Before insulating or deciding whether to add insulation to your cathedral ceilings, first see our information about adding insulation to an existing house or selecting insulation for new home construction if you haven’t already.
Insulation Techniques

Cathedral ceilings must provide space between the roof deck and ceiling for adequate insulation and ventilation. This can be achieved through the use of truss joists, scissor truss framing, or sufficiently large rafters. For example, cathedral ceilings built with 2×12 rafters have space for standard 10-inch batts with R values of R-30 and ventilation.

Foil-faced batt insulation is often used in cathedral ceilings because it has a 0.5 perm rating, providing the permeability rating often required for use in ceilings without attic spaces. A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel.

If roof framing provides insufficient space for required insulation, higher insulation values can be obtained. You can attach furring strips, which allow additional insulation to be installed, to the underside of the rafters using high-density batts (high-density R-30 batts are as thick as R-25 batts and fit into 2×10 framing). You can also add rigid foam insulation under the rafters. Rigid foam insulation offers a resistance to thermal bridging through wood rafters. However, rigid foam insulation must be covered with a fire-rated material when used on the interior of a building. Half-inch drywall usually complies, but check with local building codes to be sure.

Source: U.S. Department of Energy

Air ducts supply conditioned air from your space heating and cooling equipment to your living spaces. They also return an equal volume of air back to the equipment to be conditioned again.

Ducts are typically made out of thin metal materials that easily conduct heat. Therefore, uninsulated or poorly insulated ducts in unconditioned spaces can lose through conduction 10%–30% of the energy used to heat and cool your home. The heating and cooling equipment then has to compensate for the heat loss and gain by conditioning additional air. This added conditioning raises a homeowner’s energy bills. In addition, when ducts lose heat through conduction, rooms served by long duct runs can experience “cold blow” during the winter because they usually have lower heating-supply temperatures.

Ducts in conditioned spaces experience minimal conductive losses and gains since they are exposed to indoor air temperatures. However, these ducts may also require some insulation to prevent condensation on duct walls and to ensure that conditioned air is delivered at the desired temperature.

Source: Department of Energy

Use construction adhesive and screws to attach rigid foam insulation to the attic side of the door. Pay special attention to the clearance between the insulation and the door frame and air sealing details. Adjust insulation levels or R-values to meet those recommended for your area and climate. Also, insulate and air seal the knee walls themselves for maximum energy efficiency.

Source: Energy Efficiency and Renewable Energy, U.S. Department of Energy

To ensure a tight fit between the stairs’ flat panel and the frame, weatherstripping or gasket material should be added either to the frame or panel. Latch bolts may be installed to help ensure a tighter seal.

To insulate attic stairs access, you can construct a lightweight, moveable box from rigid foam or fibrous ductboard to fit over the stairs from the attic side. Insulating kits are also available from weatherization suppliers or local hardware stores.

For air sealing, weatherstripping can be installed either on the hatch itself or on the inside of the trim or base where the hatch rests. Adding a latch bolt will help ensure a tighter seal.

After the trim or base is aligned to seal properly, insulation should be added to the attic side of the hatch. Rigid insulated sheathing is recommended. Cut the insulated sheathing 1/4 inch smaller than the hatch size to allow for clearance when moving the access panel. Apply 3 or 4 inches of insulation to the hatch with construction adhesive and screws.

As an added measure, glue the kraft-paper side of batt insulation to the top of the last layer of rigid insulation. Try to achieve the recommended R-value.

A home’s attic access, which could be an attic hatch, pull-down stairs, or a knee-wall door, often goes uninsulated. This gap in the attic insulation increases heat loss in the winter and heat gain in the summer.

These accesses also often aren’t sealed properly. A 1/4-inch gap around the perimeter of an attic access can potentially leak the same amount of air supplied by a typical bedroom heating duct.

Before insulating your attic access, you should first determine the recommended insulation R-value for your area and climate.
Attic Access Location

If you are constructing a new home or remodeling an existing home, carefully consider the location of an attic access. The location will affect how or whether the attic access should be insulated. If possible, locate the access in an unconditioned part of the house, such as a garage, covered patio, or porch. A garage location, where the vented attic is uninsulated, can eliminate the need for air sealing and insulation.

Before insulating or deciding whether to add insulation to your attic, first see our information about adding insulation to an existing house or selecting insulation for new home construction if you haven’t already.

Warning: if you think you have vermiculite insulation in your attic, there’s a chance it could contain asbestos. Don’t disturb it. Only insulation contractors certified to handle and remove asbestos should deal with vermiculite insulation.
Attic Insulation Techniques

Loose-fill or batt insulation is typically installed in an attic. Although installation costs may vary, loose-fill insulation is usually less expensive to install than batt insulation. When installed properly, loose-fill insulation also usually provides better coverage.

Before installing any type of insulation in your attic, follow these steps:

* Seal all attic-to-home air leaks. Most insulation does not stop airflow.
o Duct exhaust fans to the outside. Use a tightly constructed box to cover fan housing on attic side. Seal around the duct where it exits the box. Seal the perimeter of the box to the drywall on attic side.
o Cover openings—such as dropped ceilings, soffits, and bulkheads—into attic area with plywood and seal to the attic side of the ceiling.
o Seal around chimney and framing with a high-temperature caulk or furnace cement.
o At the tops of interior walls, use long-life caulk to seal the smaller gaps and holes. Use expanding foam or strips of rigid foam board insulation for the larger gaps.

* Install blocking (metal flashing) to maintain fire-safety clearance requirements (usually 3 inches) for heat-producing equipment found in an attic, such as flues, chimneys, exhaust fans, and light housings/fixtures unless the light fixtures are IC (insulation contact) rated. IC-rated lights are airtight and can be covered with insulation.

* Make sure insulation doesn’t block soffit vents to allow for attic ventilation.

* Check the attic ceiling for water stains or marks. They indicate roof leaks or lack of ventilation. Make repairs before you insulate. Wet insulation is ineffective and can damage your home.

Also insulate and air seal your attic access if it’s located in a conditioned part of the house.

You’ll want to properly insulate and air seal any knee walls—vertical walls with attic space directly behind them—in your home as well.

Finally, if you’re constructing a new home or remodeling, make sure any attic decking, which provides additional storage space or a platform for an HVAC unit or hot water tank, is raised above the ceiling joists to ensure proper insulation depth. The decking then should be installed securely to the top of the raised lumber after the insulation has been installed.
Other Considerations

If you live in a hot or warm climate, you might consider installing a radiant barrier in your attic along with the insulation.

Source: U.S. Department of Energy

The amount of insulation you need depends on the climate, the part of the house, and the type of heating and cooling systems (gas, oil, or electric) you have. Your attic is the best place to start. The Department of Energy has an online calculator to help you decide what’s right for you. Visit the Zip Code Insulation Program website. For more information about insulation, visit the Energy Savers website at www.energysavers.gov, or call 1-877-EERE-INF (1-877-337-3463).

No matter where you live, your home will be more comfortable and cost less to heat and cool with the right insulation. That could mean more money in your pocket all year round.

Unless your home was designed with energy efficiency in mind, adding insulation can be a good way to save money. Most older homes were built without much insulation, which can mean high energy bills. Even if your home is new, more insulation can pay for itself in a few years and increase your home’s resale value.