The construction diary and hidden works certificates are two documents whose absence comes to light at the worst possible moment – when the house is finished and you want the permit of use. You cannot "quickly do them" afterwards as if they had been made at the right time.
This guide sets out exactly what the law requires of the diary and certificates, who has to sign what, and what to do if the construction is done but the paperwork is not.
Who is required to document the work
The obligation does not depend on whether you build yourself or hire someone, but on which permit or notice the building requires. Under the regulation, construction must be documented in four cases:
- a building permit is required for the construction
- a building design must be submitted with the building notice (Annex 1 to the Building Code)
- a permit of use is required to use the building
- a building design must be submitted with the notice of use (Annex 2 to the Building Code)
If your building requires none of these – for example an ancillary building of up to 20 m² and up to 5 m high, which from 1 August 2026 needs neither a notice nor a permit – there is no formal obligation to keep a diary. But note: you still have to document the work to an extent that makes it possible, if needed, to establish with reasonable effort and cost that the building and the construction meet the requirements. In practice this means photos, invoices and a list of materials.
What the construction diary must contain
An entry is made for every construction day, and the entries are in chronological order. The law lists eleven data fields that each entry must contain at a minimum:
| Data field | What it means |
|---|---|
| Date of entry | The day the entry refers to |
| Name of the person making the entry | Who wrote the entry |
| State of the site and conditions | Weather, temperature, ground condition, obstacles |
| Description of work done | What was done that day – specifically, not "work was carried out" |
| Construction materials and products used | What went in and how much |
| Note on the hidden works certificate | If a certificate was drawn up that day, a reference to it |
| Date of waste removal | When the skip was taken away |
| Owner's supervision remark or recommendation | If there were any |
| Order from state supervision | If there were any |
| Name of the contractor and the competent person | Who did the work |
| Name of the owner's supervision provider and the competent person | Who checked |
One relaxation worth knowing
If the state of the site, the description of the work done and the materials used have not changed, you do not need a new entry for each day – the existing entry can be extended with the following dates. This is meant precisely for situations where the same work goes on for several days in a row.
Hidden works certificates: before covering, not after
A hidden works certificate is drawn up for the part of the building that is covered at the next stage and cannot later be inspected with reasonable effort and cost. The vapour barrier under plasterboard, rebar inside concrete, pipes under the floor.
The timing is set out unambiguously in the law: a certificate is drawn up for each work section or part to be covered before it is covered, but after the contractor's competent person and the owner's supervision provider's competent person have inspected the work.
Which works need a certificate
The law lists eighteen types of work. When building a private house, these come up most often:
- installing reinforcement or fixing elements cast into concrete
- installing a wind barrier, insulation, vapour barrier or waterproofing
- sealing wall, floor and ceiling junctions
- installing and sealing windows and doors
- installing the roof underlay, roof drain or roof gully
- installing a building service system or part of it
- installing pipework, drainage, wells, cables and penetrations
- installing a masonry heater and heating system penetration
- installing and sealing penetrations through fire-separating structures
- laying and compacting fill layers, if they will be covered
What the certificate must state
| Data field | Example |
|---|---|
| Name and location of the hidden work | Foundation waterproofing, axes A–D |
| Reasoned assessment of compliance | Complies with the design and the manufacturer's installation instructions |
| Other details of the work | Layer thickness, overlaps, material manufacturer |
| Inspection method or device | Visual inspection, tape measure, cover meter |
| Time of inspection | Date and, if needed, time |
| Name of the contractor and the competent person | Company and the specific person |
| Name of the owner's supervision provider and the competent person | Company and the specific person |
Who signs what
By signing, the signatory confirms that the work was done in line with the principle of professional competence. The signing rules differ by document type:
| Document | Who signs |
|---|---|
| Every construction diary entry | The competent person of the construction contractor |
| Hidden works certificate | The competent person of the construction contractor and of the owner's supervision provider |
| As-built drawing, test report, meeting minutes, maintenance manual | The author of the document |
| All construction documents, if you build for your own use | The building owner themselves |
Digital signature and signature on paper
A digital construction document must be readable with free software, must not contain changeable parts and must be digitally signed. If a document signed on paper is later converted to digital form, it does not need to be digitally signed as well.
When and how to submit to the Building Register
Construction documents are submitted to the Building Register electronically, at the latest together with the application for a permit of use or the notice of use.
- If no building design has to be submitted with the building notice, there is no obligation to submit the documents.
- If there is no obligation at all to file a notice of use or apply for a permit of use, construction documents are not submitted to the register.
- Documents not submitted to the register are kept by the building owner.
Extra requirement for businesses: machine-readable format
If you build as part of a business – that is, you are a construction company, not a private person building your own house – you must submit the documents to the Building Register in machine-readable form, not only as PDF. This applies if the building permit was issued or the building notice filed on or after 1 January 2021.
If construction is finished but the diary was not kept
This is the most common situation people come to us with. The building is finished and habitable, but nobody kept a diary and no certificates were drawn up. Honestly: you cannot, and must not, create documents after the fact as if they were "made on time".
What you can do is show, based on the evidence you have, that the building meets the requirements. The local authority does not expect a miracle – it needs to be satisfied that the building is safe and matches the design.
- 1.Gather what you have. Photos from the build, invoices, delivery notes, material packaging, messages with the builder, bank statements. Dates are worth their weight in gold here.
- 2.Draw up a summary sheet. A timeline of what was done, when and by whom – it takes the place of the diary in the proceedings.
- 3.Order a building audit. A competent structural engineer assesses the load-bearing structures, fire safety and compliance. The audit is what replaces the missing as-built documents.
- 4.Order the missing specialist documents. Electrical installation audit, chimney sweep's certificate, heating system assessment, as-built drawings for water and sewerage.
- 5.Draw up certificates retrospectively where you can. If you have photos of hidden work before it was covered, a certificate can be prepared from them – stating honestly that it was compiled afterwards from photos.
- 6.Submit the package with an explanatory cover letter. Set out what exists, what is missing and what the missing items have been replaced with.
How to make it easier for yourself
Keeping a diary usually fails not through ignorance but through fatigue. At the end of the day nobody feels like filling in a form. A few things that help:
- Make the entry straight away, not at the end of the week. A week later nobody remembers what the weather was on Wednesday or how many tonnes of crushed stone arrived.
- Photograph everything before it is covered. Every time something disappears from view – rebar, vapour barrier, pipework – take four or five photos so that the location can be identified.
- Keep the delivery notes for materials. They also prove which material went where.
- Also note down straight away anything done differently from the design. Deviations from the design are a separate issue and much harder to explain later.
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