Green Roofs - Slow Absorption & Release Heat Sinks

 

We've compiled data over the last year on how an Extensive Vegetated Roof absorbed and released solar energy (heat) over a twenty four hour cycle.

The roof under study is not insulated.  It has a tongue and groove pine deck with asphalt roll paper and asphalt shingles.  The interior was non-temperature (no heat or HVAC) controlled during the study periods.

The temperature measuring points were the exposed roof tongue and groove decking surfaces and consisted of multiple point averages.  Readings were taken with an EXTECH IR AN200 Unit.

The following illustrations depict a trend we've seen over and over:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The extensive vegetated roof systems absorb solar heat slower than asphalt roofing.  The extensive vegetated roof systems also retain the heat longer and then release the absorbed solar heat slower than asphalt roofing.

The linear trendlines for the temperature curves tell an important story also.  The ambient air temperature and the decking under the non-insulated asphalt shingle roof temperature possess more significant vertical trendline movements.

The temperature swings of the decking under the green roof are much more linear - showing a narrower range in temperature swings.

The data shown here is representative of spring, summer, autumn and winter with summer and winter having the more pronounced curves.
 

Importantly, we believe extensive green roofs, such as the one we are studying in this case, moderate temperature swings.

The data also points to the fact that green roofs serve as a heat sink, slowly absorbing solar heat during the daylight hours then slowly releasing the heat during the evening dark periods.

During the winter, green roofs may help by moderating cold temperatures at night by releasing heat back into the structure.  However if insulation separated the green roof from the structure then little or no heat would be recaptured unless a heat capture coil or other mechanism existed.