TPO, PVC and EPDM Need Appropriate Insulation

Falt roof insulationThe debate has been all but decided by government and communities alike to which color roofing membranes should dominate the tops of their buildings in their respective communities. Global warming zealots and community band wagon commuters will spiel on about urban heat island effect and the like to push white roofing membranes on all buildings. These certainly are important issues that we face and unquestionably need to be taken into consideration when choosing a membrane type and color.

Going green and environmentally friendly colored membranes have been covered in previous blogs but the color of the membrane must also be weighed against the actual location and design of your structure. If your building is above the Masson Dixon line then what is below the membrane can have more of an impact on how efficient any roofing system is in being green or perform otherwise. Insulation type, R ratings and the condition of the existing insulation or vapor barriers all have a cumulative effect. It is important to consider all the roofing components as well as the environmental variables, if and when you decide it is time for a new roofing system.

One environmental variable that cannot change is the location of your structure and the average temperature that will impact the roof on a daily basis. Northern cities will have substantially more days where the furnace is consuming those precious fossil fuels than their sidekick condenser is used in cooling the building.

According to Weather Data Depot’s calculator—and using a commonly adopted standard base temperature of 65°F, the results are listed below for 2014.

• Pittsburgh had 5,762 heating degree days to 811 cooling degree days.
• Cleveland had 6,286 heating days to 804 cooling
• Buffalo had 6,931 heating days to 516 cooling days.

To calculate the heating degree days, first find the day’s average temperature.
Add the day’s high temperature with the day’s low temperature and then divide by 2. H + L / 2 = avg. temp. Example: (high temp.= 60, low temp.= 40 this becomes 60 + 40 = 100 and is divided by 2.
This yields an average temperature of 50 degrees.)

To find the Heating degree days number, take the average temperature and subtract that number from 65.
Example (65 – 50 = 15 Heating degree days.)

For cooling days, follow the same process but subtract 65 degrees from the average temperature

The heating degree season begins July 1st and the cooling degree day season begins January 1st

It is obvious with these numbers that buildings in the Northern cities will spend more time and energy keeping their respective structures warm than cooling them. Insulation below the membrane thus can play a very productive role in keeping these structures efficiently warm or for that matter cool in the summer months.

Insulation set to workInsulation Flat Roof

Insulation below the membrane has one addition inherit property that surpasses any property that a color or type of membrane can bring to the table. Insulation works to keep a building efficient, 24 hours a day, regardless of the suns presence or absence. So whether its night or day, cloudy or sunny, the Insulation below the membrane is going to provide a continual benefit, in keeping the structure cool or warm.

Insulation and R values

The R-value is a measurement of thermal resistance of a solid material’s resistance to conductive heat transfer. The higher the R value, the higher the performance of the insulation. Pittsburgh, Cleveland and Buffalo are all in zone 5 and thus a commercial building would require a minimum of R- value of at least 20. Insulation entirely above the deck with a value of R-20 is the minimum for most building codes but the regulatory bodies of The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), International Code Council ( ICC) and International Green Construction Code (IGCC) recommend an R-value of R-30, R-25 and R-27.8 respectively.

Insulation r value chart

Additional layers of insulation to increase the building’s conservation of energy will minimize the impact of the choice of membrane color. Proper insulation below a white roofing system can be just as energy efficient as with a black colored roof in a Northern climate. If a white colored membrane is used in a Northern climate it is suggested that the insulation should be increased by an R-value of at least 3.5. The cost of this increased R-value is not usually substantial but the additional cost to compensate for condensation can be.

The real impact of a white membrane is in reflecting summer heat and in Northern climates; this energy saving potential can be offset by a black membranes value to absorb light in the colder winter months. Darker roofs can also help to melt built up snow and reduce the burden on the structure in the colder winter months.

There are additional variables to all roofing structures and how they act in application and conjunction to the roofing system. Roof mounted HVAC units will have to coexist and function with the roofing system they sit on. A darker membrane can affect the efficiency of a roof top mounted AC unit by raising the temperature of the ambient air in the hotter summer months. Lighter colored membranes have a higher potential for condensation in colder climates and this has to be addressed with an appropriate air barrier. With appropriate air and vapor barriers designed into your roofing structure, a lighter colored membrane installed over the correct insulation can be efficient in Northern climates.

As with all building structure decisions and their related systems, a building professional should be consulted before any decisions are made. The color of your roofing membrane is a choice that should be made only after a full evaluation of the building and its existing insulation or other structures are weighed against the one thing they are designed to foil, the local climate.

Jottan-Jorel offers a variety of commercial roofing solutions, including TPO, EPDM or PVC roofing membranes, for your new or existing structures. Jottan-Jorel specializes in preventive maintenance, emergency repair and service along with new and reroofing services.

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