Greening BC Skylines Together...
Editor’s note: We’re pleased to share this visual essay by our colleagues at Structural Monitoring Technology (SMT) about their work and direct experiences waterproofing through leak detection monitoring systems. All content is credited to SMT. As a neutral nonprofit, GRIN is committed to building awareness and debunking myths. The case studies illustrate how leaks on roofs are caused during construction (NOT by green roofs!). Enjoy and leave a comment below!
This inverted roof assembly is doubly protected by a green roof and a leak detection system.
Protecting Green Roofs as Assets
Green roofs are not only a protective layer over the structure, but also an asset for those who occupy it. Green roof benefits are well understood, including aesthetic and mental health benefits for occupants, sustainability benefits including carbon capture, stormwater retention, and extending the longevity of the roof. Some studies indicate a green roof may last twice as long as a generic flat roof, offsetting any higher upfront costs.
Like all flat roofs, green roofs rely on a waterproof membrane to keep water from penetrating the building. Once this waterproof membrane is covered with layers of insulation and green roof elements, finding any leak becomes very difficult. Fortunately, we have technology to determine the exact location of a breach of integrity. This is especially meaningful for large green roofs with a significant amount of overburden.
Over the last 20 years, Structural Monitoring Technology (SMT) has observed that the majority of issues imposing risks to the integrity of low-slope green roofs occur during construction. This is well-known and makes sense, given that the roof deck is used as a walkway, a staging area for materials and equipment, and is open to damages from above. For example, we have seen:
- Nails and other building materials embedded in the waterproof membrane.
- Chemical burns as adhesives used on walls and planters drip onto the membrane.
- Heavy equipment and scaffolding stored on wooden blocks digging into the protective waterproof barrier.
All these inconsistencies and damages to the waterproofing allow water into the roof deck where it can cause structural damage, disrupting the operation of the building and costing owners thousands, if not more, in repairs!
Above: Damages found in waterproof membranes during construction
What is leak detection?
Leak detection systems are designed to monitor the health of the waterproofing that covers the structural roof deck on a large low-slope roof. In this set-up, advanced low-profile sensor elements are permanently installed directly on top of the waterproof membrane, and connected to monitoring electronics. This system can monitor the health of the membrane from the moment it is installed, through construction as layers of insulation and vegetation are placed on top, and into the future.
Above: FutureCast Leak detection system installed within the layers of an inverted/ protected roof assembly
Given that leaks are costly and disruptive, these monitoring systems are excellent investments. Their value to a green roof extends well into the future, too, because these systems can actively monitor the now-hidden waterproof barrier and generate reports that guide building owners on when and where to conduct maintenance. Any repairs are then significantly reduced in cost because only targeted sections of vegetation need to be removed, which also minimizes disruption to the building occupants.
Case Study 1: Passive Leak Detection System Finds Leak
Installing a leak detection system on a green roof begins with architectural drawings. In this case study, SMT was contracted to install a leak detection system on a mid-rise building in downtown Vancouver featuring an extensive green roof plaza deck.
Above: Architectural drawings with leak detection system mapped out
Once the waterproof membrane was complete, SMT installed an extensive grid of sensors laying flat on top of the membrane. On this project, the sensors were left installed in a passive state (i.e. not actively taking readings of the roof environment).
Above: Leak detection sensors covering the roof deck, directly on the waterproof membrane
A leak detection scan was performed using a handheld DigiScan device, pinpointing damages to the membrane so they could be repaired before the membrane is covered.
Above: DigiScan device locates a penetration in the waterproof membrane
The leak detection system becomes part of the roof assembly, and overburden is placed on top of it. In this case, it was covered with a root barrier, drainage mat, insulation, growing medium and vegetation.
Above: Green roof installed on top of an inverted roof assembly
The green roof system was completed, with planters placed around the perimeter.
Above: Completed Green Roof
One fine day, a leak was discovered by a tenant, so we returned to site to activate the system and take readings of the membrane environment. Multiple readings with varying levels of rooftop saturation were taken and analyzed.
Above: Portable Leak Detection System Electronics
Data from the leak detection system was used to generate a “heat map” of the waterproof membrane, narrowing a search area for the source of the leak.
Above: CAD drawing illustrating the likely area of the leak (Credit: SMT Analytics)
As shown in the image below, the leak was uncovered in a corner of the roof. A small area of overburden was removed. This meant that tenants could continue to access and enjoy the majority of the roof. At the same time, it saved a lot of time and cost!
Above: Small area of exposed membrane for leak investigation
The exposed membrane was scanned with a DigiScan device to pinpoint the leak.
Above: DigiScan 360 device scans waterproof membrane, giving a vector towards the leak source
In this case, we discovered and located a damaged pipe. The system also indicated that the pipe was damaged further down on a different level, which allowed for a comprehensive repair.
Above: Damaged pipe located
The roof was re-covered and, as shown below, the impact was contained and subtle. The leak detection system is still used periodically to check on the health of the membrane and the success of the repairs.
Above: Fully Covered Green Roof
Case Study 2: Fully Automated Monitoring
In our professional opinion, the best protection for a green roof is a fully automated leak detection system. SMT has installed over 30 fully automated leak detection systems active across Canada and the United States, offering near-live performance data for the waterproof membranes protecting structures with green roofs.
On one such project, our FutureCast automated leak detection system triggered an alarm for a membrane breach. The system data highlighted a small area of the green roof for removal so that the breach could be found.
As per usual, the breach was caused during installation. In this case, a landscaping stone was placed as a walkway and barrier around the perimeter of the extensive green roof. Stones from this barrier were kicked under the drainage mat, allowing the full weight of the overburden to press the stone into the waterproof membrane. We have seen this kind of damage on multiple sites, and it’s especially pronounced where new details (e.g., lampposts, electrical outlets, benches) were added to the roof.
Above: Fully Covered Green Roof, Months into Building Operation
In Closing
Green roofs are excellent investments for the waterproofing, for the building beneath it and for the community nearby. As such, green roofs are installed with the expectations of longevity and resilience, with optimism even! Given how chaotic construction sites are, then, it is crucially important to implement best practices at time of installation. To protect that investment further, a fully automated leak detection system that lasts as long as the roof is an excellent long-term solution.
We’d love to hear from you. How did this article impact your understanding about roofs, in general, and green roofs, in particular? Do you have any experiences with leaks to building envelope? Use the comments below. Join our mailing list to receive news and updates on green roofs in BC straight to your inbox!