In an NBS specification, a roof leak detection system is classified under Uniclass 2015 as Ss_75_50_50_96 Water leak detection and alarm systems, and is best written as its own performance-based system clause, separate from the independent quality assurance of the waterproofing, which belongs in the roof waterproofing clause. This page gives the codes, says where each piece goes, and provides model clause text in the NBS system-clause shape you can adapt.
The rule for when to include each: every roof gets the quality assurance clause; any roof where the waterproofing will be covered (green, blue, inverted under ballast or paving, podium, buried, landscaped) also gets the permanent leak detection clause, because a covered membrane cannot be inspected. The decision in full is in should you specify leak detection in this roof?.
The reasoning behind each requirement — position, power, zoning, service life, commissioning and alarm ownership — is set out in how to specify a smart, integrated leak detection system in a roof build-up. This page is the drop-in version.
The Uniclass codes
| Table | Code | Title |
|---|---|---|
| Systems | Ss_75_50_50_96 | Water leak detection and alarm systems |
| Systems (parent) | Ss_75_50_50 | Liquid detection and alarm systems |
| Products (parent) | Pr_75_50_48 | Liquid-sensing devices |
| Products | Pr_75_50_48_60 | Pad leak sensors |
| Products | Pr_75_50_48_47 | Leak-sensing tapes |
| Products | Pr_75_50_48_96 | Water-sensing cables |
Source: NBS Uniclass 2015, Systems table v1.43 (July 2026). Ss_75_50_50_96 replaced the older Ss_75_50_28_96 and Ss_75_50_33_96, which are no longer in use — worth checking if you are working from an older specification. Uniclass maps it to NRM1 5.12.1 (Communication systems); agree with your cost consultant where it is carried.
A battery-powered sensor array is closest to Pr_75_50_48_60 (pad sensors). A conductive grid or tape system is closest to Pr_75_50_48_47 (leak-sensing tapes).
Two clauses, not one
| What you are specifying | Where it goes | Why |
|---|---|---|
| Permanent leak detection system — sensors or grid, monitoring, alarms | Its own system clause, Ss_75_50_50_96, with extent on the roof drawings | It is a separate system with its own products, power, commissioning and owner |
| Independent quality assurance of the waterproofing — inspection and integrity testing by someone who is not the installer, before cover and at completion | The roof waterproofing system clause, under execution and completion | It is a check on the waterproofing, done by a tester who reports to the Employer, at defined points in the programme |
The common failure is a single line — “integrated leak detection to the roof” — that leaves the tenderer to decide whether you meant a test, a system, or both. A well-specified roof that will be covered has both: the independent QA proves the membrane was sound when it was covered; the system reports what happens afterwards. See permanent monitoring vs electronic integrity testing.
Model clause 1 — permanent leak detection system (Ss_75_50_50_96)
Adapt bracketed values. Written as performance requirements so that more than one system can compete.
Ss_75_50_50_96 Roof leak detection and alarm system
Description: Permanent leak detection system integrated within the roof build-up, to the monitored extent shown on drawing [ref].
System outcomes
- Detects water entering the roof build-up through the waterproofing, and reports the affected zone, for the design life of the waterproofing without intervention.
- Raises an alarm to the nominated recipient(s) within [24] hours of a detection event.
- Provides a dated record of readings from commissioning onwards, owned by the Employer and exportable in an open format.
System performance
- Monitored extent: [all roof areas over internal occupied and plant spaces], as hatched on drawing [ref]. Areas over external space: [excluded].
- Localisation: [state either] detected water localised to a zone of not more than [ ] m² / breach located to a cell of not more than [ ] m².
- Service life without intervention: not less than [25] years or the warranted life of the waterproofing, whichever is greater. Submit evidence of service life [from an accredited test laboratory where available].
- Penetrations: no penetration of the vapour control layer or the waterproofing by sensors, cables or fixings, unless detailed and approved by the waterproofing manufacturer in writing.
- Compatibility: confirm suitability for the specified build-up, including membrane type, deck and overburden. Where the system relies on electrical conductivity across the membrane, confirm the build-up provides a conductive path (note limitations on black EPDM, foil-faced layers, isolated decks and timber decks); a conductive underlay added for this purpose is not accepted as a substitute for a compatible system.
- Data: Employer owns all data; export as [CSV / API] available for the life of the system; state the arrangements if the monitoring service ends.
