Insulating an Unheated Attic: A Comprehensive Guide

Insulating an unheated attic can be a daunting task, but it doesn't have to be. With the right knowledge and materials, you can easily insulate your attic and reap the benefits of improved energy efficiency and comfort. To begin, you'll need to measure the thickness of the existing insulation in your attic. If it's lower than the equivalent of R-30 (about 10 to 13 inches), you should consider adding more.

Before insulating, make sure to seal any air leaks and repair any necessary roof or other repairs. If your attic is located in a conditioned part of the house, remember to also isolate and hermetically seal access to the attic. Properly insulating cathedral-type ceilings will allow the roof temperature to be kept closer to room temperature, providing an even distribution of temperature throughout the house. Cathedral-type roofs should provide space between the roof cover and the roof of the house for adequate insulation and ventilation.

This can be achieved by using lattice beams, scissor frame frames, or sufficiently large beams. For example, cathedral-like ceilings built with 2 x 12 inch beams have space for standard 10-inch blocks (R-30) and ventilation. Cathedral-type ceilings without ventilation (warm roof design) are also an option. The warm roof design makes it possible to install more insulation in the roof cavity, since the need for a ventilation gap is eliminated. It is important that the roof cavity is fully sealed to the air of the conditioned space below to prevent moisture ingress and roof degradation. Insulating a slab in an existing house can be expensive and harmful, but if your house's slab is cold, it's possible to dig around the perimeter of the house and install insulation, usually a foam board.

In most parts of the United States, insulating the outer edge of a slab can reduce heating bills by 10% to 20%.If your attic has sufficient insulation and adequate air sealing, and your house is still drafty and cold in winter or too warm in summer, you will most likely need to add insulation to the exterior walls. If you're in the design phase of planning your new home, consider structural insulation panels, insulating concrete forms, and insulated concrete blocks. To save money on insulation in attics with sloped roofs, you may be able to install very thin, high-quality insulation around the edges of the attic (and any other critical area) and install different, thicker, more cost-effective insulation on the rest of the attic. If so, you'll most likely see spray foam insulation or the more traditional spongy fiberglass insulation. These materials literally have built-in insulation, and houses built with these products usually have superior insulating qualities and a minimal thermal bridge. When the attic roof touches the ground, around the edges of the attic, there is often not enough space for much insulation.

If the air distribution is in the attic space, consider insulating the beams to move the distribution to the conditioned space. Proper attic insulation can also keep the roof in better condition by helping to prevent ice accumulations and condensation. Loose-fill cellulose insulation or fiberglass slats are two popular options for insulating an unheated attic. Loose-fill insulation is usually less expensive to install than block insulation and provides better coverage when properly installed. The radiant barrier installation can be installed directly on the first layer of insulation (on the attic floor) or on the beams (on the attic roof).In addition, common mistakes made by homeowners who try to install attic insulation themselves, such as blocking ventilation grilles or using improper installation techniques, can be very costly to repair.

While you can get better performance out of any insulation simply by installing a greater thickness, The Department of Energy recommends that it be rated higher than R-30 in your attic insulation. Homes that have high ceilings or no attic space also have less space for insulation than a typical home. In new construction, consider construction techniques that provide both foundation structure and insulation, such as insulating concrete forms and insulating concrete blocks.

Victor Mosbarger
Victor Mosbarger

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