By: Marek Patrosz
May 26, 2021
In recent years, our building envelope consultants have been involved with designing a number of IRMA (Inverted Roof Membrane Assembly) roof systems with pre-cast or porcelain pavers that are installed on adjustable pedestals for. This system is ideal as a replacement for existing standard roof assemblies where flashing height restrictions prevent the use of a standard insulation, cover board and finish ply system.
Where a level pedestrian surface is required, an adjustable pedestal and paver system allows for versatility in choosing paver sizes, thicknesses, textures, and colors that generate aesthetic appeal for a roof deck or terrace. As vegetative roofs are becoming more popular, we have encountered challenges with many roof designs that required us to weigh the pros and cons of a vegetative roof system verses a paver roof system as well as adding additional structure to accommodate heavy planters into the paver roof system.
When designing roof decks and terraces that must accommodate both indoor and outdoor living spaces, a combination of pavers and vegetation is often the most desirable option. Without much change in the overall roof design, we found that utilizing vegetative tray systems, such as Sedumsod or LiveRoof, provide versatility, as well as biodiversity that can be tailored to a building’s requirements.
When choosing vegetative trays in the roof design, there are four key criteria that should be considered:
- Watering Requirements
When we think of weight, we typically think of the load on the roof structure; however, the weight aspect of vegetative trays tends to be more controlled by uplift weight rather than the weight imposed on the roof structure. Typically, a vegetative tray does not weigh more than a standard 2” x 24” x 24” Hanover Paver. However, a vegetative tray can be very lightweight when dry and become susceptible to uplift, and proper precautions must be taken to provide adequate edge protection and securement, especially on roofs with exposed edges.
The water requirements for vegetative trays can vary vastly based on the aesthetics and function, as vegetative trays can be utilized to reduce stormwater runoff if the suitable plants are chosen; at the same time, they can also provide abundant plantings with supplemental irrigation. The choice of one over the other is often influenced by climate. When considering water requirements, it is also important to keep in mind the corresponding required maintenance; in some cases, it may be beneficial to install indigenous plants that are best suited for the existing local climate, rather than to install an additional irrigation system at the roof level.
The most common vegetative trays utilize low ground cover plantings; however, low brush or elevated brush can also be achieved depending on the desired aesthetics. Trays can be installed to hide edges and create a vegetative zone, and can be used as edges to frame areas on a roof deck. There are many combinations that can be functional and balance a space depending on the desired integration between the planting and the paver system.
The integration of the roof vegetation with the paver system has many possible functions. The trays can be purposed as a visual garden, walking surface, pet area, and/or decorative element around the intended walking surfaces. Ultimately the type of tray and vegetative system will be determined by the roof terrace design. The versatility of the trays does not limit the variety of uses; the trays may be rearranged to adapt to the end user’s preferences. The next big challenge is deciding on your building’s perfect combination.