When it comes to insulating an attic in a cold climate, blown cellulose insulation with an R-value of 49 is the most effective option. This type of insulation is effective at all temperatures, but it may be more efficient in colder climates. If you live in the northern parts of the country, it's important to consider insulation for a cold climate. The most cost-effective and straightforward way to insulate your attic is to rope, seal your windows, and seal any penetrations.
To determine if you have enough insulation, measure the thickness of the insulation. If it's lower than the equivalent of R-30 (about 10 to 13 inches), you should think about adding more. Before insulating, make sure to seal any air leaks and repair any necessary roof repairs. If your attic is located in a conditioned part of the house, remember to isolate and hermetically seal access to the attic.
Cathedral-type ceilings 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. A warm roof design is also an option for cathedral-type ceilings.
This design eliminates the need for a ventilation gap and allows for more insulation in the roof cavity. However, it's 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%.
Loose-filled fiberglass attic insulation still experiences convection, but not as much as it used to. Make sure to also insulate and air-seal any knee walls (vertical walls with attic space directly behind them). In northern parts of the country (5 zones), EnergyStar recommends insulating the attic at a distance between 49 and 60 R$. A widely publicized study conducted by Oak Ridge Laboratories in 1991 said that loosely filled fiberglass insulation for attics lost much of its insulation value once temperatures dropped below 20 degrees, making it an inferior product compared to cellulose.
However, if you check with the North American Insulation Manufacturers Association, they will assure you that fiberglass or mineral wool are definitely your best option for insulating the attic. In most cases, a basement with insulation installed on its exterior walls should be considered a conditioned space. Slab foundations with interior insulation provide more resistance to termites, but some builders in the southeastern United States have even reported termite infestations through foam insulation in contained slabs. If you live in a hot or hot climate, consider installing a radiant barrier on attic beams to reduce heat gain in summer. A ventilation deflector must be installed between the insulation and the roof cover to maintain the ventilation channel. Shredded and recycled cellulose paper with added boric acid for insect control and fire resistance offers a better attic insulation option than blocks. Loose-fill fiberglass seems to dominate attic insulation in newly built homes and has an R-value of approximately 2.5 per inch.
Check out this post on how to install blow insulation, which is an insulation technique that is extremely easy to do yourself. These materials literally have built-in insulation, and houses built with these products usually have superior insulating qualities and a minimal thermal bridge.