Radiant Barrier Insulation and Stopping Attic Heat Gain
This entry was posted on December 15, 2009.
What actually happens in your attic and how are radiant barriers effective?
To answer this question we need to look at how your attic works in the form of heat transfer.
As the heat from the sun warms your roof deck, this heat is passed through the roof into the roofing materials and into your attic. This is conductive heat transfer. From here, this heat is radiated through the attic warming everything it contacts. This is radiant heat transfer. As the radiant heat contacts the fiberglass insulation, it converts to conductive heat transfer again and warms the fiberglass insulation and your ceiling below and into your cooler living space.
The warmer the attic space, the more heat is transferred into your living space. If your attic temperature is 140 degrees which is common in summer months, this 140 degree heat is constantly robbing your cooler inside air.
You cannot stop attic heat gain but there are three options that you can do to lessen this heat transfer, thereby saving you money.
- Increase attic ventilation: If you do not have enough attic ventilation there is nowhere for the climbing heat to flow and your attic will heat up much quicker than if you had appropriate ventilation. Add louvers, passive attic fans, or soffits and ridge vents to correct this problem.
- Increase the amount of fiberglass insulation: Few homes are built today and none were built yesterday with the correct amount of fiberglass insulation. Contact your local building department for recommended thicknesses. If adding fiberglass in batt form, make sure to run the batts perpendicular to the original insulation. As the radiant heat that permeated the attic contacts the insulation, there is more resistance or R-value to slow the now conductive heat buildup.
- Add a radiant barrier: Radiant barriers naturally reflect 96% of radiant heat. The addition of foil insulation will lower your attic temperature. Radiant heat that before passed through the roof deck and onto the fiberglass insulation is reflected back out of the roof deck and away from the home. Using the same example from above, now your attic temperature with a radiant barrier is 110 degrees. Now only 110 degree heat is constantly robbing your cooler inside air. This 30 degree temperature difference results in much less attic heat transfer and saves you energy.
This is exactly how radiant barriers work in the form of attic insulation in warm months and are effective at lowering your utility costs. Used in conjunction with correct ventilation and correct fiberglass insulation levels, you can be sure you have the most energy efficient attic possible.