Insulation: Attic

The home's designer should indicate exactly where to install insulation in the attic and define the insulation strategy on the drawings. It's also important to determine whether blown insulation, batt insulation, or a combination of blown and batt insulation should be used, given the architecture of the home and the required attic R-value.

The designer should plan the eave framing to provide as thick a layer of insulation as possible at the eaves. If the insulation layer isn't thick enough at the eaves, the deficiency can reduce the total amount of attic insulation by 15 to 20%, depending on size and slope of the roof. To ensure a sufficient layer of insulation will be installed at the eaves, the designer should specify energy or raised-heel trusses. Energy and raised-heel trusses allow insulation to be installed to the required thickness.

Some areas are difficult for the insulator to reach after drywall is installed. Have a plan for insulating these areas. In most cases, the best strategy is to install batts in these areas before the drywall stage. Consult with the insulator on the strategy for insulating:

• Sloped ceilings
• Raised ceilings followed by dropped hallways
• Changes in ceiling height or roofing dimension
• Transitions from mechanical to conventional trusses
• Gables, bays, and bows that are framed in
• Gables, bays, and bows with low ceilings
• Areas not visible from the attic access

Give the insulator the tools needed for a successful installation. Have the framer position continuous braces (rat runs) in a way that allows the insulator to walk on them through the attic, instead of balancing on the truss chords. Also, provide work lights for the insulator, so remote areas of the attic are visible.

After the attic is insulated, it isn't unusual for a mechanical trade to enter the attic and shift insulation out of place to service a duct, register, or other component. Once insulation is moved, it can be almost impossible to replace it properly. In most cases, planning ahead and providing proper access can prevent trades from having to move insulation. At the attic hatch, provide a framed step-off point and a walkout to any mechanical equipment, so trades, as well as inspectors, service technicians, and homeowners, can walk into and through the attic without putting their feet down into the insulation. If a trade has to move blown insulation, reinsulate the affected attic bays with blown insulation or batts. If batts are moved, make sure they're replaced.

The eave areas are lower than the rest of the attic, so it can be challenging to properly insulate them. To ensure a sufficient layer of insulation will be installed at the eaves, it's best to build a high 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.

Have the electrician elevate all wires at least 1' from the bottom truss chords or ceiling joists, so the insulator can blow under the wires. If the electrician must install wires near the attic floor, discuss the 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.

Make sure the HVAC contractor supports 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.

Build the mechanical platform to 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 under the platform. Or, the framer can install the platform at a height where the insulator can blow the required depth of insulation underneath it. If the mechanical platform has to be close to the attic floor, install compact batts under the platform. Compact batts provide an equivalent R-value at a lower thickness. It's helpful not to locate ducts or vents under a mechanical platform; they can make it difficult to install a sufficient layer of insulation under the platform.

Attach baffles to the exterior faces of the top plates, so the insulation can completely 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 they extend up the roof interior at least 6" beyond the insulation level.

If installing blown insulation, make sure end dams of sufficient height are installed at all areas where blown insulation needs to be contained, such as at slopes, hatches, and garage wall separations, before installing drywall. Keep in mind that blown cellulose isn’t as dense as blown fiberglass. Cellulose has to be blown at a greater depth than fiberglass, so higher end dams are needed. For instance, if an 8.5" end dam is needed for fiberglass, then a 10" end dam may be needed for cellulose.

It's important to cover the eave areas with end dams. One method is to extend the wall sheathing up the eave; this 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, make the end dams higher to protect the higher eaves.

If installing blown insulation, place all depth gauges so they’re facing the insulators as they walk through the attic. Depth gauges near the attic hatch should be oriented so the insulator, inspector, and site supervisor can read them as they enter the attic. At steps in ceiling height, place depth gauges at both levels of the step before drywall is installed. At slopes, place depth gauges at intermediate levels of the slope. The industry guideline for depth gauges is to install one depth gauge every 200 square feet, but using more depth gauges can help to ensure proper depth in stepped and sloped areas.

Before installation begins, make sure the insulator has brought the correct number of bags to the job. Check the insulator’s bag count using the coverage chart. A coverage chart provides an insulator with the bag count, density, and thickness needed for the desired R-value over a given attic area. During installation, confirm that the correct number of bags is being blown into the attic bays.

Make sure the insulator blows parallel to the trusses or ceiling joists. Also, have the insulator walk all the way into remote areas of the attic, as well as around and behind framing obstructions, to install insulation in the attic bays.

Blowing insulation takes at least two people. The team member monitoring the hopper has to keep the insulation at a certain level in the hopper, so the hose can supply the right density. Check the hopper at least once during the attic job. If the picker inside the hopper is visible, the insulation level is too low. The insulator should follow the blower instructions, as well as the blowing chart for the insulation. A site supervisor can mention to the insulation foreman that the hopper level will be checked occasionally in order to ensure that the insulation layer will be sufficiently dense.

When the insulator brings materials into the home, check to confirm that the batts are attic batts. 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. Make sure the installer bounces each batt on its side, so it fully recovers its thickness. Then, measure the batt’s recovered thickness. 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 the batts will 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 using 4' batts, make sure they’re touching snugly end-to-end. Also, confirm that the facing overlaps 1/2".