I came across a recent question that was answered by Michael Holcomb from the Byron Center in Michigan. His explanation is excellent in answering the question of “Is an asphalt shingle roof or concrete tile better, energy wise?”
Holcomb suggests that it’s a question that might have a different response depending on your location.He goes on to say, “Lets begin by reviewing how heat is transferred through roofing. Heat travels on light rays (radiant), in a vapor or liquid (convective) and through solid objects (conduction). When we say a roof is energy efficient we are speaking of its ability to reduce all three.In cold weather states conductive heat movement is not a function of roof coverings.All climate zones are concerned with radiant and convective heat transfer with regards to the roof structure.
In a predominantly cooling climate we should select a roof that reduces the impact of all three types of heat transfer since the sun radiates heat to the roof coverings which heat the roof structure conductively causing the attic to heat up. The heated air pressurizes the attic and may force the heated air into the habitable structure through convection.
So when we think of a roof covering as energy efficient we are almost always talking about how effective it is at reducing transfer of radiant heat into the attic via conduction or convection.”
When addressing the effectiveness of Asphalt shingles, he writes “Asphalt shingles are somewhat effective if you purchase a solar reflective roofing shingle. A percentage of radiant heat is bounced back into the atmosphere.
Unfortunately there is still enough heat that warms the roof and surrounding structure making the attic hot during sunny periods.
Since the asphalt shingles are in direct contact with felt underlayment and the felt is installed directly over the roof sheathing the entire structure is within a few degrees of the asphalt shingle temperature. Once the sheathing is heated up through conduction it warms up the attic which in turn warms up the living spaces through conduction and convection.”
He also contrasts them with Concrete shingles and says, “Concrete shingles are much more effective at reducing all three types of heat transfer.
Concrete tiles can be reflective in color which reduces heat gain.
Since they are elevated they actually allow the heat gain to be vented so the roof structure has significantly less heat gain.
The heated air under the shingles is vented through the ridge cap helping to keep the roof structure cool.
So strictly from an energy perspective concrete tiles are more energy efficient than asphalt shingles.”
See the rest of Holcombs explanation and thoughts in the next blog entry.