Metal roofing -how to choose

Various roof failures, including asphalt shingle blow-off, and premature curling and cracking, has led homeowners to look for more reliable and durable solutions.  As such, people often start asking about metal roofing.

Metal roofing continues to be more and more popular, despite its initial cost, because people are getting tired of having roofs that fail much before their warranties expire.  The metal product offerings come in a dizzying variety of materials, appearances, textures, colours, and performance.  How does one wade through all the sales claims and marketing hype to decide which options are truly the best for you?  It helps to remember that there is no product invented by humans that is truly perfect in every circumstance.  So the exercise is to find the product whose weaknesses are minimized in your particular circumstances, and whose strong points are fully delivered.  It should not be a surprise that proper preparation and installation play a very big role in the final quality of the result.  So let’s examine a selection of products and discuss how their weak (and strong) points should be considered in your selection process.

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Some myths about roofing

Most people think they have a good grasp of how roofs work – the shingles (usually asphalt) keep the water out, and that they do that by being the waterproof layer that stops water from getting in.  That’s more myth than fact.

Another myth, is that caulking is an acceptable way to achieve waterproofing.

Another myth, is that if you have ice-and-water shield on your roof, you’re good.

What all these myths have in common is that they misunderstand how a sloped roof system works in reality.

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Which products are suitable for DIY roofing?

The two most common materials for DIY roofing are asphalt shingles and steel panels.

Asphalt shingles are pretty easy to install – as long as you follow the instructions on the package, nail in the right place, ensure the right off-set, and install the appropriate flashings (usually NOT described on the shingle package).  Of course, in addition to the shingles, you need to think about the underlayment, the waterproofing, allow enough heat on the roof to “seal” the shingles to each other, and as mentioned before, use an appropriate flashing for each roof termination or join.  People get the shingle nailing part ok, but often forget the rest of the details (those are not described on the shingle package).  Steeper slopes or windy areas require additional measures that are usually skipped.  In addition, the shingles aren’t going to last very long – we often replace roofs that are anywhere from 10-15 years old.

Metal roofing CAN be relatively straightforward to install, if the roof is not too steep and is not complicated with valleys and skylights, and similar features.  However, there are different systems, and each system has its own peculiarities.  Let’s start with a sampling of products, and see what aspects you need to consider.

The cheapest and simplest roofing to install are steel panels such as you see often on barns and sheds.  These are sold through hardware stores, and are usually called “screw-through” roofing, because they are fastened to the deck using screws that go through the metal.  Some manufacturers require strapping under the metal panels, others don’t.  They feature relatively shallow ribs that run down the vertical direction of the panels.  Flashing details tend to be rather rudimentary, and rely on caulking for waterproofing and foam blocking to prevent insects from entering under the roofing panels.  Since they are designed to be cheap, the paint quality used on them is not very ultraviolet (UV) resistant, and often fades or bleaches in 15-20 years.  The zinc coating tends to be thin and you can see these types of panels rusting from the ends in as little as ten years.  The screws seal against moisture entry using a rubber or neoprene collar or washer, but these are also affected by UV and lose their sealing ability after 10 years or so.  For these reasons, I am not a fan of this type of product.  Depending on the thickness of the metal, some panels show the effects of snow after a few seasons, in the form of deformations or indentations in the metal between the furring strips.  These panels are better than asphalt shingles, but not by very much.  By the time the panels get to be 20-30 years old, they are usually replaced because of the poor appearance, or the rust, or the leakage at the screw-holes.  On the plus side, they are a cheap and fast way to cover a barn or shed.

A much better system is one using locking panels which have standing ribs with the fasteners hidden under the overlapping panels.  These also use various ways of locking panels to the trim and flashings, so that there are no exposed edges.  However, because these panels require bending to make the locking parts, they usually require specialized tooling for cutting and bending.  Some homeowners have the ability to do this level of work, but for most, this level of technical execution is reaching the limits of their ability.  Consider also that if your roof requires panels in excess of 20 ft., it becomes quite physically challenging to lift such a panel onto the roof and position it correctly.  Therefore, although hidden-fastener vertical steel panels are a much better choice compared to the barn roofing described earlier, both the skill level and the tooling required make it more difficult for the DIY installer.

A much easier product for DIY installation is the metal shingle.  These come in several forms and materials – steel, aluminum, copper, zinc, and stainless steel.  The surface finish can be natural, galvanized, painted, or granulated.  The shapes can be square, rectangular or diamond-shaped, and can feature various surface textures or profiles (wood grain, smooth, slate, shake, or stone).  The most common products of this type are painted steel shingles, and painted aluminum shingles.  The shingles vary in size from relatively small rectangles (9” high x 18” wide exposure) to much larger ones (18” high x36” wide).  While the details vary from system to system, in general they all rely on a system of flashings for every roof joint and protrusion.  These flashing form the foundation for the systems, with the shingles effectively just filling in the space between the flashings.  So with these systems, the emphasis is not on the roof covering (that’s the easy part), but on the correct choice, placement, and positioning of the various flashing elements.

The role of the flashings is actually quite complex.  Depending on the flashing type, they provide a hidden water channel to drain rainwater away, and/or they provide barriers to water entry, and/or they provide a secure attachment point for the shingles, and/or they are the primary means to resist wind uplift, and/or they provide a safe channel for sliding snow or ice, and of course, they have to look good.  Therefore, up to 50% of the effort on a metal roof is associated with the installation of the flashings.  The problem however, is that most suppliers of DIY materials don’t do a very good job explaining which flashings are used where, what are the safeguards you’re supposed to use, and how to ensure that the flashings are properly installed.

Of course, it is also not a good thing to install the flashings first, and then install the shingles – this approach ends up directing any water in the flashings under the shingles.  So part of the installation process is the interleaving of shingles and flashings to direct the water to the outside.  Again, this is almost never explained by the vendors of DIY roofing, and yet it is a critical component of a well-designed system.

The easiest product to install for the DIY roofer is usually the aluminum shingle.  They are relatively small,  very light, and the metal is easy to cut and bend.  Since aluminum doesn’t rust, that means the product will last a very long time.  With the right paint system on the surface, a good appearance should last 20-30 years or more, and the shingles themselves will easily last over 100 years.  However, since the shingles are made from a very thin metal, the roof preparation becomes very important to get a smooth, strong, waterproof surface that can provide proper support for the shingles.  Painted steel shingles are somewhat harder to work with, as the metal is much stiffer, so both cutting and bending is more difficult.  Granulated steel shingles are usually NOT a DIY project as they require special cutting and bending tools which are designed to cope with the granulated coating.

Because metal roofs made from shingles and flashings have many potential entry points for water (every joint is a potential entry point), it is important to understand the principles and techniques that minimize these entry points.  Furthermore, a prudent installer considers additional lines of defence against water infiltration in the form of waterproofing membranes at all penetrations and other potential leak points.  If the surface is slippery, thought must also be given to how the snow and ice will behave on the roof, and whether there are any obstructions that can catch ice and snow.

Therefore, for DIY permanent roof installation, the most common material used is the aluminum shingle system, followed by the hidden fastener vertical steel panel.  However, the two keys to a successful installation is a proper match of the materials used to the roof and to the skills of the installer, and the proper roof preparation that minimizes the potential issues.  We’ve worked with over 80 homeowners all over North America who have done this successfully.  Contact me to find out how to join this happy group.

(c) 2014 Paul Grizenko