A lot of energy can be lost through mechanical obstructions, making the home uncomfortable and increasing energy costs.
Mechanical features in the attic, such as wires, ductwork, and mechanical platforms, can make it difficult for the insulator to install enough insulation. Wires and ductwork can interrupt the arc of blown insulation as it falls from the hose to the attic bays. If the HVAC system is in the attic, it has to be supported by a mechanical platform. The mechanical platform often isn’t high enough for a sufficient depth of insulation to be installed underneath it. The platform can also get in the insulator’s way, obstructing his pathway through the attic. As a result of these installation issues, areas near mechanical obstructions are often poorly insulated.
When an HVAC system is heating the home, attic bays 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. When an HVAC system is cooling the home, attic bays affected by mechanical obstructions 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 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:
Wire blockage
In a typical one-story, slab-on-grade home, the electrical panel is installed in the garage area. The electrical wires leave a single point in the garage and spread out to locations in the home. Most house plans locate part of the attic directly over or adjacent to the garage; wires run from the garage to the attic in a concentrated web. During installation, these wires interrupt the arc of blown insulation as it falls from the hose to the attic bays. Insulation ends up sitting on top of the wires, leaving the attic bays uninsulated.
Solution
Have the electrician elevate all wires at least 1' from the bottom truss chords or ceiling joists. Then, the insulator can blow under the wires. Another solution is to discuss wires with the insulator, and have the insulator blow insulation under the wires when entering the attic and then loft insulation over the wires when exiting. When using this method, make sure the insulation is blown to the correct depth and density.
ProTip!Make sure electrical wiring is installed in a neat and workmanlike manner.
Cause 2:
Ductwork blockage
In a typical one-story, slab-on-grade home, the HVAC system has to provide a lot of cooling. Because the home is relatively small, the HVAC contractor has to install the mechanical equipment in the attic with large diameter ducts that can completely fill truss webs. It's difficult to insulate behind and under these ducts. Another common problem is that the HVAC contractor may leave a duct sitting on the bottom truss chords or ceiling joists, instead of correctly supporting it above the framing. An unsupported duct prevents the insulator from getting blown insulation under and behind it.
Solution
Support all ducts every 4’above the insulation level. Then, the installer can blow insulation or install batts under them before the drywall stage. Exception: if California energy credits apply, make sure the ducts sit directly on the attic floor framing, so the installer can cover them with insulation.
Cause 3:
Platform blockage
A mechanical platform is a work area that supports and provides access to mechanical equipment in an attic. If the platform isn't high enough above the bottom truss chords or ceiling joists, the insulation can't be blown underneath it at the proper depth.
Framers sometimes build mechanical platforms at the minimum size needed to hold the HVAC system, which means some of the HVAC system components extend over the platform’s edge and block the insulator's path. Build mechanical platforms so they’re large enough to support the entire HVAC system.
Solution
Build the mechanical platform at a height that allows the full R-value of insulation to be installed underneath it. The framer can install mechanical trusses, which contain a member designed to support a mechanical platform. A mechanical truss leaves enough space between the bottom chord and the platform for a sufficiently deep layer of insulation to be installed underneath the platform. Or, the framer can install a platform at a height where the insulator can blow the required depth of insulation underneath it. Another option is to install a compact batt, which provides an equivalent R-value at a lower thickness, underneath the mechanical platform.
ProTip!It's helpful to not locate ducts or vents underneath a mechanical platform; they can make it difficult to install a sufficient layer of insulation under the platform.
