Commentary and Recommendations For Roof Systems

Further to our discussions, I am writing to provide some comments on various roofing systems and some recommendations for roofing systems.


The roof areas on the ‘COMPANY’ are sloped or steep roof areas as opposed to flat or low slope roof areas. The roof systems installed on steep roofs are water shedding systems typically – these system will not withstand a head of water and they function by shedding water off the building. Asphalt shingles will not keep the interior of a building dry is they are installed on a flat roof substrate unless a continuous waterproofing membrane is installed under the shingles.

Asphalt shingles have been the standard of the steep roof industry for many years. The manufacturing of asphalt shingles is well understood, the weathering characteristics of asphalt shingles are well established and the service life of each grade of asphalt shingle is predictable. The relatively recent  substitution of fibreglass reinforcement in asphalt shingles has improved the performance and longevity of asphalt shingles. The life cycle costs and the initial cost of asphalt shingles is typically lower than various other steep systems, including metal systems.

There have, as with virtually every other roof system, been some problems with asphalt shingle installations. There have been shingles manufactured with defects and there have been poorly installed shingle systems. There have been poorly designed shingle roof systems.  I always emphasize “shingle systems”, because the installation of a high quality shingle roof system is more complex than simply nailing some shingles on a building. Unfortunately, many shingle roof systems have not and are not viewed that way. Setting aside manufacturing defects, which are rare with quality manufacturers, the most problematic issues with shingle roof systems are system design and installation labour. Ventilation and substrate are included in the design.

Many, including contractors and individuals, who install asphalt shingles don’t consider the ventilation that is available in the attic areas below the shingles. Shingles are obviously exposed to sun and heat from above – if the attic spaces below are not properly ventilated, heat aging from below will occur and premature failure of the shingle will occur. The substrate must stable enough to properly support the shingles with buckling of excessive movement. The details of the a high quality asphalt shingle roof system are hugely important – metal drip edge components, proper starter strips, quality projection flashings, quality underlayments – all steep roof systems should be provided with a continuous underlayment that is fully adhered to the deck substrate, well executed valley assemblies and high quality, free flowing attic vents are all required for an shingle roof system to be long lasting and problem free. And, of course, the actual installation procedures used must be of high quality as well – the proper number and quality of nails and well installed nails – not over driven or under driven are essential if the roof system is to perform in the long term. It takes more than a hammer, a ladder and a pick-up truck to install a high quality asphalt shingle roof system.

A well designed and installed asphalt shingle roof system will keep the building interior dry for many years. It is not reasonable to reject asphalt shingles based on poor performance in some applications.

There are of course, options to asphalt shingles – virtually all are more costly – both in initial or first cost and also based on life cycle costing. Almost all provide very long term warranties on paper, at least. But a building owner is not purchasing warranty or a promise – the building owner desires a long term, well performing roof system. Warranties and salesmanship do not provide a quality roof system – the three elements of a quality roof system are excellent design, high quality materials and high quality installation labour.Let’s focus on metal roof systems with a particular emphasis on metal shingles. Metal shingles are almost always – in the case of roof replacement or re-roofing – installed over the existing roof system. This is a cost saving measure, but there is also another reason for installing over a previous roof system – particularly asphalt shingles – the metal shingles are often not able to prevent water from passing through the metal shingle assembly. There are many reasons for this – distortion due to temperature induced movement, inter locking seams and components that don’t interlock, uneven substrates, proof detailing and just plain bad installation. The existing roof below the metal shingles provides another layer to shed water from the building before it enters the interior. There is often talk of ventilation between the metal shingles and the existing roof materials, but haphazard ventilation is often worse than no ventilation at all – attic ventilation must be done with purpose and deliberation. I refer to the earlier comments about proper substrate for a high quality roof system.The fact that metal shingles are made from metal is often portrayed as a magical happenstance – metal will last virtually forever, metal is tough and so on, but much of the verbiage for metal shingles is exaggerated. Metal will last a long time if it is coated and protected from corrosion. Metal is tough if it is thick enough to resist the forces imposed on it – paper thin metal components have little toughness, even if provided with ribs and creases. Paint type coatings applied to metal shingles, even the very good quality fluoropolymer coatings, have a service life of about 20 years – after the coating weathers away the metal is vulnerable. Re-coating costs money and is very difficult logistically – the spray application of a new coating is fraught with danger, coating particles drifting from the site of application will adhere to virtually any surface – parked cars and house siding as examples. In addition, access is difficult to the higher roof areas of the building – foot traffic on light gauge metal shingles can deform the shingles and can lead to (sometimes more) water infiltration, interlocks on laps can be dislodged, fasteners loosened and exposed edges are vulnerable to wind uplift. Surface preparation is difficult – coating adhesion can be compromised and hydraulic man-lifts of sufficient reach can be difficult to manoeuver around the building.

And there is the concept of system – metal shingle roof systems are comprised of many proprietary components – the shingles themselves, end closures, valley boundary pieces, projection flashings and other accessories. Failure to install any or all of these components will lead to water infiltration. Further metal is a high movement material, particularly metal components coated with dark colour coatings – temperature induced expansion and contraction can and does wreak havoc with metal roof systems – installation defects are magnified and system details can fail. Dramatic temperature changes from, for example, 170 degrees F. on a summer day dropping to 50 degrees F. in a rain shower, can produce very sudden and destructive shrinkage of metal components. Differential movement between individual components of different size and configuration can produce failures.

Metal shingles roof system provide a three dimensional, textured appearance that can be beneficial to the look of a building, but in the case of larger roof areas, this appearance can overwhelm the visual aspects of the building and produce less a than desirable appearance. Ice and snow accumulations on the slippery surfaces of a  metal roof system can be dangerous. Ice guards at  the edges of the roof can often allow the build-up of substantial  depths of ice and snow – so substantial, in fact, that the ice guards and other projections can be sheared off when the ice and snow load shifts and falls. The ice guards themselves can often present the potential for leakage both from installation in the vulnerable eaves areas and from deformation and damage from restraining ice and snow loads. By contrast, asphalt shingle systems or other granulated roofing materials tend to “hang on” to ice and snow due to the roughness of the roof system surfacing.


Asphalt shingle roof systems of the proper design, utilizing high quality, long term fibreglass shingles, installed by a very competent contractor with good installation procedures can provide a long term, well performing roof system that will be cost effective and provide excellent life cycle costs. In addition, the eventual deterioration of an asphalt shingle roof system is predictable and allows for budgeting and replacement on a “no surprise” basis. Wintertime conditions are mitigated by the ability of granulated surface to retain ice and snow, no recoating is necessary during the lifetime of the roof system and the underlayments under the asphalt shingle roof system provide redundant waterproofing.

Metal shingle roof systems are more expensive by a substantial amount than asphalt shingle roof systems, with the associated higher life cycle costs, will require recoating – with the difficulties mentioned, present difficulties in wintertime conditions, can be damaged by foot traffic, are more difficult to install correctly and are prone to temperature induced movements that can deteriorate and compromise the system.