Roofing

Single Ply

Single ply roofing systems are, as the name suggests, roofing systems consisting of one “ply” or “layer” or roof membrane. These systems are comprised of two families: Thermoplastics and Thermosets, each with many hybrids and evolutions.

Thermosets

Thermosets incorporate polymers that are cross linked or vulcanized. This means their properties cannot be changed and they can only be bonded with suitable adhesives. The most prevalent thermoset roofing membrane is EPDM (Ethylene Propylene Diene Monomer) which closely resembles a sheet of rubber. The seams of an EPDM roof are made using contact cement or double backed adhesive tape. Installation can be achieved by mechanically fastening, fully adhering or ballasting with stones such as river rock. These systems have been in the field for many decades and are well proven. Being a cured material they are basically inert and have a long service life.

Thermoplastics

Thermoplastics by definition can be repeatedly softened by heating and return to their normal state as they cool. This allows the seams on thermoplastic membranes to be heat welded or fused together using controlled hot air providing a permanent watertight seam. Similarly, all the detail components, such as pipe boots are welded to the surface of the membrane.

The principle types of thermoplastic membranes are PVC (Polyvinyl Chloride) and TPO (Thermoplastic Olefin). These usually come in a light or white color finish which both reflects the solar spectrum and emits heat. Know as “cool roofs” these characteristics bring them into compliance with California Building Code Title 24 part 6 designed to reduce heat entry into a building thereby reducing the air conditioning load. All single ply systems should be installed over a smooth surface. Usually this is accomplished by installing the membrane over insulation or a gypsum board faced on both sides with fiberglass. The membrane is secured to the substrate using mechanical fasteners or by fully adhering to the substrate.

Benefits: Lightweight, odorless, positively watertight seams (thermoplastic), generally white in color compliant with California title 24.
Limitations: Initial cost can be higher than BUR systems.

Built Up

BUR is the acronym for Built-Up Roofing, so called because it is field assembled using alternate layers of roofing “felt” and asphalt. It is one of the oldest systems in the modern roofing industry and provides a certain level of insurance against mechanical damage by virtue of the multiple layers. The felts themselves are not watertight and the resistance to water entry is provided by the layers of asphalt.

Previously considered the least expensive roofing system, the current rapid increase in the price of asphalt is diminishing the differential in cost between BUR and some of the Single Ply Systems. Also the requirement in California that some roofs have a reflective and heat emissive membrane has resulted in the BUR manufacturers’ producing white surfaced materials to meet this requirement. These white BUR’s are more expensive than some of the single ply membranes which have always been inherently reflective.

Benefits: Multiple layer redundancy favored by some.
Disadvantages: Typically a higher maintenance requirement than competing systems. With high asphalt costs the perceived price advantage has severely eroded.

Modified Bitumen

The words “asphalt and “bitumen” are virtually interchangeable. A modified bitumen system is very similar to a Built-Up system EXCEPT the asphalt used in these systems has been modified by the addition of synthetic rubberized polymers. The polymers provide increased resistance to brittleness in cold temperatures and increased elasticity of the sheet. Together, these properties offer a greater expected service life over their BUR “cousins”. There are two types of systems SBS (styrene-butadiene-styrene) and APP (attactic polypropylene). Each imparts a flexibility prolonging the system life. In some systems the back of the sheets are coated with the modified asphalt which when heated with propane torch melts and forms the adhesive which holds the system together. These systems are commonly referred to as “torched” systems.

Tile And Shake

Although considered residential roofing systems, many non-residential buildings employ these roofing systems, more especially tile, either completely covering the entire roof, or as an accent finishes on areas such as towers. These are often specified for “steep slope” areas of the roof such as mansards. Examples of non-residential roofs utilizing tile or shingle include buildings such as wineries and student housing.

Metal Roofing

Metal roofing systems are possibly the fastest growing segment of the non-residential roofing market. This is because metal offers a large selection of styles and colors and has a reputation for longevity. Most of the attractive metal systems seen in areas such as shopping centers are called “architectural metal systems” and require a structural supporting deck underneath the metal with a watertight underlayment.

There are also a “structural metal systems” which are attached to a metal framework and are strong enough not to require any supporting deck. The modern versions of these systems utilize hidden fasteners obviating the need to screw through the metal panels to the structure. This avoids the previous problems of rust at the screw holes which led to leaks.

BEST installs metal roof systems by many manufacturers ranging from almost flat to steep Slope. These roofs come in diverse styles such as flat and derivatives of standing seam configurations and finishes including aluminum, zinc, copper, galvalume and various Kynar type color finishes.

Foam

Polyurethane foam roofing systems (often referred to as simply Foam Roofing) are created by spraying a liquid mixture onto the roof surface where it immediately rises and hardens. The mixture is a combination of two chemicals that are mixed in the correct proportions in the spray gun head. Each pass of the spray gun produces approximately ¾” of foam thickness. The resulting foam is non-intercellular (the foam cells are not connected, therefore they do not absorb water as a sponge would), and resists damage created by foot traffic.

In the hands of a skilled applicator the foam can be contoured during the spray process to create slopes to enhance drainage. Foam is sensitive to ultra-violet light and must always be protected with a manufacturer recommended thickness of elastomeric coating.

Maintenance is usually very low and consists mainly of maintaining the integrity of the coating. – usually every 7-10 years.

Benefits: Provides insulation and roofing in one seamless assembly. Lightweight and long lasting.

Limitations: Extremely applicator sensitive.

Coating

Coating an existing roof can extend its service life, provided that the existing roof is in a salvageable condition. It can also bring a roof into compliance with Title 24 Part 6 as it applies to reflectivity and heat emissivity. Coatings can be applied to any roof surface; metal, built-up roofing, single ply, etc. A foam roof MUST be coated from day one – it is part of that roofing system and it is essential that the integrity of coating is always maintained.

Coating systems on metal roofs usually include treating the seams, and on older systems, treating the exposed fasteners prior to the application of the coating. Metal roofs especially benefit from coatings as it keeps the metal cooler and reduces expansion and contraction.

Coating a roof membrane prevents the degradation caused by UV light and keeps the roof cooler so that any membrane under the coating is fully protected which extends the service life.

Some coating systems include a fabric embedded in the coating to add tensile strength to the system, yet others under a classification called “Monoform systems” increase the tensile strength by using strands of fiberglass introduced into the coating stream as it is applied.