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Low Slope Roofing

Low slope roofing is often synonymous with “commercial roofing”. This is because commercial buildings typically have “flat” roof design, but many apartment buildings and townhouses have low slope roofs.

Professional Roofing Contractors perform new construction, roof replacement, roof recover and repair services on many flat or low sloped reflective, ballasted, vegetative or photovoltaic covered rooftops, throughout the Chicagoland area.

Types of Materials used on Flat Roof Assemblies:


Built Up (BUR)
BUR consists of layers of asphalt or coal-tar pitch, (bitumen) hot or cold applied, in between layers of reinforcing plies, fabric, felt or mat. The reinforcing is rolled into the bitumen for stability and reinforcement. There can be 3, 4 or 5 layers of bitumen and plies used to provide a thick, redundant, long lasting assembly. Each layer adds waterproofing and longevity.

Photo courtesy of CRCA

Modified Bitumen
Modified bitumen membranes are hybrids of the built-up system. They are a pre manufactured composite of rubber or plastic modified asphalt (or coal tar) and layers of a fabric or fiberglass mat reinforcement.  

The modified bitumen products are supplied in rolls. The modification of the asphalt or coal tar with rubber or plastic allows for better low temperature weathering performance and elongation characteristics.

These products typically use a one or two ply built-up membrane  before application of the final modified bitumen membrane.

Modified bitumen membranes can be torch applied, self-adhered or mopped in place with hot bitumen. They are always surfaced with some type of Topping System including factory-applied granules, gravel in adhesive or a compatible reflective coating.

Photo courtesy of CRCA

Single Ply
Single Ply roofing systems are just that, a single ply of a roofing material made from several types of polymer plastics and rubbers. The Single ply roof membranes are ballasted, mechanically attached or adhered to insulation or other substrates. Single ply materials provide one ply of material to protect the building instead of the multiple layers in a built up or modified bitumen roof membrane. Single ply membranes include those products made from EPDM, PVC, TPO and other formulations.

EPDM (Ethylene Propylene Diene Monomer)
EPDM is a rubber material that is supplied in large sheets for application on a roof. The material can be loose laid and ballasted with round, river washed rock or pavers to hold the membrane in place. The EPDM roofing membrane can also be adhered as well. Seams and the membrane are adhered with contact adhesives, with seams sometimes treated at the edges with a sealant. Toppings such as ballast or a reflective/protective coating may or may not be required by the manufacturer. This product is available in black mostly.

PVC (Polyvinyl Chloride)
PVC roof membrane materials are suppliedin rolls, and typically mechanically fastened to a roof deck assembly. Long screws and screw plates (large washers) are used to hold the roof membrane to the roof assembly. Seams are heat welded together, and sometimes sealed with a lap sealant. PVC membranes are reinforced with a fabric scrim, and available in tan and white colors. A topping material may not be required on this membrane.

TPO (Thermoplastic Polyolefin)
TPO roof membranes are typically fleece backed membranes that are adhered with adhesives to insulation.  These products are typically white in color, and may be reinforced. There may or may not be a topping system of gravel, ballast or a reflective coating required by the manufacturer on these systems.


Overburden Systems
Any of the roof membranes may require some kind of topping to hold the membrane in place (ballast, paver, small river rock adhered in hot or cold adhesives or vegetative coverings.   The Toppings protect the roof membrane from damage, hold the roof membrane down during wind events, stop Ultra Violet Light from attacking the material – and save it from general abuse.

Photo courtesy of Omni Ecosystems. Roof Installed by Bennett & Broseau

Vegetative Roof Overburden for Garden Roofing Systems
The Vegetative Roofs provide environmental benefits in addition to holding down the roof insulation and membrane.  The environment is better since plants provide reduced rooftop surface temperatures, oxygen back to the air and water retention in the soil media for a period of time. Holding water on the roof slows water flow into sewer systems – especially important in older cities like Chicago. CRCA has been at the forefront of this movement and its contractors install these complicated assemblies because they understand how to treat the critical element under the overburden- the roof membrane.

The 'overburden' for these vegetative roof systems is either hand placed and layered soil growing media, or pre-fabricated trays, with growing live plants delivered to the roof for placement by roofing contractors to specifications.

Vegetative Roofs may also meet code requirements for reflectivity of roofing in urban areas, reducing the Urban Heat Island Effect. The UHI effect was the subject of the 2009 Chicago Energy Code. 

Garden Roofs are available in two types: Intensive and Extensive Systems:

Extensive Systems typically use a thin layer of growing media soil and plantings on top of the roof assembly, allowing use on buildings where a ballasted single ply roof system may have been used.  Prefabricated tray systems can be classified as an Extensive Roof, and are provided by CRCA Members.

Intensive Systems assemblies use a heavier layer of soil and larger planting including shrubs, trees and other plants.

Photovoltaic (PV) Devices – Professional Roofing and Waterproofing Contractors also install photovoltaic devices on rooftops.  The PV converts solar energy to electricity reducing the demand for power from fossil fuel and nuclear power plants. Before installing PV on the roof, it is important to understand the roof life expected post PV installation. Since payback can be 20+ years for the PV, the roof needs to outlast the payback period as it’s hard to remove the PV. 

Whether Vegetative Garden Roofing, Photovoltaics, for the best in water integrity and expertise, rely on CRCA Members.