There are a number of choices of flat roof waterproofing systems that are available to commercial building owners. Within each product category, there are often multiple variations in how the waterproofing systems may be applied.
As a result it can be confusing for a building owner to choose the best solution for their particular requirements. Factually, most commercial building owners base their flat roof replacement purchasing decisions based on budgets either real or imagined.
The correct approach when considering any such budget is to first examine life- cycle for a particular waterproofing system which actually demonstrates best value over time. In other words; a more expensive system by initial purchase may actually prove to be less expensive over time.
A case in point is SBS modified bitumen roofing assemblies. (SBS is the acronym for styrene-butadiene-styrene). In simple terms it is a particular formulation of rolled roofing goods that is designed to withstand harsh temperature change and which is designed to have elastomeric qualities that allow it to expand and contract as a result of temperature change, thermal, and building movement.
These products are classified as synthetic rubber, constructed of thermo-plastic elastomer, polymers, and bitumen, with fiberglass reinforcement. They are known to provide durability in colder climates. Used throughout Europe for decades, and widely popular in North America for the past thirty years;SBS modified bitumen roof assemblies have proven to provide superior lifecycle over conventional BUR (Built Up Roof/ tar & gravel) systems of recent years.
Further advantages include the fact that SBS systems are lighter than conventional BUR, are thicker as a two ply assembly that four plies of organic felt, and involve producing less carcinogens when compared with burning hot asphalt in kettles.
Traditional methods of installation for SBS include open flame torch applied, hot asphalt applied, cold adhesive applied, and “peel & stick” applications. The application methodology used can be influenced by the type of structural roof deck and what the building requirements may be.
As an example; an older wood decked structure would eliminate risk of fire by using a cold applied application. Similarly; a school, hospital or health care facility would also benefit from this method due to low odour and low VOC’s.
It is therefore important for the roofing contractor and building owner to consider accommodation of building occupants, tenants, and activities being conducted within the building. Reduction of fire risk is a no brainer.
A cold applied assembly may however cost more to install initially than a torch applied system. This is due to the fact that liquid adhesive materials are necessary to complete the work. Application may also take longer if there are a number of details and protrusions on the roof.
In addition to the above factors, one may find that the cold applied assembly would last longer and have less failure risk due to over-heated seams, inconsistent heat coverage of the field membrane during application, etc. all of which would contribute to the overall longevity of the water-proofing system.
When installing an SBS roof system, the average reliable lifecycle of such a system is easily fifteen to twenty years. Many such assemblies last up to twenty-five years before requiring replacement. This assumes that such systems are being installed to manufacturer specifications.
By comparison; BUR roof assemblies constructed using modern asphalt formulation are reported to provide an average life-span of fifteen years. (Older BUR assemblies that utilized asphalt formulations pre 1977, were often known to last in excess of twenty years and often 30 years with proper maintenance).
On a cost comparison basis, and assumimg a highly competent installation of either a BUR or an SBS assembly, the building owner may conclude that although paying more for an SBS system initially, that it may outlive the BUR assembly by thirty percent on average.
When one considers a time period of fifteen to twenty years and factors in the cost of inflation over such a time; it becomes more apparent that the SBS system would be most cost effective over time.
Where BUR materials are concerned, excluding the cost of such items as thermal insulation, they are less expensive than SBS materials. Labour required to perform a BUR is higher because of the process involved.
SBS materials cost more initially, however labour costs can be lower because the installation team can be engaged in installation of the field membrane directly, as opposed to operating support equipment such as tar kettles, aggregate hoisting, mop spreaders, etc.
When it comes to SBS roofing products; each major manufacturer has developed systems which can be tailored to building usage requirements. As an example, there are white graule surfaced cap sheets which are designed to reflect the sun’s UV degradation and can help serve to lower a building’s heating and cooling costs, particularly when combined with higher levels of thermal roofing insulation. Such systems fall into the cool roofing category.
Other cool roofing products include single ply membrane assemblies like TPO, white surfaced EPDM, and PVC membranes.
“Peel and Stick” SBS membranes are essentially self adhering products which have a release film on the back, which allows technicians to easily maneuver the sheets in place, and then fold back the material to remove the protective film backing. A heavy roller is used to insure pressured adhesion.
Application of peel and stick base plies can be a tremendous time saver when dealing with flat roofs which have protrusions and obstacles in close proximity to one another. Such products allow the roofing contractor to make such areas temporarily water-tight until the cap sheet is ready to be applied.
Imagine a large factory with numerous roof top units and HVAC equipment, where completing water=proofing details around each appliance can take hours.
The self adhering SBS , while more expensive per roll; will help get the building dry under threat of rainfall, and can save back breaking hours of mopping or torching in details. Such products are also an excellent choice for completing membrane flashing details at walls, units and other finicky areas of the flat roof.
There are complete self – adhering SBS systems which include both the base sheet and the cap sheet; and are ideal for residential flat roof applications where there is a drainage grade to the roof. The system is becoming a preferred method for such jobs.
Installing SBS modified bitumen using hot asphalt application can be popular on wide open commercial roofs, permitting mass production to be accomplished. Some roofing contractors prefer a hybrid method of hot mopping the base sheet to quickly water-tight large areas; and then torch welding the cap sheet where they are concerned with finish details, as well as lessening fire risk.
The subject is a big one when it comes to modified bitumen, but luckily there are experienced flat roofers, engineers, and systems manufacturers, who are a valuable resource for the commercial / industrial / institutional property owner needing to invest in a flat roof replacement.
To learn more about commercial, industrial and institutional flat roofing , sheet metal, and other related building envelope services; visit www.avenueroadroofing.com.
