Question

Do cool roof asphalt shingles make sense in our cold climate area?

Asked by Lia Monahon
Everett, MA

Re-roofing sloped-roof, poorly insulated house in Boston area. We'd like to find cost-effective green build options for our new roof. We're considering the rubber roof materials but are wary of the cost. Cool roof asphalt shingles (like GAF Timberline Cool Series) seem the most cost-effective way to reduce the reflective heat problem (though I guess they don't address the green materials problem). I've read that cool roofs may actually increase the heating costs in the winter months in cold climates. Our two-family home was built without exterior insulation. We recently blew in insulation, but I'm not sure it made much of a difference and our heating bills are still astronomical. So I'm wary of a roof that makes the house work harder to stay warm during the winter. Thanks!

Answer

Lia,

In your case and climate it makes no economic sense to install a cool roof shingle.

  • Your choices for green options are limited to recycled-content asphalt shingles and metal roofing.
  • The cost of metal roofing may prove shocking.

Cool roof shingles

Cool roof asphalt shingles work by reflecting radiant heat back towards space rather than absorbing that heat into the roof structure. In the summer months this may reduce your cooling costs.

In cold weather months the reduced attic temperature from lost radiant heat will encourage additional convective heat loss from the house adding to your heating costs.

Air seal first

Since you added attic insulation without seeing much cost improvement in heating your home I would suggest that the insulation contractor did not seal the air leaks between the conditioned spaces of the home and the attic.

  • The convective heat loss through those leaks is the greatest method of heat transfer in a cold weather state.
  • Air sealing an attic before adding fibrous insulation can reduce energy costs by 50% or more.

Stopping convection (air leaks) makes the fibrous insulation more effective at stopping conductive heat loss. Any heat or moisture buildup in a properly sealed and insulated attic is then vented to the outdoors through the roof vent system.

If your attic were well sealed and insulated, cool roof shingles would reduce your cooling costs without increasing your heating costs.

  • I recommend contacting a home weatherization contractor to see if it is possible to air seal the penetrations through the floor of the attic to improve the thermal performance of your home.
  • If the attic can be sealed adding cool shingles would be a positive investment. If air sealing is too costly at this stage cool shingles would not be a benefit.

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