Metal Roofs, Energy and Sustainability: The Claims That Hold Up

Metal roofing gets marketed as the environmentally responsible choice, often with a percentage saving on energy bills attached. We do not quote percentages, because the honest answer depends on the house far more than on the roof. But several of the underlying claims are real, and they are worth separating from the ones that are not.

Summer heat is where the roof matters

A roof's biggest effect on energy use comes in summer. Sun on a roof heats the covering, the covering heats the attic, and the attic works its way into the rooms below.

Metal helps here in two ways. Lighter colours reflect a large share of the sunlight that would otherwise be absorbed, and metal sheds heat quickly once the sun goes off it. The colour you choose makes a real difference: a pale roof and a black one behave quite differently on a July afternoon. We go into this in do metal roofs keep a house cooler and choosing a metal roof colour.

The other half is the air gap. Panels installed on strapping leave a ventilated space between the metal and the deck, so heat that gets through the panel is carried away rather than conducted straight down. Why a metal roof needs an air gap explains how it works.

Winter is mostly about insulation

In an Ontario winter, the roof covering is not what keeps the heat in. Insulation and air sealing in the ceiling and attic do that, and a new roof of any material will not make up for a poorly insulated attic.

So if your main concern is heating bills, a metal roof is not the first place to spend. Have the attic looked at. If you are replacing the roof anyway, that is a good moment to do both, because the attic is easier to get at and you will have someone up there looking.

How long it lasts is the biggest environmental factor

The strongest sustainability argument for metal is its lifespan. A roof that does not need replacing is a roof that does not get manufactured, trucked, installed, torn off and buried again.

Asphalt shingles are a large source of construction waste, and every shingle roof eventually becomes a bin full of it. A metal roof installed over a sound deck, and on some homes installed over the existing shingles, avoids at least one of those cycles.

What happens at the end

Steel is one of the most widely recycled materials there is, and roofing steel at the end of its life has scrap value rather than a disposal cost. That is a genuine difference from asphalt, which mostly goes to landfill.

It is fair to add the other side: making steel uses a lot of energy up front. The case for metal rests on spreading that cost over a very long service life. A metal roof that has to come off early because it was badly installed loses most of that argument.

The claims to be careful with

• Precise savings figures. Any number that does not depend on your house, your attic, your colour and your orientation is a guess.
• "Cool roof" in every colour. Reflective coatings help, but a dark roof is still a dark roof.
• Winter savings from the covering alone. In this climate that is insulation's job.

If you are planning solar, metal is a good base for it, and putting solar on a metal roof covers what to plan for. If you want to talk through your own house, get in touch.