Metal roofing – the green solution for your house.  Or is it?

Compared to (most) asphalt shingle roofs, (most) metal roofs last much longer and perform much better, as long as they are properly installed.

Metal roofs are considered to be more ecological than asphalt roofs, as their longevity usually means that the metal roof is the last roof the home will need.  This longevity also means that fewer manufacturing resources are needed to produce this roof, compared to the resources needed for asphalt shingles over the life of the house.

However, this longevity of product may not be enjoyed by the homeowners, if the installation was not properly done.  Even if the installers followed the manufacturer’s recommended installation practice, a roof may fail prematurely IF the roof covering was not properly integrated with the rest of the house structure.

So let’s look at what “should” be taken into account when considering a roofing solution.

The roof covering (the metal or asphalt roof covering) is only part of a roof system, which comprises:

  • The vapour barrier
  • The insulation (type, thickness, completeness of coverage)
  • The ventilation (intake, air channel, outlet, air flow balance)
  • The roof support structure (rafters, beams, etc.)
  • The roof deck
  • The roof geometry
  • The roof penetrations and related hardware
  • The underlayment and waterproofing
  • The eavestroughs and water-channelling system
  • and the roof covering (with related flashings, fittings, etc.)

Although the roof covering gets the attention, it is the various elements of the roof system working together as a whole, that will determine the performance you can expect from it.  This means that changing the roof covering is only one aspect of ensuring that the roof performs its job correctly.  Unfortunately most salesmen selling roofing products do not have a very deep understanding of how the various elements interact, and therefore do not give the homeowner a quotation that reflects the work needed to truly integrate the covering with the structure and form of any particular roof.

For example, a very common complaint of homeowners in our climate (Monteal, Canada but also more generally applicable to the North-East of North America), is the formation of ice dams that contribute to leakages.  The “solution” often proposed is the installation of a metal roof which, according to the salesman, will allow the snow to slide off, and eliminate the ice damming.  While that is true, it doesn’t tell the full story.  The effectiveness of this “solution” depends on the roof geometry, the location of entries to the home, the additional work done on insulation and ventilation, and the protection installed to prevent dangerous snow avalanches in sensitive areas.  The “solution” can cause more problems than it solves IF it was not properly designed for the particular structure and its environment.

In the above scenario, the underlying cause is the lack of sufficient insulation, probably compounded by poor ventilation.  Solving THAT particular problem will also take care of the ice-damming issue.  At the same time, by reducing the heat lost through the attic and roof, this approach is actually a “green” solution.

Another common approach to installing a “green” metal roof, is to install the new roof over the existing roof.  According to the salesman, this approach is green because it avoids the cost and mess of a roof tear-off, adds “additional insulation”, and prevents “more landfill debris”.  In fact, the only “green” visible in this scenario is the additional money that the company will make by not doing the necessary work, and thereby doing the job much faster.  When grocery stores do this trick with expired meat (by rewrapping and relabeling the package), this is known as fraud and is seen as dangerous.  The deficiencies of this approach to the homeowner will become apparent later, and include:

  • additional weight to the roof structure (because there are now at least two roof coverings)
  • any roof deck deterioration continues to be there, but is now hidden under two roof coverings
  • waterproofing membrane cannot be installed over the old roof (since the membrane needs to be adhered directly to the deck), so the “new” roof assembly is less protected against water infiltration,
  • the old roof covering becomes a water sponge if a leak does occur, and will make it much harder to determine the true source of the leak without disassemblying the new roof
  • roof penetrations are usually sealed only with caulking (which can fail in as little as five years), instead of being properly waterproofed and sealed from the deck up.
  • The addition of outlet vents in no way replaces a proper evaluation of the insulation/ventilation behavior of the roof, and may actually reduce the performance of the roof system, if the evaluation was not properly done.

To make a metal roof installation a “green” installation, it will need both longevity and performance.  The performance comes from HOW the product is married to the existing structure, and the repair or amelioration of deficiencies that may exist.  To get a “green” roof, the roof system needs to be properly assessed, the deficiencies found and corrected, the preparation of the roof be properly done, and the roof covering be installed with all the additional safeguards in place.  Then you will have both the longevity AND the performance that you should expect.

To summarize:  To get a “green” roof the following should occur:

  1. The product used should be long-lasting (with a track record of performance and durability),
  2. At a minimum, the product should be installed following the manufacturer’s instructions AND current best practices (which are location-specific).
  3. The roof system should be assessed to ensure that deficiencies are fully identified, and that appropriate actions are taken to minimize or eliminate the deficiencies. This means that a full inspection (both interior and exterior) be done, the insulation and ventilation capacities are measured and compared to the required standards, and observed deficiencies are discussed with the homeowners.
  4. The roof (with very few exceptions) should be stripped to the deck.
  5. The corrective actions identified in #3 above, be performed.
  6. The appropriate layering of waterproofing, flashing and sealing be carried out to counter the usual modes of roofing failure.
  7. If the deficiency correction cannot be done (for budgetary or technical reasons), then appropriate measures be designed to minimize the damage that could be caused by those deficiencies.
  8. The “green” marketing claims can be verified by incorporation of specific features (of either product or installation) that deliver the performance claimed.

If you are interested in a “green” roof, but are not sure of exactly how the proposals you receive from roofers will deliver on their promises, maybe you would like to contact me and discuss the quotations.  I perform this consulting service for a fee, in the greater Montreal area.


Notes and other remarks.

In the above post, I refer to “salesman” and “salesmen” as the majority of people doing roofing sales are male.  I would love it if more women considered entering this field, but in the 20-years or so that I’ve been in this field, I met only a few saleswomen, and they were usually the wives or girlfriends of the male contractors.

Would you like to share your thoughts on the topic?

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s