Aluminum Roofing R-Value and Energy Efficiency in New England

Does an aluminum roof have an R-value?

An aluminum roof has almost no R-value of its own. R-value measures resistance to heat flow, and a thin sheet of metal conducts heat readily rather than resisting it. The same is broadly true of asphalt shingles, slate and most other roof coverings. In a house, R-value comes from insulation: fiberglass, cellulose, mineral wool or foam in the attic floor or the roof slopes. Rigid insulation boards placed above the deck add R-value too, but they are an insulation layer, not the roofing. So when someone asks how much an aluminum roof will insulate a home, the honest answer is very little by itself. Its energy effect comes from how it handles sunlight and from the insulation and ventilation work done with it. We avoid quoting energy-savings figures, because results depend on the house, the attic and how it is heated.

How does an aluminum roof save energy, then?

An aluminum roof saves energy mainly by reflecting part of the summer sun instead of absorbing it, which reduces heat flowing into the attic. Lighter and specially formulated finishes reflect more; darker colors reflect less. That summer benefit is real on hot, humid New England days, especially for upstairs bedrooms under the roof and for homes with ducts or air handlers in the attic. It can also help a top-floor apartment in a triple-decker that bakes in July. The second source of savings is indirect. A re-roof is the natural moment to fix what is underneath: add attic insulation, seal air leaks around chimneys, plumbing stacks and light fixtures, and correct ventilation. Those changes usually matter more to annual energy use than the roofing material does. Check Mass Save or your state energy office for current insulation programs.

Does a reflective roof cost me heat in winter?

A reflective roof has little effect on winter heating in most New England homes, because the attic is meant to be cold. In a well-built house, the insulation in the attic floor separates the heated living space from the attic, and the roof sits above that cold space. Winter sun is also low and weak, and the roof is often snow-covered after storms, so there is little solar gain to lose. Heat escaping through gaps in the ceiling and into the attic is a much bigger factor in winter energy use. If you have a finished attic or cathedral ceilings where the insulation follows the roof slope, the roof assembly matters more. In that case, the type and thickness of insulation under the deck is the deciding factor, not the color of the metal.

Why do attic insulation and air sealing matter so much here?

Attic insulation and air sealing matter so much in New England because heating is the largest energy load in most homes here, and warm air rises. Heat that leaks into the attic is lost from the living space and can also cause problems on the roof. Many older Capes, Colonials, Victorians and triple-deckers have little insulation, uneven coverage or gaps around chimneys, attic hatches and knee walls. The U.S. Department of Energy publishes recommended attic insulation levels by climate zone, and much of New England falls in its colder zones. Air sealing is often as important as adding insulation, because air moving through gaps carries heat with it. A home energy assessment can identify where heat is escaping. Mass Save in Massachusetts and the energy offices in other New England states are good places to find current assessment and insulation programs.

How does ventilation fit in, and what about ice dams?

Ventilation keeps the attic close to outdoor temperature and removes moisture, which protects the roof deck and helps reduce conditions that lead to ice dams. A balanced system draws air in at the soffits and lets it out near the ridge. Ice dams form when heat escaping from the living space warms the roof deck, melting snow that then refreezes at the cold eaves. The ice holds back meltwater, which can work its way under roofing and into walls and ceilings. No roofing material prevents ice dams by itself; ice damming is excluded from the material warranty. The fixes are insulation, air sealing and ventilation, which address the heat loss at the source. During an Interlock consultation we look at the attic and venting with you, so that work can be planned along with the new roof.

What should I ask about energy when re-roofing?

When re-roofing, ask how the project will handle insulation, air sealing and ventilation, not just which roofing material is going on. Those are the parts that drive comfort and energy use. Useful questions include: how much insulation is in the attic now, and is it evenly spread? Are there obvious air leaks around chimneys, hatches, bathroom fans and recessed lights? Are bathroom and kitchen fans vented outdoors rather than into the attic? Is there enough intake at the soffits and exhaust near the ridge? For the roof itself, ask about the finish color and its reflectivity, and what warranty covers the finish. Interlock's Alunar® finish carries a 30 Year coating warranty. Be wary of anyone who promises a specific percentage of energy savings from a roof alone, since results depend heavily on the house.

Common questions