Radiant Barriers – How Do They Work?

Radiant barriers are basically insulation devices used to maintain temperature of the surroundings. They are mainly composed of reflective aluminum sheets placed on substrate material. The substrates are made up of brown paper, craft paper, plastic films, cardboard, plywood sheathing or air infiltration barrier material.

There are two major types of radiant barriers i.e. Spray on and Sheet Barriers. Installation of spray on barriers is very simple. It is just sprayed on the underside of roof. It is made up of paint and metal flecking mixture. This mixture has enough reflective property to reflect the heat. Spray on barrier is durable. The sheet radiant barrier comes in the form of large roles. It can be installed by rolling out on the whole attic. You can roll it up on entire top insulation, hang it from rafter supports, nail it to bottom of the roof or roll it out underneath shingles.

All types of radiant barriers have same basic working principle. Heat exchange occurs due to thermal radiation. Radiant barriers minimize this heat exchange between roof deck and the attic floor. They have a high ‘reflectivity value’ (usually 0.9 or 90%) and low ‘emissivity value’ (usually 0.1 or less).

The reflectivity value determines the amount of radiations reflected by the surface. It has a value from 0 to1 or 0% to 100%. The emissivity value determines the amount of radiations produced by the material. It has a value from 0 to 1. A surface with high emissivity value will produce more heat radiations.

During summer, roof absorbs lots of solar energy. Radiations are produced by roof sheathing underside and roof framing areas. Due to conduction process, heat travels from top of the roof to lower cooler areas and air pipes. Radiant barrier reflects these radiations back to the roof. This keeps the insulation layer cooler. And less heat moves through insulation into the room. Roof mounted radiant barriers reduce the amount of radiation that strikes the insulation. This lowers the temperature of insulation layer. As a result, less heat flows through the insulation.

During winters, solar energy is lost from the attic. Radiant barriers reduce this heat loss. They minimize the amount of energy radiated from the top surface of the insulation. However, solar heating of the roof may also result in loss of some beneficial heat gains. More research is currently underway to determine the affectivity of radiant barriers in winter season.