Commercial and industrial property owners and facility managers have a number of system options to consider when having to confront the replacement of their flat roofs.
Historically; BUR (built-up roofing, often termed tar and gravel roofing) had been the most popular choice of flat roofing system for over 100 years in Eastern North America. In the 1980’s, a large segment of the market chose two-ply, modified bitumen as the popular alternative; largely due to it’s lighter weight characteristics and high tensile strength.
Both of these systems are largely petroleum asphalt-based products.
Fast forward to the past twenty years; where single-ply flat roofing technology has become the fastest-growing segment of the commercial flat roofing market. This is for a variety of reasons to be discussed. Also important to know, is that many single-ply systems have been in existence and widely used in Europe for well over a decade beyond that time period.
First to understand are the types of single-ply systems that are available. The three major types are EPDM, PVC, and TPO. The acronyms stand for Ethel-Propylene-Dienne Monomer (EPDM), Polyvinyl Chloride (PVC), and Thermo-Plastic Poly-Olefin (TPO).
Each of the systems has their own merits, and in many regards could be considered similar in nature in the context that they are typically less labour intensive to install, and that they share the concept of larger membrane sheets, therefore minimizing the number of seams in the finished assembly.
Where they differ, is in the material and chemical composition for each individual product type, and slight variations in terms of the methods of installation, and the securing of overlapping material seams.
For the purpose of this conversation, we will discuss TPO single-ply membrane systems as it represents the fastest-growing type of single-ply technology being used today.
A subject of great discussion these days, and important to many people who are concerned about the environment; are the use of products which provide advantages in terms of using less fossil fuels, are recyclable in nature, and help reduce our carbon footprint.
Cities in North America such as Chicago; were leaders in the effort to curb the Urban Heat Island Effect. The objective being to lower the ambient temperature of cities which resulted from radiating heat coming from asphalt covered rooftops and pavement surfaces.
The adoption of cool roofing technology, such as mandating TPO white roofs and green roofing assemblies; proved to be successful in this regard. In Canada, Toronto has championed the cause, having passed a bylaw a few years ago, requiring new commercial development to use such roofing technology, and also providing incentives to commercial and industrial building owners that intend to retro-fit their flat roofs with new TPO cool roofs.
In Toronto, commercial building owners can apply to The City for the ECO-Incentive Grant, which provides $5/sq. meter, to a maximum of $50,000 for the retrofit of such roofs.
Related Content: Six Toronto Commercial Roofing Tips For New Building Owners
Summary Advantages of TPO Membrane Roofs include:
- Having a white reflective surface which serves to lower heating and cooling costs, further enhanced when combined with increased levels of thermal roof insulation, incorporated into the roof assembly.
- TPO is fully recyclable at the end of the products life-span.
- TPO typically involves less seams which minimise failure points.
- The membrane is highly puncture resistant.
- Overlapping material seams are hot-air welded. The seam strength is even tougher than the membrane itself.
- TPO does not involve the use of open flames or odorous hot asphalt.
- TPO is easy to repair when required.
- Manufacturer warranties are available for 20 years.
- TPO membranes are lighter than conventional asphalt based roofing systems and require no ballast.
- On wide open roofs, labour savings are considerable.
- Although roofing manufacturers do not advocate flat roofs that hold water for extensive periods of time; TPO has the ability to withstand saturation over the long term due to it’s chemical formulation and membrane construction qualities.
- Using TPO can increase the load capability that a flat roof can sustain based on the fact that it is lighter weight than many competing assemblies.
TPO Roof Systems can be installed in three different methods. Loose laid, fully adhered, and self-adhering versions.
When flat roofs are being replaced; those that have multiple layers of existing roofing systems, and those that have exhibited considerable water ingress over time, should be removed to expose the bare substrate.
Some flat roofs can be “skinned”; involving the removal of existing gravel or ballast, removal of the waterproofing layer and exposing the thermal insulation already within the prior roof assembly. If the insulation is dry and has been installed correctly; such insulation can be re-used resulting in large cost savings for the building owner.
In some instances; if an older flat roof has not exhibited leaking, and there is a single roof assembly; gravel can be removed to reduce weight, and the new TPO assembly can be installed on top of a cover-board type of insulation. This method can be viable in some circumstances, without compromising the existing load capability of the roof.
Determination of the correct approach for re-roofing is determined by performing test cuts, and or thermographic imaging. An experienced flat roofing contractor can then prescribe the best approach or options, based on the actual condition of the existing assembly.
As an example; although a flat roof may appear a good candidate for recovering; if there was an absence of sufficient thermal insulation (Such as fiberboard insulation being present), and or evidence of an insufficient vapour retarder beneath; a complete strip off and replacement may be the best solution for the client in the long run.
The ability to add increased thermal roof insulation can result in substantial savings for the building owner in terms of heating and cooling costs, especially over time. Often federal or provincial grants are also available to incentivize building owners to reduce their carbon footprint, resulting in additional meaningful savings.
When retrofitting TPO roof assemblies, the most common method of installation involves the loose laid approach.
In basic terms; roofs that have a large field area may be better served by this method, and where there exist considerable temperature changes, resulting in the thermal expansion and contraction of the roof assembly. One of TPO’s inherent qualities is that it can stretch and relax with building movement.
Essentially; large field panels of TPO sheet are mechanically attached using plates and screws, installed at a prescribed rate and attachment pattern, to accommodate wind up-lift standards required by the manufacturer and or building code. These mechanical fasteners which are located at the seam areas of the field sheets , are then overlapped at the seam by the adjoining sheet. The seams are robotically welded using a mobile machine. The machine is set to maintain a constant temperature, and deliver a consistent thermal weld; essentially fusing the seams of the material sheets together.
Smaller seam details around roof protrusions are completed using handheld heat welding tools known as Leister ™guns. Perimeters of the flat roof area are “picture framed” using TPO field sheets. Areas such as parapet and wall details; receive TPO membrane which is fully adhered to using special adhesive supplied by the manufacturer.
Fully adhered systems are suited to concrete substrates and smaller roof areas. The fundamental difference between loose laid and fully adhered systems is that the field sheets are fully bonded to the protective insulation boards placed beneath.
Newer versions of TPO from particular manufacturers, involve a “peel and stick” installation approach.
The material sheets are set in place, folded back, and then a “relief” film is peeled off in order to allow the membrane to be smoothed into place and caused to bond with the insulation layer beneath.
TPO roofing membranes come in three thickness.40 mil (Typically used at walls and penetrations), 60 mil and 80 mil). There are a handful of TPO manufacturers world-wide. Firestone™ is the largest provider of TPO membranes; holding the world’s record for the largest TPO roof installed in the world.
When selecting a TPO system; a building owner is wise to select a factory-certified installation contractor for the particular product type. AVENUE ROAD ROOFING® is a Firestone™ Certified Red Shield Applicator for the GTA and Ontario commercial roofing markets.
To learn more about TPO commercial flat roof systems or commercial and industrial roofing visit: