Does Shiny Reflective Foil Insulation Work?February 16th 2012
Recently I have addressed insulation with a few callers to my office, and in most cases, I mentioned batt insulation, fibreglass or rock wool, as well as rigid foam, poly urethane or expanding polystyrene insulations. These products are commonly used by builders as well as the do-it-yourselfer, but not always in the right way.
Batt Insulation (fibreglass or rock wool) - applications include horizontal and vertical or walls and ceilings.
Loose Fill Insulation (fibreglass, rock wool, cellulose blown-in insulation) - Normally used for ceilings and roof cavities but some applications are available through specialty contractors.
Blown-in Polyurethane Insulation (Icynene) - Professionally installed into vaulted roof lines, basement walls, crawlspaces, and cantilevered floor systems.
Now for the real reason for this article on insulation: What about reflective foil insulation? What are the advantages of reflective insulations? What is conduction, convection and radiation? These are three ways that heat moves from warm to cool regions.
Conduction: Heat flows through material i.e. from a stove element to your cooking pots and pans
Convection: Heat flow transferred by movement of air i.e. your modern convection oven
Radiation: electromagnetic transfer of energy through space i.e. your microwave oven
Lets look at common applications for reflective foil insulation, keeping in mind we want to cut down the conductive heat that may occur in locations we don't address with common insulation applications.
1) Roof structure - under the roof deck plywood you will have conductive heat being transferred from the roof shingles to the plywood / roof decking material into the attic cavity causing heat gain in the attic cavity. This is transferred by conduction from the hot insulation batts to your drywall ceiling. Now the ceiling is radiating heat to the living area of your home.
By applying reflective foil insulation to the underside of the roof plywood, you are going to reflect 95% of the radiant heat that is encountered by the heat conduction transfer from the shingles and the plywood, producing a cooler roof cavity, giving you a more comfortable living area below. This may produce up to a 10% savings on your air conditioning costs.
2) Floor applications - floors suspended over crawlspaces can be very cold in the winter months, batt insulation will help give you comfort but not as well as a reflective surface or foil insulation suspended under the floor joist system. Warm air seeking out those cold areas below, will be interrupted by a shiny surface of foil reflecting the energy back to where you want it, on the floor surface, adding comfort and dollar savings.
Other applications for foil insulation would be cantilevers retro insulation for walls, ceilings, garage, workshops, sunrooms, and anywhere radiant heat is being generated by conduction or convection. Products commonly found in your local building centers under the EnergyStar ™ brand, such at Reflective Foil, IE Reflectix are easy for the do-it-yourselfer to install.