A lot of energy can be lost through the eaves, making the home uncomfortable and increasing energy costs.
Eaves present an insulator with some challenges. A roof is lower at the eaves. If a sufficiently thick layer of insulation can’t be installed there, the eave R-value will be low, reducing the overall attic R-value. It’s also harder to blow insulation to eave areas; the low framing of an eave can interrupt the arc of blown insulation as it falls from the hose to the eave. In addition, if baffles aren’t installed correctly, the insulator may not be able to access the entire eave area to insulate it. Moreover, if the eaves aren’t closed off from the outdoors, wind can blow insulation away from eave areas, leaving them completely uninsulated.
When an HVAC system is heating the home, poorly insulated eaves act as "cold spots," where heat from the living space can transfer up through the attic and out of the home by convection. When an HVAC system is cooling the home, poorly insulated eaves act as "hot spots," where heat from the sun can transfer down into the living space through the attic by radiation. In addition to making the home uncomfortable, energy loss through the eaves increases the homeowner’s energy bills. As heat transfers through the attic, the HVAC system has to produce more heating or cooling to maintain the homeowner’s desired temperature.
Cause 1:
Low eaves
Often, eave framing isn’t high enough for insulation to be installed at the eaves. Many popular truss types aren't designed to provide a sufficient eave height for insulation. For instance, a sloped ceiling created with scissor trusses typically isn’t high enough, because scissor trusses don’t have deep enough heels to fit a sufficient layer of insulation.
Solution
Build a higher eave with an energy or raised-heel truss; this is a purchasing decision. Energy and raised-heel trusses allow insulation to be installed to the required thickness. Another solution is to install compact batts at the eaves. Compact batts can provide an equivalent R-value at a lower height. Or, opt for spray foam insulation, which expands to fill the entire truss web at the eaves to provide sufficient R-value.
ProTip!Compact batts and spray foam insulation are expensive, and their installation can increase the construction cycle time. A better solution is to specify a truss that makes the eave high enough to be properly insulated.
Cause 2:
Lack of end dams
If end dams aren’t installed at the eaves, wind can blow into the attic and “wash” insulation away from eave areas, leaving them completely uninsulated. Baffles, which are installed to ensure a ventilation path, often double as end dams; however, an insulator typically won’t put a baffle in every attic bay. In attic bays with no baffle, the framer may fail to close off the eave to the outdoors with an end dam. This mistake allows wind to wash away batts, blown fiberglass, and blown cellulose.
Solution
Cover the eave area with end dams. One method is to extend the wall sheathing up the eave. This method works well if the roof trusses have vertical legs. Another method is to bend the baffles down to cover the eaves. Baffles typically come perforated so the insulator can bend them down. If baffles are used as end dams, be sure that attic bays with no baffle have some other type of end dam installed. If the roof trusses are high wedge or inset trusses, the end dams will need to be higher to protect the eave.
Cause 3:
Poor blowing methods
If an attic is large, such as if it has 40’ trusses, the insulator can't possibly reach the eaves by standing in the center of the attic and blowing toward them, but this is often what insulators do. In a large attic, it's common for the insulator to blow an insulation layer of insufficient depth at the eaves.
Solution
Make sure the insulator walks to the eaves to blow the insulation. Another solution is to install compact batts at the eaves. Compact batts can provide an equivalent R-value at a lower thickness. Or, opt for spray foam insulation, which expands to fill the entire truss web at the eaves to provide sufficient R-value.
Cause 4:
Poor baffle installation
Before the attic is insulated, a crew installs baffles, end dams, and depth gauges. This crew usually has very little guidance. If the crew positions baffles on the insides of the exterior walls, the insulator won't be able to insulate the top plates. Another common mistake is to install the baffles too low, allowing blown insulation to fall into the ventilation gap between the baffle and the roof sheathing; this prevents proper airflow through the baffle for ventilation.
Solution
Attach baffles to the exterior faces of the top plates, so the insulation can fully cover the top plates. Also, maintain a 1" ventilation gap between the baffle and the roof sheathing. To keep blown insulation from falling into the ventilation gap, install the baffles so that they extend up the roof interior at least 6" beyond the insulation level.
