Flat Roofing

Flat roof is a common term used to describe low slope roofing systems with a slope of less than 10 degrees. Flat roofs have existed for centuries, and roofers have developed different types of coverings for these systems. In this article, we provide an overview of the most common types of roofing systems used by Atlanta Roofers today.



These are single-ply roof membranes made from thermoplastic olefin or ethylene propylene rubber. TPO membranes have “resistance to ozone, are algae-resistant, environmentally friendly and safe to install” (roofhelp.com, n. d.). The typical thickness of TPO sheets varies from 40 to 100 mils. Roofers use hot air to seal seams between sheets. TPO membranes can be almost any color but are more typical in light gray or white. Lighter shades help to reduce the temperature of the roof’s surface. The life cycle of a TPO roof is about 10 to 20 years. There are three basic types of TPO membranes: ballasted, mechanically-attached, and fully-adhered. In the first case river rocks or concrete pavers are used as ballast that holds membranes in place. The material is put on after all penetrations and edges around the perimeter are sealed. “Mechanically-attached membranes are those that use some type of special screw-type fastener to secure it. The type of fastener will depend on the type of substrate, but all fasteners are generally screw-type fasteners” (roofhelp.com, n, d,). Fully-adhered membranes are attached to the substrate with the aid of special glues.

The main advantages of TPO are flexibility, high level resistance to mechanical damage, weather impact, algae, ozone, fire, grease and chemicals. The material is installed without disruption to other building operations and, insulation such as ISO can be added under it as the part of the process. Reflective power of the white membranes helps to save costs and reduce heat loss.



Polyvinyl Chloride membrane is another type of a single-ply roof covering. Manufacturers add different plasticizers, stabilizers and other components to achieve desired features like flexibility or durability. The thickness of PVC sheets is about 45 mils to 90 mils; the most common sizes are 50 mils and 60 mils. The back surface of the product can be smooth or with the adhered nonwoven fleece layer. PVC membranes are produced in different colors, but the most common shades are white and gray. Seams are sealed with chemical welding or heat. There are the same types of PVC covering as for the TPO membranes: fully-adhered, ballasted and mechanically attached. The material should be installed on a separating layer, because plasticizers can migrate to the insulation and reduce construction’s quality.

PVC covering is a durable material with high levels of fire, chemical and wind resistance. “The American Society of Testing and Materials (ASTM) requires a minimum breaking strength of 200 pounds per inch” (roofhelp.com, n. d.). The level of fire resistance gives an opportunity to use different types of insulation under the membrane. PVC covering will not be damaged by animal fat and many other chemical substances. It is also easy to install the material.


Modified Bitumen

This is a multilayer roll covering that consists of asphalt and different modifier, which add rubber-like or plastic properties. First type of features appears with the aid of Styrene Butadiene Styrene (SBS), and plasticized features appear because of Atactic Polypropylene (APP). “Surfacings for MB membranes include aggregate surfacing, mineral surfacing, metal foil-laminate surfacing and smooth liquid-applied surfacing” (“Flat Roofing Systems”, n. d.). There are one, two and three ply Modified Bitumen roof systems. Sheets’ common widths are 36” and 39”, and they should be laid with a 3” overlap on the edges and sides. The top layer should have a granular surface to protect the covering from the ultraviolet light regardless of the system type. Installation depends up the modifier. SBS membranes are commonly put on the cold adhesive or ho asphalt. Some products are self-adhered. APP covering is typically torch-applied or heat-welded.

Modified Bitumen covering create a durable surface with high level waterproofing features. It is easy to repair the roof, and its installation is cost effective compared to other types of systems. The quality of rolls id checked during production, and it is easy to install the material.



Ethylene Propylene Diene Monomer or EPDM is a single-ply membrane made of synthetic rubber. The life cycle of covering is about 15-25 years. EPDM “is often installed for roofs that have problems with weathering, failing joints, and inflexibility” (“Flat Roofing Systems”, n. d.). Membranes are attached to the substrate with the aid of water-based or solvent-based adhesives (fully-adhered) or manufacturer-approved mechanical technology (mechanically fastened). The last type is loose-laid system, where the covering is secured only at the perimeters and penetrations. Material is held in place by ballast made of river rock or concrete pavers.

EPDM is an economically beneficial material with low installation labor costs and low maintenance requirements. It is durable and weather resistant and can be used in areas with windy environment.


Built Up Roofing (BUR)

The membrane is composed of reinforcing fabrics and bitumen. "Built-up" roof material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate (gravel or slag), emulsion or a granule-surfaced cap sheet” (roofhelp.com, n. d.). Base sheets are attached to the substrate with nails or other fasteners. Next layers are felts with cold-applied liquid adhesive, hot asphalt or coal tar. Same substances are used to install the cap sheet. The surface is covered with emulsion that can be protected from UV rays with aluminum coating. BUR roofs provide waterproof and UV protection. The surface is weather resistant and does not require high maintenance. The system has a long life cycle that depends up the amount of plies. The minimum longevity varies from 15 to 25 years for 3-ply to 5-ply systems respectively.



This type is sprayed polyurethane foam that consists of two liquid components^ isocyanate and polyol. After the mixture at a one-o-one ratio the material expands 20 to 30 times and form solid, seamless, water-resistant structure with high level thermal insulation abilities. The foam can be put on different types of substrate, except the APP modified bitumen. SPF should be covered with a protective layer that will prevent mechanical damage and UV exposure. Foam is applied by layers with thickness from 1/2” to 1”. An appropriate installation and maintenance will create a roof with life cycle more than 50 years. Foam surface is durable and can handle foot and construction traffic. Most types of mechanical damages can be repaired with simple polyurethane caulking.