Roofing Systems Defined

Roofing systems are generally divided into two generic classifications: low slope and steep slope. This month The Roofline will focus on the five classifications of low-slope roofing. (Source: National Roofing Contractors Association)

Low-slope roofing includes water impermeable, or weatherproof, type of roof membranes installed on slopes less than or equal to 3:12 (14 degrees). Most low-slope roof membranes have three principal components: the most important component is the weatherproofing layer or layers; reinforcement to add strength, puncture resistance and dimensional stability; and surfacing to protect the first two components from sunlight and weather.

The five classifications of low-slope roofing are:

Built-up roof (BUR) membranes are composed of alternating layers of bitumen, typically asphalt, coal tar or cold-applied adhesive, and reinforcing fabrics also called roofing felts or ply sheets.

Surfacings for BUR systems include aggregate, glass-fiber or mineral surfaced cap sheets, hot asphalt mopped over the entire surface, aluminum coatings or elastomeric coatings.

Structural metal panel roof systems are used on low-slope roofs because of their hydrostatic or water barrier characteristics. Most are designed to resist the passage of water at laps and other joints as sealants or anti-capillary designs can be used in the seams and they possess strength characteristics that allow them to span supporting members

Structural metal panel roof systems are installed over either a continuous or closely spaced decking providing solid support or one that is composed of spaced structural supports where the metal panels must span between supports.

Polymer-modified bitumen (MB) sheet membranes are composed of reinforcing fabrics that serve as carriers for the hot polymer-modified bitumen as it is manufactured into a roll material. MB roof system membranes are composed of multiple layers, much like BUR membranes, and are typically installed as a two-ply system and almost always are fully adhered.

Single-ply membranes are factory-manufactured sheet membranes. They generally are categorized as either thermoplastic (TPO or PVC) or thermoset (EPDM). Thermoplastic materials can be repeatedly softened when heated and hardened when cooled where as thermoset materials solidify, or “set,” irreversibly after heating.

The membranes may contain reinforcement layers. Common reinforcements for single-ply membranes include polyester fabrics or scrims, glass fiber, or a felt or fleece backing.

Single-ply membranes can be installed fully adhered, mechanically attached or held down with ballast. Most single-ply roof systems do not receive surfacings. 

Spray polyurethane foam-based (SPF) roof systems are constructed by mixing and spraying a two-component liquid that forms the base of an adhered roof system. The first component is a rigid, closed cell, spray polyurethane foam insulation composed of isocyanate and polyol.

The second component, the protective surfacing, is typically a spray applied elastomeric coating or a membrane, such as a fleece backed thermoset single-ply membrane. The surfacing is applied to provide weatherproofing, protect the foam from UV exposure, provide protection from mechanical damage and assist with the fire-resistance characteristics of the roof system.

Whether you’re in need of roofing repairs, maintenance or replacement, Jottan has the experts that you want on your roof. Contact us at (800) 364-4234


What to Look for in a Written Proposal

So you’ve done your homework on contractor qualifications, May issue of The Roofline, and have selected the contractors whom you feel are best qualified to present you with their roofing proposals. Once you have the proposals in hand what do you look for in each? How can you be sure that you’re comparing apples to apples?

According to the National Roofing Contractors Association (NRCA) you should look for clearly written proposals that are detailed and broken down into separate line items. This is a good sign that the contractor is being thorough and has prepared an accurate estimate.

The NRCA offers the following as a partial list of items your estimate or proposal should include:

  • The type of roof covering, manufacturer and color
  • Materials to be included in the work, e.g., underlayment, ice dam protection membrane
  • Scope of work to be done
    • Removal or replacement of existing roof
    • Flashing work, e.g., existing flashings to be replaced or re-used, adding new flashing, flashing metal type
    • Ventilation work, e.g., adding new vents
  • Who is responsible for repairing/replacing exterior landscape or interior finishes that are damaged during the course of the work
  • Installation method
  • Approximate starting and completion dates
  • Payment procedures
  • Length of warranty and what is covered, e.g., workmanship, water leakage

The above is offered as a reference. Need more information? Ask questions. As consumers, they help to ascertain the information that is needed in order to make an informed decision.