attic radiant barrier insulation bay area

Radiant barrier 'chips': unlike sheet-type radiant barriers, these 'chips' are blown onto the floor of the attic - typically to a depth of 3 or more inches. The efficacy of the decking’s ability to pass moisture is more important in humid climates. The perforations are intended to allow the decking to “breath” allowing the passage of moisture. Some products laminate a non-perforated radiant barrier, some products laminate perforated radiant barrier, and some products perforate the product after the foil is laminated to the decking, penetrating the foil, glue, and substrate. The main difference among these products is if and how the laminated foil surface is perforated. The first layer of foil will reduce radiant heat gain by at least 90%, making the reduction provided by the second layer of foil insignificant.įoil-faced roof sheathing materials (decking): these products come from the manufacturer with a foil facing adhered to one side of the sheathing. In an attic ceiling or roof deck application (locations 1 and 2 in Figure 1) there is no significant performance difference found between single-sided foil and double-sided foil. The strength of the backing material is important since unreinforced foil tears very easily. Some products are further strengthened by fiber webbing sandwiched between the foil and the backing. These products are available as single-sided or double-sided foils with another material as backing, such as craft paper, mylar, or polypropylene. These benefits can be particularly valuable during heat waves, or extreme heat events.įour generic types of radiant barrier are most common:įoil sheet products: these products are available perforated (vapor permeable) and unperforated (vapor retarder). They improve comfort inside the home, reduce wear on air-conditioning equipment, and extend the conditions in which an air-conditioning system can meet the cooling load. Radiant barriers provide more than just energy savings in warm climates. A simple savings calculator tool is available here: Oak Ridge National Laboratory's Radiant Barrier Calculator. In climates where summer heat gain from the attic is minimal, the advantages of a radiant barrier diminish. However, if the HVAC duct work is in the attic, a radiant barrier keeps it cooler during the summer, which can be a significant benefit. Attic insulation levels have a large impact on the amount of heat flow that is reduced by 40% in other words, if you have little or no insulation in your attic, a 40% reduction is very significant, but if your attic is insulated to R-30 or better, there is very little heat flow to reduce.

This means that the portion of the cooling load represented by the attic is reduced by 40%, which typically equates to 8% to 12% of the annual cooling costs.įurther clouding the savings question is the impact of attic insulation levels and geographic location. This does not mean a radiant barrier will reduce the homes’ energy use by 40%, as many advertisers claim. A radiant barrier system can reduce the heat flow into the house from the attic by approximately 40%. Two things affect the performance of a radiant barrier system: the level of insulation in the attic and the geographic location of the home. Third, its vapor permeability is very low. Second, it emits (gives off) very little heat. First, it reflects thermal (long-wave infrared) radiation very well. Figure 1. There are three potential locations for an attic radiant barrier – adhered to the underside of the roof decking, hanging from the rafters, or on the ceiling insulation (Source: Radiant Barriers: A Question and Answer Primer 2005).Īluminum foil, the operative material in attic radiant barriers, has three physical properties of interest. Other types of radiant barriers such as “chips”, foil faced air bubble-packing, and multi-layer products, are acceptable for location 3 (more below). Only locations 1 and 2 are recommended for sheet radiant barriers because dust will accumulate on the radiant barrier if it is installed at location 3. Figure 1 illustrates the locations in which a radiant barrier may be installed in an attic.

A radiant barrier is typically a layer of reflective aluminum foil material placed in the attic next to an air space to block radiant heat transfer between a heat-radiating surface (such as the underside of the roof deck) and a heat-absorbing surface (such as insulation at the attic floor).

Attic radiant barrier insulation bay area