of health and safety arrangements, and the Building Safety Act 2022 requires a golden thread of information for higher-risk buildings. In practice, meeting these obligations without a site diary is extremely difficult. Most standard form contracts and adjudicators treat site diaries as expected professional practice.
Who should write the site diary?
On most projects, the site engineer or foreman writes the diary, with contributions from supervisors across different work fronts. On larger projects (over £10M or with multiple active areas), multiple contributors are essential because no single person can observe everything. The commercial team should review entries weekly to identify potential compensation events or claims triggers.
How often should a site diary be completed?
Every working day, without exception. Entries should be written on the same day, ideally before leaving site. Courts and adjudicators give significantly more weight to contemporaneous records (written on the day) than to entries reconstructed days or weeks later. If you miss a day, note the gap honestly rather than backfilling.
What is the difference between a site diary and a daily allocation sheet?
A site diary records events and conditions (what happened). A daily allocation sheet records resource deployment (who did what, where, for how long). The diary is narrative and contextual. The allocation sheet is tabular and quantitative. Both are needed for comprehensive commercial records, particularly under NEC4 where Defined Cost substantiation requires detailed resource records.
How long should I keep site diary records?
Under the Limitation Act 1980, the minimum is 6 years from project completion for simple contracts, or 12 years if the contract is executed as deed. For projects involving personal injury risk, 15 years is prudent. For higher-risk buildings under the Building Safety Act 2022, records should be retained for the lifetime of the building. See our detailed guide on record retention periods.
Can a site diary be used as evidence in adjudication?
Yes, and it is often the most persuasive evidence available. Adjudicators routinely prefer contemporaneous site records over witness statements prepared for the proceedings because diaries are created in real time without litigation in mind. The key requirements are that entries are genuinely contemporaneous, factual, and specific. Vague or retrospective entries carry little weight.
How do site diaries support NEC4 compensation events?
Site diaries can help establish events, awareness and resource effects. Read them alongside instructions, notices, programme information, accounts and forecasts. They do not themselves notify a compensation event, guarantee entitlement or replace the dividing-date assessment rules.
What should I do if I have fallen behind on site diary entries?
Start again today. Do not try to reconstruct the past from memory, because those entries will not be contemporaneous and will carry little evidential weight. Note the gap honestly ("No entries recorded 14-18 March due to site engineer absence") and ensure entries are maintained daily going forward. One week of missing records is recoverable. Three months of missing records during a critical programme period can cost you the entire commercial position on delayed works.
Should site diaries be digital or paper?
Both work if used consistently. Digital site diary software offers advantages in searchability, backup, photo integration, and multi-user access. Paper diaries are simpler and do not depend on connectivity or device availability. The critical factor is not the medium; it is the discipline. A paper diary written every day beats a digital system that nobody opens. For most Tier 1 contractors, digital is now standard because of the volume of data and the need for rapid retrieval during disputes.
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