An unconditioned attic is an extremely important area of the home to insulate. The U.S. Department of Energy (DOE) estimates that up to 45% of a home's energy loss can occur through the attic if the insulation is missing or isn't installed correctly.
Energy efficiency has seen increased attention in the media recently. Major programs like ENERGY STAR and big companies like Owens Corning® are helping to broadcast the message to the public that properly installed attic insulation is essential in helping to reduce energy bills. With more homeowners and prospective homebuyers taking a peek in the attic, it’s important to make sure insulation is installed at the correct depth, density, and coverage, as well as to ensure that the R-value that’s advertised is reflected by what’s installed.
Energy loss through the attic
The three key areas of an attic where energy loss typically occurs are through the attic bays, eaves, and mechanical obstructions. When these areas are poorly insulated, heat transfers through the attic, forcing the HVAC system to produce more heating or cooling to maintain the homeowner’s desired temperature.
During the heating season, areas that are poorly insulated act as “cold spots,” where heat from the living space can transfer up through the attic and out of the home by convection. During the cooling season, these areas act as “hot spots,” where heat from the sun can transfer down into the living space through the attic by radiation.
Insulation works best when air isn’t moving through or around it. So, your strategy in the attic must include sealing air leaks before installing the insulation. Air sealing helps ensure that you’re getting the best performance from the insulation.
The maximum thermal performance (R-value) of insulation also heavily relies on proper installation. Insulation with gaps, insufficient depth, and inadequate density will deliver a lower R-value than what the manufacturer has stamped on the batts or written on the bags. While the nominal R-value of the attic insulation may be 38, if it’s installed poorly, its actual R-value may be below 30.
Next, we're going to look at the two types of insulation commonly installed in attics: batt insulation and blown (loose-fill) insulation.
Properly installing batt insulation
Attic batts are deeper than wall batts; they’re also slightly wider, so they expand over the attic framing just enough to touch each other, providing better coverage. Common installation mistakes, such as gaps and compressed areas, often prevent batts from providing maximum heat resistance in the attic. However, if attic batts are prepared and installed correctly, they can achieve the required R-value and provide almost continuous coverage in the attic.
Before installation, make sure the batts are full-dimension attic batts, and confirm that the batt type and quantity will yield the required R-value. Bounce individual batts on their side to fully recover their original thickness. Measure them to make sure; for example, a fully recovered R-38 attic batt should be 12" thick.
Install an attic batt by pushing it up about 1" past the bottom truss chords or ceiling joists on either side. Then, pull the batt down so its edges are flush with the framing; this creates friction on both sides of the batt to help it expand. Attic batts should hang slightly between the trusses or ceiling joists, creating a 1" belly, so they’ll be in total contact with the drywall when it's installed. If the batts are faced, make sure the facing isn’t wrinkled; wrinkles will cause the batts to sit too high in the attic bays. If you’re using batts that are 4’ in length, make sure they’re touching snugly end-to-end. Also, confirm that the batts’ facing overlaps 1/2". For more Best Practices®, visit BuildIQ Toolbelt: Attic Insulation.
Properly installing blown insulation
Blown insulation—or loose-fill—is insulation that’s blown into place through a hose. The installation takes at least two people—one person to monitor the hopper and another to blow the insulation into place. In the hopper, keep the insulation at a certain level, so the hose can supply the correct density. If the picker inside the hopper is visible, the insulation level is too low. It’s important to follow the blower instructions, as well as the blowing chart for the insulation, during installation.
Install blown insulation by blowing it parallel to the trusses or ceiling joists. Make sure to walk all the way into remote areas of the attic, as well as around and behind framing obstructions. Once a section of the attic is blown, make sure the insulation is the correct depth at depth gauges and the density is consistent. After installation, the attic baffles should be visible above the insulation. Confirm that insulation hasn’t been blown into the 1” ventilation gap between the baffles and the roof sheathing and that the top plates of the exterior walls are covered with insulation. For additional Best Practices®, visit BuildIQ Toolbelt: Attic Insulation.
Remember that the mere presence of insulation isn’t enough to achieve the required R-value in the attic. Batt and blown insulation have to be installed correctly in order to realize their full R-value.
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