Around 20% of global natural-disaster damage comes from rainwater flooding, and the average event in an industrial, commercial or public building costs roughly $2 million. The reason is structural: storms once designed as 1-in-100-year events now recur about once a decade, while urban infrastructure was engineered for the previous century's storms. This article explains the thinking behind the active blue roof - and why it changes the economics of runoff management for buildings and cities.
What exists today - and why it is not enough
The three standard solutions - infiltration wells, underground reservoirs and passive blue roofs - share two fundamental limits: they require significant construction works, and they are static. They are not synchronized with each other, they do not know a storm is coming, and they provide no real-time measurement of runoff volumes. A fixed orifice drains at the same rate on a sunny day and at the peak of the storm.
The active blue roof: temporary detention, controlled release
An active blue roof detains rainwater on the roof for a limited period, at the minimum depth set by the site's hydrological requirement, then releases it at a controlled, synchronized rate - typically the morning after the event. The core principles:
- The waterproofing is never touched - the system connects to the existing drain only; no drilling, no roof modifications.
- Temporary detention only - never a permanent reservoir. Water is released within hours, on schedule.
- Minimum water depth - set by the site's hydrological requirement, never more.
- Reduced required volume in reservoirs, wells and chambers - a direct saving in the project's below-ground budget.
The measured result: roughly 30% reduction in peak discharge from a single connected roof - measured in the field, on active deployments.
An add-on that fits every drain
The unit self-installs in minutes on any standard existing roof drain - 110 or 160 mm - with no changes to the roof or the drainage system. It needs only a nearby power socket; cellular communication is built in, so no new infrastructure is required. Installation takes up to 15 minutes per drain: prepare the socket, mount the unit, switch on.
The central safety principle is fail-safe: the valve is open by default. On any fault - power loss, communications loss, software failure - the valve stays open and the roof drains normally. Zero added drainage risk, with manual override available at all times.
Monitor. Adapt. Act.
A pressure sensor tracks the water level on the roof in real time. The algorithm combines the measured level with the weather forecast and the site's detention profile to compute the next valve state - adaptable to changing conditions over time. The valve opens and closes to a programmed percentage, and every action is logged with a timestamp and weather context.
Every roof, every storm - in one view
The cloud platform gives one unified view of every connected building: water levels, valve states, faults and rain events - all in real time. Per-building tailored alerts, rain-event reports built from measured data, and PDF/CSV export for authorities and insurers.
From building to city: a network of connected roofs
When every connected building reports to the municipal operations center, the authority gains direct oversight of runoff-policy implementation by contractors, automatic district-level regulation tuned to topography and infrastructure loads, and synchronization between districts based on real-time load. Over time, measured data becomes a planning tool: data-based zoning instead of estimates.
A real win-win: contractor and municipality
For contractors and developers: a fast answer to runoff regulation, a 15-minute-per-drain implementation, 5.5 points under the Israeli green-building standard with a downloadable justification document - and lower loads on basement piping, because a controlled morning release replaces a storm-peak burst. For municipalities and hydrologists: continuous compliance monitoring, real-time deviation alerts, rain-event reports from measured data, and district-level smart control.
Blue-green roof: one system
The same unit connects to an existing irrigation controller and uses the detained rainwater to irrigate rooftop vegetation. Runoff management and irrigation together: efficient use of the roof area, rainwater reuse, and vegetation fed by water that would otherwise have drained away.
Proven in the field
SmartFlow operates 17+ active deployments across Israel: a 14-site network in Acre, plus active sites in Tel Aviv, Jerusalem and Haifa. The system carries the Solar Impulse Efficient Solution label and builds on research foundations at the Technion. Want to see the data up close? Request a live site visit or a quote through the contact page.