Radiant Barrier FAQ's
WHAT IS HeatBloc-75? WHAT IS HeatBloc-75?HeatBloc-75 is an aluminum colored, water-based, low emissivity (low-e) coating. When applied to building materials such as plywood, OSB or plasterboard, HeatBloc-75 lowers their surface emissivity to 0.25 or lower, thereby blocking 75% of the radiant heat trying to enter the home. It is classified by ASTM as an Interior Radiation Control Coating (IRCC) and may be effectively used as an interior radiant barrier. HOW DOES HeatBloc-75 WORK?HeatBloc-75 radiant barrier works by changing the emissivity of the surface where it is applied. Building products such as wood, brick, and plasterboard have high emissivities (0.7-0.95). When heated, they radiate most of their heat to cooler surfaces by allowing the heat to penetrate the roof into the attic and from the attic into the house. HeatBloc-75 lowers their surface emissivity to 0.25, lessening their ability to radiate heat and therefore letting less heat penetrate the roof into the attic. WHAT IS A RADIANT BARRIER?Heat penetrates buildings in three ways: conduction, convection and radiation. Radiation is the transfer of heat by electromagnetic waves known as thermal radiation. Thermal radiation is a form of invisible light that travels through the air from a warm to a cool surface. Warm surfaces, such as roof decks warmed by the sun, will radiate or emit their heat to cooler interior building surfaces. Radiant barriers address heat flows by radiation. A radiant barrier is a low-e surface placed in the path of thermal radiation that blocks heat transfer. WHAT IS EMISSIVITY?Emissivity is the ability of a surface to radiate or emit energy in the form of long wave electromagnetic radiation. It is represented by a value from 0 to 1. The closer the value is to 1, the less effective the surface is at impeding radiant heat transfer. Wood has an emissivity of 0.90. Thus, when wood is heated above the temperature of surrounding surfaces, it will tend to transfer 90% of its heat energy by radiation. HeatBloc-75, when applied to most non-porous surfaces, will decrease the surface emissivity to 0.25 or lower, allowing only 25% of the heat energy to be transferred by radiation. WHAT IS THE ROLL OF AIRSPACE WHEN USING HeatBloc-75?To function effectively, a radiant barrier must face an airspace of 1" or greater. A radiant barrier will not function if sandwiched between two solid surfaces. HeatBloc-75, when installed on the underside of roof decking, normally faces downward into the attic. If insulation is installed in the cavity formed by the roof trusses and roof decking (as in a cathedral ceiling), at least 1" should be allowed between the top of the insulation and the HeatBloc-75 surface. DOES HeatBloc-75 DEGRADE OVER TIME?HeatBloc-75 does not lose its effectiveness over time like some radiant barriers. Foils can tear and require the staples to penetrate the barrier. Foil chips can accumulate dust, which diminishes their effectiveness. WHAT IS THE COVERAGE RATE FOR HeatBloc-75?Recommended coverage for HeatBloc-75 is 325 - 425 square feet per gallon depending on the porosity of the substrate. WHAT IS THE RECOMMENDED APPLICATION METHOD FOR HeatBloc-75?For best results, spray application using a spray pump size ¾ GPM or greater, 2,000 psi and tip size of 0.019” to 0.021”. The product can be rolled with a 3/8” synthetic nap roller, however, roofing nails penetrating the surface can make brushing or rolling difficult. IS HeatBloc-75 PERMEABLE TO WATER?Yes! HeatBloc-75 allows water vapor to permeate, and does not trap water vapor within roof decks or sidewalls. This is vitally important in attic conditions. CAN HeatBloc-75 BE USED ON SIDEWALLS?Yes, but HeatBloc-75 is normally more effective when used under roofs. Roof surfaces are generally much hotter than sidewalls. Up to 80% of the summer heat gain is from above. Low e surfaces become more effective in controlling radiant heat transfer as the temperature of the radiant heat source increases. However, in tropical climates where no insulation is used in sidewalls, HeatBloc-75 can substantially help increase interior comfort levels. CAN HeatBloc-75 BE USED IN VENT-SKIN CONSTRUCTION?Yes. In vent-skin roofs HeatBloc-75 should be applied on the underside of the outer roof skin facing down into the vent channel. On vent-skin sidewalls HeatBloc-75 should be applied on the inside of the outer skin facing into the vent channel. CAN HeatBloc-75 BE USED WITH RADIANT HEATING SYSTEMS?Yes. It is an effective heat reflector when used behind wood stoves or on walls adjacent to ceiling mounted radiant heaters in commercial applications. IS ATTIC VENTILATION IMPORTANT?Absolutely! Radiant barriers only control radiant heat loads. Good attic ventilation helps control convection loads. Together they raise the comfort levels and lower cooling costs. Venting to allow 2.5 air changes per hour should be specified as a minimum. DO RADIANT BARRIERS LOWER HEATING COSTS?Yes, but only modestly. They are most effective at lowering cooling costs. DO RADIANT BARRIERS HAVE AN "R" VALUE?No. R-values apply only to solid insulation or to insulating systems that control heat flows other than radiation. In independent testing of the product at the University of Kansas, the R-value of the insulation, after applying HeatBloc-75 to the roof deck, increased by 87% to 98%. |