EPDM - Built Up Roofing System - Modified Bitumen - Trocal - Exposed Fastener Metal Roofs - TPO - Sprayed Polyurethane Foam - Shingles

Roofing System Life Cycle Descriptions

EPDM (ethylene, propylene, diene monomer) is rubbery, petroleum based, single ply roofing product that is constantly curing, or moving plasticizer to the outer edge of the material to keep it pliable. Once all of the plasticizer is evaporated, the membrane becomes brittle, shrinks, weakens and loses its elasticity. Additionally, EPDM is seamed on the roof with either liquid adhesive or seam tape. Exposure to water will eventually erode the seams so great care must be taken keep them dry. As the membrane cures, it becomes increasingly difficult and eventually impossible to repair.

Built Up Roofing System (BUR) is petroleum based roofing system where mastics are heated to a liquid state and applied to felts rolled out on the roof substrate. Multiple layers are laid until the system is built up to the desired thickness. Any petroleum based roofing system is constantly curing, which means it moves plasticizer to the outside layers to keep from becoming brittle and shrinking. Exposure to ponding water and UV radiation accelerate this process. In BUR, when the plasticizer is used up, the layers begin to delaminate; the system shrinks and cracks and blisters form.

Modified Bitumen (MOD) is very similar to BUR, in that, it is petroleum based roofing system where mastics are heated to a liquid state and applied to felts. But this process takes place in the factory where the roofing is then bundled into 3’ wide rolls that are either mopped or torched down onto the roof substrate. Any petroleum based roofing system is constantly curing, which means the solvents that keep it pliable are constantly evaporating. Exposure to ponding water and UV radiation accelerate this process. In MOD, when the solvents are evaporated off, the layers begin to delaminate; the system shrinks cracks and blisters.

Trocal is a PVC based single ply roofing system that was popular in the late 80’s and early 90’s but proved costly when it began to fail prematurely due to plasticizer loss. In its most basic state, PVC will become brittle when exposed to ultraviolet light. This phenomenon is counteracted by the use of plasticizers and UV stabilizers. Unfortunately, the stabilizers and plasticizers that were used in the Trocal product were not stable and often quickly evaporated off leaving the membrane vulnerable. Once the plasticizer was evaporated off, the membrane would become brittle and shrink. As it becomes tighter it will pull on the edge detail and pull itself off the edge of the building or fail under its own force and shatter like a sheet of glass.

Exposed Fastener Metal Roofs are typically found on pre-engineered metal buildings. In this configuration, the metal acts as the waterproofing layer and is fastened to the purlins with exposed fasteners. With variation in temperature, the roof panels can expand and contract up to 3/8” which puts a tremendous amount of pressure on the exposed fasteners. In addition to the thermal movement, metal buildings flex and move a great deal due to wind and air pressure as well as internal forces. As the panels work back and forth, they cause the fasteners to loosen. Also, the neoprene washer rots out in about 7 years.

An area of concern with this type of roof is the severe ice build up that typically forms on the building edge in the winter. On this type of building, a great deal of heat escapes through the roof because of the building’s insufficient insulation. Typically, a thin layer of fiberglass is draped over the purlins and under the metal roofing. Considering this configuration compacts the insulation over each purlin, it provides an effective R-value of less than 5.

As the heat escapes through the decking, it melts the snow that has accumulated on the roof. The snow melt runs down the roof to the eve which is outside the exterior wall and therefore below freezing. The water freezes and creates an ice dam which continues to grow. As water builds up behind the ice dam, it begins to flow into the fastener holes and through the gaps created between the panels by cracked and missing mastic. With this configuration, internal condensation is also a concern because the metal deck is much colder than the internal air. As the warm moist air rises it condenses on the under side of the deck, collects and drips into the insulation and room below.

TPO (Thermoplastic polyolefin) roofing membrane is a wax based heat weldable single ply product that is relatively new to the market. It was first used in roofing in 1989 and was plagued by catastrophic failures. Manufacturers scrambled to modify their formulations in an attempt to remedy the situation but many premature failures continue to plague this roofing type to this day. When installing TPO, it is extremely difficult to weld two pieces together. Even if there appears to be a proper weld, it can pull apart after one or two cold/warm weather cycles. TPO also suffers from severe expansion and contraction. The material can move from flat and tight to severely wrinkled in minutes depending on the amount of sunlight is hitting it at any given time. The movement can cause the seams and penetration flashings to fail years before they are supposed to.

Sprayed Polyurethane Foam (SPF) is applied as a liquid using plural-component spray equipment to fill cracks and crevices. It then expands approximately 30 times its original liquid volume to form a hard, closed cell monolithic roof surface. The Polyurethane Foam dries within seconds after applied to the roof surface. Its expansion is supposed to result in a weather tight roofing membrane that is fully adhered to the substrate. However, our experience has found that the expansion and contraction causes the material to pull away from walls and penetrations after a very short time. SPF requires protection from the sun's ultra-violet radiation, moisture and foot traffic. Once the SPF has been applied to the proper thickness and finish specifications, a protective layer of elastomeric coating, or gravel is applied. This protective layer is supposed to produce a durable weather resistant surface and that can be walked on for normal maintenance.

There are several inherent problems with SPF that typically manifest themselves very quickly on a typical roof. The entire process requires a perfectly prepared roofing surface, if there is any moisture at all, a large blister can quickly develop. The coating must be replaced typically at least every five years at great cost to the building owner. Even with re-coatings, the coating is easily punctured by nesting birds, foot traffic, building movement, expansion and contraction, etc. Water enters the system and causes the system to blister and pull away from the roof deck. The foam soaks up the water and holds it against the roof deck causing metal decks to rust and wood to rot at a greatly accelerated rate.

Shingles: Most premature shingle problems are a typically a result of one of two shortcomings: First the substrate was not properly waterproofed prior to the installation of the shingles. It is necessary to make the structure watertight by installing the appropriate ice and water shield and titanium underlayment along with all flashings prior to the installation of any shingle. The second shortcoming is the us of three tab shingles. With three tab shingles, there are four areas on each shingle where wind can catch the edge and cause it to lift and eventually curl. Because of this pressure, they tend to crack from gusset to gusset. Also, below each gusset, and where any shingle is broken off, there is only one layer of asphalt. Dimensional shingles on the other hand seal at the entire edge of each shingle. The shingle is constructed with a minimum of two layers of asphalt but there are three layers in most areas.