February 23, 2018 - Roofing
By Michael Dohar
Between a flurry of advances in polymer science, and commercial roofing companies employing PhDs and chemists to staff in-house labs, roofers and facility managers are speaking a new language. Check out these science-related terms and how they relate to commercial roofing:
• Elongation and tensile strength are two fundamental, critical factors that core samples are tested for. A core sample is a drilled-out, cylindrical section of the roof that shows the various layers of the roof system, including the membrane, insulation, etc. Elongation refers to the amount of extension of an object under stress. It's usually expressed as a percentage of its ability to be stretched or pulled without breaking compared to its original length. Tensile strength is the resistance of a material to breaking under pressure.
With any building, there will be natural shifting and moving. Along with the actual building moving, there will be expansion and contraction of the roof due to variation in temperature. Because of this movement, the roof must be able to stretch sufficiently to compensate for any expansion (elongation), while also being "tough" enough to resist any splitting (tensile strength).
• Puncture resistance is a measurement of the relative ability of a material or object to inhibit the intrusion of a foreign object. It's not uncommon for roofs to be subject to a barrage of flying debris during times of high winds or damaging hail. Puncture resistance tells us to what degree a particular material can withstand such elements.
• Permeance is the state or quality of a material or membrane that causes it to allow liquids or gases to pass through it. This comes into play specifically with the waterproofing characteristics of materials used in roofing.
• Adhesion refers to the action or process of adhering to a surface or object. When we talk about adhesion in roofing it typically deals with a material's ability to withstand wind uplift, or, over time, to maintain an effective seal against the decking and strength in the seams of the membrane and flashings to provide adequate waterproofing. Adhesion also helps with building movement.
• UV resistance is the ability of a material to resist ultraviolet (UV) light, or sunlight. UV rays will cause non-resistant materials to fade or discolor, creating premature wear and potential for failure. UV light also causes oxidation of materials, breaking them down to the point of failure. In other words, it's more than fading and discoloration.
• Swelling refers to the expansion of a material or membrane after the introduction of water. Swelling can be detrimental to an elastomeric roof coating because it signifies absorption of water into the coating. The absorption of water can lead to loss of adhesion and compromise the waterproofing on the roof.
• Breaking strength is the greatest stress or tension that a material is capable of withstanding without rupture.
• Oxidation is the process of a chemical compound losing electrons via UV light. As a material oxidizes, it loses strength and becomes susceptible to failure. Reference UV above.
• Lamination is the technique of manufacturing a material in multiple layers. Laminates are permanently assembled using heat, pressure, welding, or adhesives. Once a laminated surface is penetrated or cracked, it becomes highly susceptible to failure, or de-lamination.
• Saturation is the state or process that occurs when no more of something can be absorbed, combined with, or added. Saturated roof membranes contain structural and waterproofing reinforcement evenly through all layers.
• Polymer degradation is a change in the properties — tensile strength, color, shape, etc. — of a polymer or polymer-based product under the influence of one or more environmental factors, such as heat, light, or chemicals, usually by way of sunlight or oxidation.
• Plasticizers are substances, usually solvents, added to a synthetic resin to produce or promote plasticity and flexibility, and to reduce brittleness. Plasticizers are used in single-ply roofing membranes to impart desired physical properties to the membranes. Plasticizers make membranes less brittle and therefore have better elasticity. UV exposure, however, can cause the plasticizer to leach out and cause the membrane to crack.
• Viscosity is a material characteristic expressing the magnitude of internal friction, or the resistance of a fluid to flow. More commonly it's a liquid's thickness, i.e., the pourability of water versus a maple syrup consistency. It's commonly used in roofing in relation to liquid-applied materials.
• Percent solids refers to the percentage mass of solid material present in a liquid or semi-liquid sample. Coatings are compounded using various liquids and solids. In general, a coating with a high percentage of solids will perform better as a waterproofing agent.
• Specific gravity is the ratio of the density of a substance to the density of a standard - usually water for a liquid or solid, or air for a gas. Similar to percent solids, a coating with a high specific gravity will be a denser coating and therefore a better waterproofing material.
• Reflectivity is the property of reflecting light or radiation, especially reflectance as measured independently of the thickness of a material. In roofing, reflectivity is used in relation to the ability of the roof to redirect sunlight, maintaining a cool surface, and keep it from being absorbed as heat, which can cause premature wear.
• Emissivity is the ratio of the energy radiated from a material's surface to that radiated from a blackbody (a perfect emitter) at the same temperature and wavelength, and under the same viewing conditions. The emittance of a material refers to its ability to release absorbed heat. Scientists use a number between 0 and 1, or 0 percent and 100 percent, to express emittance. With the exception of a metallic surface, most roofing materials can have emittance values above 0.85 (85 percent).
One example is a metal wrench left in the sun, which is hot to the touch because it has a low emissivity value.
• Solar reflectance is the most important characteristic of a roof product in terms of yielding the highest energy savings during warmer months. The higher the solar reflective value the more efficient the product is in reflecting sunlight and heat away from the building and reducing roof temperature.
We're in the midst of a boom in innovative commercial roofing technology that's resulting in better-performing, longer-lasting materials. Keeping up-to-date on how roofing companies are testing, researching, and developing materials can benefit facility managers by making them more knowledgeable purchasers and managers of roofing services.
Michael Dohar is the chief operating officer of Simon Roofing, a national commercial roofing installer/manufacturer that's among the largest roofing contractors in the United States.
