Retrofit Projects are exciting as they represent a tremendous upgrade to aesthetics and environmental quality. Of course, they bring their own particular challenges that need to be addressed from an architectural and engineering standpoint. Here are some of the main considerations for retrofit green roofs.
- Determination of the construction, condition, and load capacity of the pre-existing roof and suitability to accept a LiveRoof.
- Determination of the condition of, remaining warranty lifetime, and terms or warranty of the existing waterproofing system as it pertains to being retrofitted with the new LiveRoof.
- Compatibility of the existing waterproofing system with the proposed slip sheet membrane.
- All the same issues regarding positive and negative wind pressure, slope, and forces against the parapet as they relate to new construction also apply to retrofit roofs.
LiveRoof is compatible with nearly any roofing system on the market. Over the years, we have seen our system successfully installed atop membranes manufactured by nearly every supplier in North America.
In recent years, more of these manufacturers have decided to introduce their own green roof systems. The quality and the integrity of these systems is variable, thus certain manufacturers have used warranty provisions to limit options for their customers to only system which they sell or market. The most common warranty used to control the green roof options are overburden removal warranties.
Overburden removal warranties cover the costs of removing and replacing the green roof system in the event of a roof leak. To make sourcing a single source warranty easy, LiveRoof, LLC has developed relationships with the following manufacturers who offer single source overburden removal and leak repair warranties:
Other membrane manufacturers may consider adding overburden removal coverage on a case by case basis.
When overburden removal coverage is not available from the membrane manufacturer, LiveRoof Overburden Removal Warranties may be purchased for terms of 10, 15 or 20 years. This warranty provides coverage for the costs to remove the green roof and to replace it after the leak has been serviced. Only Diamond Level LiveRoof Certified Installers are authorized to provide LiveRoof overburden removal coverage. Contact your local LiveRoof representative for referrals to qualified contractors in your region.
* Sika Sarnafil full system warranties may only be installed by Elite LiveRoof Installers and maintained by Elite LiveRoof Maintenance Contractors.
The slip sheet is the protective layer used between the modules and the membrane. The material is typically selected and provided by the membrane manufacturer.
For Conventional Membrane Roof Assemblies, we recommend a minimum 1-1.5 mm (40-60 mil) thickness with overlapped and effectively bonded seams to ward against root penetration and to keep waterproofing layer safe and clean from soil during installation.
Slip sheet/root barrier typified as follows: Welded Seam Types – 1 mm (40 mil) or greater thickness
-TPO, with seams heat welded
-PVC, with seams heat welded
-Polypropylene, with seams heat welded
-HDPE, with seams heat welded
Glued Seam Types – 1 mm (40 mil) or greater thickness
-EPDM, with seams overlapped a minimum of 75 mm and glued with roll out adhesive or double sided tape adhesive of the type that is impervious to and not affected by moisture, and recommended by the manufacturer.
-Low profile drain board of appx. 0.5 mm (17 mil) thickness, with edges overlapped 75 mm and glued with manufacturer approved adhesive.
For Protected Membrane Roof Assemblies, we recommend a minimum .25mm (10 mil) thick slip sheet of woven polyethylene or other non-moisture holding material to be installed above the membrane and below the insulation, as specified by membrane manufacturer.
A minimum .25mm (10 mil) thick slip sheet of woven polypropylene or other non-moisture holding material to be installed above the insulation and below the green roof modules, as specified by membrane manufacturer.
Do not use duct tape or adhesive for seaming that is not approved by the membrane manufacturer. Never use moisture holding fabric, such as needle-punched polyethylene or felt, under the green roof system. Such materials are trap aggregate and are impossible to sweep during installation and stay wet and encourage root growth and root penetration, which is especially detrimental if woody plants become established as such plants have woody root systems and may potentially cause roof leaks. This could lead to impeded drainage and compromise plant health.
In cases where electronic leak detection may be desired, a fiber-backed drainboard may be used. Fiber-backed drainboards are only recommended when electronic leak detection is desired, and only when vegetated with Sedums or Sempervivums, or other succulents, as these plants are sparsely-rooted and not prone to rooting into the fiber of the drainboard.