Metropolitan Engineering Consulting and Forensics

GREEN BUILDING CONSTRUCTION DEFECTS

A vegetated roof cover is a veneer of vegetation that is grown on and covers an otherwise conventional flat or pitched roof, endowing the roof (< 30 degree slope) with hydrologic characteristics that more closely match surface vegetation than the roof. The overall thickness of the veneer typically ranges from 2 to 6 inches and may contain multiple layers, consisting of waterproofing, synthetic insulation, nonsoil engineered growth media, fabrics, and synthetic components. Vegetated roofs, also called “green rooftops” can be optimized to achieve water quantity and water quality benefits. Through the appropriate selection of materials, even thin vegetated covers can provide significant rainfall retention and detention functions.

Depending on the plant material and planned usage for the roof area, modern vegetated roofs can be categorized as systems that are intensive, semi-intensive, or extensive. Intensive vegetated roofs utilize a wide variety of plant species that may include trees and shrubs, require deeper substrate layers (usually > 4 inches), are generally limited to flat roofs, require „intense‟ maintenance, and are often park-like areas accessible to the general public. Extensive vegetated roofs are limited to herbs, grasses, mosses, and drought tolerant succulents such as sedum, can be sustained in a shallow substrate layer (<4 inches), require minimal maintenance once established, and are generally not designed for access by the public. These vegetated roofs are typically intended to achieve a specific environmental benefit, such as rainfall runoff mitigation. Extensive roofs are well suited to rooftops with little load bearing capacity and sites which are not meant to be used as roof gardens. Semi-intensive vegetated roofs fall between intensive and extensive vegetated roof systems

All well-designed extensive vegetative roofs include subsystems responsible for:

Drainage: Vegetative roof drainage design must both maintain optimum growing conditions in the growth medium and manage heavy rainfall without sustaining damage due to erosion or ponding of water.
Plant nourishment and support: The engineered medium must be carefully designed to provide for excellent plant growth, no wind scouring, and proper water holding capacity.
Protection of underlying waterproofing systems: Vegetative roof assemblies must protect the underlying waterproofing system from human activities (including the impact of maintenance) and biological attack, and solar degradation.
Waterproofing systems: Waterproofing is critical for protecting the structure from water intrusion.
Insulation systems: Insulation is critical for saving energy.

Figure 2. Generic Extensive Green Roof on a Concrete Deck

(Image courtesy of American Hydrotech)

Figure 3. Generic Extensive Green Roof on a Steel Deck

(Image courtesy of American Hydrotech)

A wide range of methods can achieve these functions. For instance, drainage layers may consist of plastic sheets, fabric or synthetic mats, or granular mineral layers. Similarly, the physical properties and performance characteristics of growing media (engineered soils) and plant materials may vary with the climate, plant community, or engineering requirements. Figure 2 shows a generic cut-away of a common type of vegetative roof assembly that utilizes a lower granular drainage layer in combination with an upper growth medium or substrate.

The selection of a particular approach may depend on performance-related considerations, such as runoff control, drought-tolerance, biodiversity, appearance, or accessibility to the public. While many pre-engineered systems are currently available, it is frequently necessary to customize these systems to satisfy specific performance objectives.

CONSTRUCTION DEFECT SERVICES

Metropolitan specializes in addressing and resolving disputes involving public work projects, business/commercial disputes, complex construction defect, environmental health and safety issues, construction delay and contractual matters, partnerships, homeowners association, retail centers, and real estate issues. Our three decades of forensic experience includes advanced research and analysis of code, materials and building practices, as well as the development of comprehensive repair methodologies for maximization of repair and restoration efficiency. We have financial and legal education, expertise and experience that we used to better focus our engineering arguments and presentations to the various parties. We have successfully participated in dispute resolution mediation, arbitration, and settlement procedures on numerous occasions.

Metropolitan’s design experience includes civil site improvements for single family housing, multi-family housing, commercial and industrial land development, roadways, public works construction, pipelines, reservoirs, pump stations, hydraulics and hydrology, and environmental impacts of construction defects. We are also proficient in all aspects of claims handling and management, including damage, liability and coverage issues, reserving, risk transfer, auditing, litigation management and expense control measures.

Metropolitan has extensive experience in the fields of moisture/water infiltration/intrusion, roof system failures, lath, plaster, mortar, stucco, drywall, dimensional stone, handset applications, prefab installations, light-gauge metal stud, fireproofing, architectural pre-cast concrete, and EIFS for all types of facilities. Our skills and experience include design, construction estimating, material take-offs, site inspection, corrective construction detail, scheduling, subcontractor and field crew coordination, contract drafting and execution, worker and environmental health and safety.