For architects
Designing for Sensor-Based Leak Detection
A practical guide to integrating permanent moisture sensors into warm and hybrid roof build-ups — what the standards now require, where sensors actually work, and when they're justified.
The design-stage opportunity
Most conversations about leak detection happen after a building leaks. By then the options are forensic, expensive and disruptive.
The architects we work with are increasingly asking a better question: what should we be doing at design stage to make leaks easier to find — or stop them being a problem at all?
This page is written for that conversation. It's not a product pitch. It's an honest look at how sensor-based leak detection works in practice, which roof build-ups suit it, and where the design decisions you make now will determine whether sensors deliver value later.
If you want an independent review of a specific design, see our Waterproofing Design Review service — typically free of charge.
The compliance context
Permanent leak detection is no longer a "nice to have". The standards have moved.
BS 8102:2022 — protection of below-ground structures
Section 6.5 Note 2 states that warm roof build-ups and loose-laid waterproofing systems are acceptable on buried decks where permanent leak detection systems are employed (cross-referencing Section 4.3.2). For landscape roofs, podium decks, basement decks and buried waterproofing build-ups, sensor monitoring isn't optional — it's a compliance enabler.
BS 6229:2018 — flat roofs with continuously supported flexible waterproof coverings
Note 2 to Clause 8.2 recognises that electronic devices are available to detect leaks and heat loss. Section 6.1(s) names electronic leak integrity testing among the compliance testing requirements to be communicated at design stage.
CLT and mass timber
BS 6229:2018 Section 5.2 calls for inspection and testing regimes both during construction and throughout the service life of CLT and mass timber elements. The 2024 Joint Code of Practice identifies moisture content as the key factor for mass engineered timber.
CIRIA C817 — blue roofs
CIRIA C817 is the definitive UK guidance on blue roof design, implementation and monitoring. Section 3.2.3 calls for permanent leak detection systems on warm blue roofs. Vector's Ben Hickman was a Key Technical Author of this publication.
The build-ups that work for sensors
Warm deck — best fit
A continuous platform beneath the waterproofing. Moisture spreads predictably and sensors pick it up wherever it arrives. NHBC has effectively walked away from cold decks — the industry is moving here anyway.
Hybrid deck — workable
Some insulation between joists, some above. Behaves enough like a warm deck for sensors to perform properly. Often the right answer when headroom is tight.
A note on cold decks. Cold deck construction adds complications that fall outside the scope of this page. If you're working on a cold deck project where sensor monitoring matters, get in touch.
What the sensors actually look like
Size
Approximately the dimensions of an ice hockey puck.
Depth
~40 mm — fits within most insulation gaps.
Weight
Very light, easily handled in one hand.
Power
Battery powered — crucially not mains.
Why battery matters: a mains-powered sensor needs a cable run, and a cable run almost always means a penetration through the waterproofing. Battery life is measured in years.
Where to place them
In a warm deck
Directly on the deck, beneath the waterproofing.
In a hybrid
On the deck within the warm portion of the build-up.
On a refurbishment
A 100 mm cylinder of insulation is removed and replaced around the sensor, with a 100 mm membrane lap restoring the waterproofing above.
When is a sensor system justified?
Sensors make most sense where:
- The asset has high value and a leak would cost significantly more than the system to install
- The roof carries finishes that make leak location difficult — green roofs, paved terraces, running tracks, mature planting
- The roof sits above sensitive use — data centres, archives, premium residential, server rooms, art storage
- The client wants the certainty that comes with knowing about a leak in hours rather than months
If the building is a low-rise warehouse with a bare membrane and easy access, sensors are probably not the right spend.
Think of sensors the way you'd think of tyre pressure sensors on a car. On the right asset, that's a transformative capability. On the wrong asset, it's an unnecessary feature.
How Vector fits in
Three services cover the full sensor lifecycle. They can be taken individually or as a single appointment under our Complete Roof Assurance offer.
At design stage
Waterproofing Design Review. Independent check on your section, sensor layout opinion, performance-spec language contractors can price. Typically free of charge.
During construction
Quality assurance inspections, sensor commissioning, integrity testing of the membrane before it's concealed.
Post-completion
Permanent Leak Detection & Sensor Monitoring. Continuous monitoring, real-time alerts, biannual roof inspections to BS 6229:2018 Clause 8.2, planned preventative maintenance.
Vector's technical director Ben Hickman was a Key Technical Author of CIRIA C817 (Blue Roofs).
Who this suits
- High-value commercial — data centres, headquarters, mixed-use
- Premium residential — particularly schemes with hidden roof finishes
- Cultural and institutional buildings
- Any roof where access for leak investigation will be difficult after handover
Submit your design for review
Send us your section. We'll come back with a sensor-layout opinion, a coverage assessment, and an honest view on whether this is the right system for your project.