Ventilation And Your Roof
Reducing “heat gain” on roofs equals lower cooling cost. Adequate ventilation reduces cooling requirements and energy consumption, and extends the life of your roof and structural members.
Cooling load/Heating load for Roofing
Your home and/or business is a container that should keep you safe from the outdoor elements of rain, snow and excessive amounts of heat and cold during the appropriate months. The indoor environment is greatly effected by temperature, humidity and breathable indoor air quality (known as IAQ). Your roofing system is simultaneously the most exposed portion of your home/business to the outdoors and plays a part in containing and managing much of your indoor environment So, the question arises: How can we create the best balance between elemental protection and indoor environmental control through your roof system?
Here is where we address Cooling Load and Heating load.
Your roof acts as a transfer medium for heat into your home/business at all times of the year. This can be a good thing during the Winter months and a bad thing during the Summer months. And, here we are talking about physical comfort and the amount of energy it takes to cool or heat the living/work space to achieve that comfort.
Latitude and direct exposure to the Sun plays a large part in this equation. Denver, Colorado, USA is our local benchmark..
The amount of energy that is transferred as heat into your home/business is determined, to a large extent, by the Solar Reflectance index (SRI) values of the roof system. This is a measurement of the solar reflectance and solar gain through the visible and non-visible wavelengths of the Sun’s light and energy on the roof surface (ref LEED-NC, version 2.2). The reflectivity of roofing varies greatly, depending mostly on the color of the surface and other factors such as the type of paint/coating, granule or chemical component of the surface. Emissivity, which is related to solar gain in how quickly the surface releases heat, is greatly determined by the substrate beneath or within the roof surface and the chemical composition involved. White and light pastel colors and coatings, galvalume steel substrates, some tile, poly-vinyl-chloride (PVC) and tri-polymer-olefin (TPO) all tend to have high solar reflectance ratings (SRI). These concepts of thereflective and emissive properties of roofing material are well worth considering when installing steep and low slope roofing systems to keep out the weather and reduce the energy consumption that comes withextreme Cooling Load demand.
Though there are benefits to passive solar gain through a roof system in the colder months of the year, especially in more Northern latitudes, there are better ways to use the Sun’s warming energy that will not advance the damage and depreciation of the roofing structural medium.
Consider thermal solar systems for hot water, radiant floor and holding tank home heat. Also note passive solar gain through low E glass windows and skylights and concrete and stonewalls and tile and stone flooring. For a cost comparison between heating load and cooling load ask us about the Cool Roof Calculator.
Air is the medium that holds heat in you home or business. If hot air can be moved out of your building quickly, the temperature will drop, the amount of energy it takes to cool the air will drop, the subsequent cooling cost will drop with lower consumption of non-renewable fuels, and, your physical comfort will increase!
Ventilation is the active partner of roof reflectivity and emissivity (ref SRI index, LEED-NC Version 2.2) and in some cases may be more important as a cooling factor for your home/business.
To maximize the movement of hot air through an attic/void there should be a balance, ideally, of 50% intake venting and 50 % exhaust venting.
The typical intake vent is a rectangular metal louver with screen that is placed at the underside of a soffit (the overhang on residential and some commercial buildings). The typical exhaust vent is a square metal capped vent that can be seen near the ridge of a sloped roof.
There are several other systems for ventilation such as gable vents for intake and exhaust, electric and solar powered roof fans, whole house fans and the like. One of the most balanced and efficient passive systems (not requiring electricity or moving parts such as a fan) is comprised of continuous soffit vent and continuous ridgevent.
Minimum code requirements call for one square foot of vented net free area (again, ideally balanced between intake and exhaust) for every 300 feet of attic floor space. To really achieve adequate ventilation it is recommended that the net free area for venting be twice as much as that recommended by code.
Please contact us with questions about sizing your ventilation system.
In the cooler months of the year, heat and moisture from inside your home/business will have a greater tendency to migrate through walls, ceilings and roofs to the outdoors. If there is no adequate pathway for the movement of this heat and moisture, it tends to get trapped in walls, ceilings and attic spaces. Under these conditions, mold and rot can quickly damage structural members and insulation. Here again, balanced ventilation and good insulation play a very important part in keeping the attic space temperature neutral and dry.
Ask us about the negative effects of snow as insulation and the benefit of ice and water guard at eaves, valleys and other details.
Contact us for a ventilation analysis of your home or business today.
You may use our convenient request an inspection form to have us take a look at your roof. You will receive a response within 24 hours.
Or contact us at firstname.lastname@example.org