Products
- Sensors / sensing layer: [Pr_75_50_48_60 pad leak sensors / Pr_75_50_48_47 leak-sensing tapes], manufacturer’s standard, or equivalent meeting the performance above.
- Gateways / control equipment: located and powered as shown on drawing [ref].
Execution
- Install in sequence with the roof waterproofing, to the manufacturer’s instructions and the approved layout.
- Record each sensor or zone on the roof plan as installed.
- Commission before the waterproofing is concealed, and only after the waterproofing has passed independent quality assurance (see roof waterproofing clause).
- Record baseline readings for every zone at commissioning.
System completion
- Submit: zone map; as-installed sensor positions; baseline readings; alarm route and named recipient(s); response period; written confirmation from the waterproofing manufacturer that the system does not affect the waterproofing guarantee.
- Include in the building owner’s manual, with the party responsible for monitoring and response after handover.
Model clause 2 — independent quality assurance of the waterproofing (in the roof waterproofing clause)
Insert under execution and completion of the roof waterproofing system clause. The standards call this integrity testing; the clause makes the independence explicit.
Independent quality assurance of waterproofing
- Inspect and test the waterproofing for integrity by [low-voltage electronic leak detection / high-voltage electronic leak detection / both], carried out by a tester independent of the waterproofing installer and the membrane manufacturer, appointed by or reporting to the Employer [and a member of RAWTA or demonstrably equivalent].
- Where the membrane cannot be tested electronically (for example black EPDM or foil-faced bitumen, or where the deck is electrically isolated), carry out the alternative method agreed with the designer [visual inspection with seam probing / flood test / other]. A conductive underlay is not accepted as a means of making an otherwise untestable build-up compliant with this clause.
- Timing: before temporary protection is installed, and again after it is removed, in accordance with BS 6229:2025 clause 6.2; and before any overburden, paving, green roof or blue roof components are placed.
- Repair all defects and retest. Do not conceal the waterproofing until it has passed.
- Report: test method, extent, defects found and repaired, retest results, photographs, and the tester’s competence. [On NHBC-warranted homes: make the report available to NHBC, and state the test method in the design information, per NHBC Standards 2026 Chapter 7.1.]
- Liquid-applied systems: test in accordance with LRWA Guidance Note 18.
What to cite, and what not to
Cite with confidence
- BS 6229:2025 clause 6.1 (electronic leak integrity testing among the compliance tests to agree) and clause 6.2 (test before temporary protection and after removal). Neither names independence; the independence requirement is yours to write.
- NHBC Standards 2026, Chapter 7.1 — integrity testing on roofs over 50 m² or hard to access, report to NHBC; green roofs tested before covering; test method in the design information.
- BS 8102:2022 §6.5 Note 2 — accepts warm roof build-ups and loose-laid waterproofing on buried decks where permanent leak detection is employed such that leak locations can be identified and repairability is achieved.
- CIRIA C817 §3.2.3 — on warm blue roofs, a permanent leak detection system should be considered.
- LRWA GN18 — electronic integrity testing of liquid-applied membranes.
- ASTM D7877 and ASTM D8231 — electronic leak detection methods (D8231-24a supersedes D8231-19).
Treat with care
- “Compliant with ASTM D8551.” D8551 covers permanent monitoring of geomembranes in containment — ponds, landfills, tanks — not building roofs, and it expressly declines to cover moisture-detection systems. Ask what the claim means before accepting it.
- Any claim that a standard requires permanent monitoring on your roof. No UK standard or warranty body that we know of does. What NHBC requires, and BS 6229:2025 recommends, is integrity testing. The case for permanent detection on a covered roof is a design argument, not a compliance one, and it is a strong one.
- A conductive underlay offered to make a build-up testable. Our view is that it adds little, and on an inverted roof, where the membrane already sits on concrete, nothing. If the build-up cannot be tested, change the build-up or agree a different QA method.
- Service-life claims of 20–30 years. These are calculations. Ask what reporting interval and signal conditions they assume.
Related reading
- Start here if you are deciding whether this roof needs leak detection: Should you specify leak detection in this roof?
- Start here if the roof feels high-risk: High-risk flat roof? How to reduce the risk
- How to specify a smart, integrated leak detection system in a roof build-up — the reasoning behind each clause
- What are the best smart roof leak detection systems? — the systems on the market
- Electronic leak detection — the complete UK guide
- How many leak sensors does a roof need?
Vector will mark up your roof waterproofing and leak detection clauses as part of a waterproofing design review. Send us the specification.