Question

Is an Energy Star roof worth the cost in a climate where there are more heating degree days than cooling degree days?

Asked by Anne Lewis
Pierre, SD

We are looking at re-roofing our home. The salesman indicated that in our climate an Energy Star rated roof was less important than good attic ventilation for keeping the house cool. We can have high summer temps (100°+) for a few weeks each summer, low winter temps (-20°), for about the same amount of time, high winds and hail. What do you recommend for roofing other than metal?

Answer

Anne,

It would be difficult to make a statement concerning value without knowing the cost difference in materials. 

  • Pierre, South Dakota is predominately a heating region with 7,580 heating degree days and 450 cooling degree days.
  • Investments to reduce cooling costs will have a lower return on investment than improvements to heating efficiency.

I will give you my experience in making roof replacement decisions on my own home later in this response.

Seal ceiling penetrations

Sunlight warms the roof which in turn heats up the air in the attic.

  • As the air warms in the attic it expands (creating pressure).
  • As the pressure builds the warm moist air can find its way into the living space by convection and conduction.
  • This is the same way that heat is transferred to the attic from the living space during cold weather months.

Fibrous insulation is ineffective at stopping convective heat transfer.

Every penetration in the ceiling (wires, pipes, light fixtures, partition walls, etc.) all allow for air to move freely between attic and interior of the house.

The illustration below shows the effects of convection in fibrous insulation during the heating season.

My own experience

On my home I stopped all the air leak pathways between the house and attic.

  • This step reduced my heating costs by 50% the first year.
  • Then I added a single solar roof vent to remove excess heat/moisture during the peak summer daylight hours.

At night the attic vents well through two small gable end vents.

Metal roof vs asphalt shingle

I was contemplating a metal roof thinking that I might install a thin film photovoltaic system in a few years.

  • The cost of a 50 year, metal roof was 3 to 5-times higher than a 30-year asphalt shingle roof.
  • I opted for a light-colored, $7,000 asphalt shingle roof rather than a $21,000 - $35,000 metal roof.

At 62 I would be called an optimist if I thought I would be in this house long enough to install a replacement roof so the 30-year asphalt shingle roof served me well. I did go with a lighter color shingle so I do enjoy some reflective quality, reducing summer temperatures in my attached garage by about 5-degrees.

Seal down shingles are almost standard and stand up well to high winds. An asphalt shingle roof tolerates hail better than metal roof (not to mention foot traffic). If I decide to add a PV system I can mount it on a pole in the field to the west of the house rather than on the roof.

Your decision

Make your decision based on your budget and your planned tenure in the home.

Metal roofing costs vary wildly. I actually located a local manufacturer that specialized in commercial roof and his costs were 40% lower than the franchise metal roofing contractor. Even so it was 300% higher than an asphalt shingle roof. If I were younger I might have opted for the metal roof.

You’ll have to look at your variables and make a decision that works for you. 

I wouldn’t recommend a solar reflective roof in your climate zone unless the added cost is minimal (3 – 5%).

Radiant barriers

One of the latest insulation contractor fads (in Michigan) the past two years is the installation of radiant barriers on top of the attic insulation.

I have inspected more than 200 of these installations because clients were experiencing increase heating costs rather than the 20% reduction the radiant barrier manufacturer advertised.

The problem was moisture buildup under the moisture barrier which moistened the insulation making it less effective.

Choosing a roofing contractor

Make sure you check references. Go visit two or more of the contractor’s previous clients to see how the work looks and to ask how they liked working with the contractor.

  • Verify licensing (if required in your area), workman’s compensation and general liability.
  • Ask for current certificates of insurance from their insurance company.

It is a little extra work but well worth the peace of mind. In some states if a contractor does not have workman’s compensation and they are injured on your property you could be liable. Don’t let that happen to you.

 

Good luck,

The General

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