Breathing a sigh of relief  

by Bob Bruttell, President 

What spells RELIEF may surprise you.

If you are a cat on a hot tin roof then I pity the fool... With apologies to Tennessee Williams and Mr. T - you just don't want to go there. On a hot tin roof, I mean.

Roofs can get very, very hot. Some days you probably could fry an egg on a hot tin roof. That would be messy so you probably don't want to do that either.

However it is important to know that the typical black roof can get to 170 degrees when the ambient temperature is in the 90s. That might not be hot enough to fry an egg but it is too hot to touch.

Super heated roofs can have some very detrimental implications. First, a sizzling hot roof can make the people inside swelter. A hot roof isn't even very good shade because the heat transfers, warms the air below and makes it exceedingly uncomfortable for those trying to work below. (Adequate insulation in place can resist the conductance of heat - but that is a whole other story - see below.)

In the last few years, the roofing industry has begun to take a good look at the problem of hot roofs. Roofs are now rated for reflectivity, that is, they are rated for how much of the sun's heat is sucked in or reflected away. As you might expect the typical black roof has little or no reflectivity. The sun's rays are in fact captured by the roof assembly. The roof becomes a "heat sink" transferring all that heat to the cooler air below - not a good thing.

All those roofs becoming "heat sinks" also causes the "heat island effect." Chicago and Los Angeles now mandate reflective cool roofs so the roofs on their buildings do not super heat urban temperatures.

One solution for black asphalt "heat sinks" is to coat them with a so-called "silver" coat: a solvent based coating that has aluminum flakes in it. This will do some good. A better idea might be a white emulsion or urethane coating. More expensive, but more reflective and effective. 

EPDM rubber manufacturers now recommend a white acrylic coating that can be applied over a fully-adhered rubber roof. We know of one case where the technicians working in the non-air conditioned sections of a shop breathed a sigh of relief when we coated their black roof with white acrylic. At least now the roof provided good shade.

One manufacturer of white PVC roof products has registered the trade name "Cool Roofs" to brand their products. A white PVC roof can provide exceptional reflectivity of as much as 93%. A roof that has that much of the sun's heat reflected away will only be heated to about the ambient temperature.

Cooler roofs save a lot of  money. When you have a roof that is not holding in the sun's heat you are no longer having to cool super-heated air.  In that case your air handling equipment breathes a sigh of relief. It does not have to work overtime to cool the building. Your electric meter is not spinning wildly.  And the occupants of the building are much more comfortable.

Add to a cool roof some good insulation with a high R-value and you will begin to save real money in both summer and winter. Take a serious look at highly reflective roofs. This may even make the bean counters breathe a sigh of relief - if that is possible.