The purpose of insulation that lays along the ceiling joists (the attic floor) is to keep the home's rooms cool in summer and warm in winter. The walls and ceiling of an unfinished attic do not need to be insulated, but it's important to have vents in the roof. A finished attic is treated like any room in the home.
It's usually not recommended to have insulation in both the ceiling and floor of an attic because this creates a ``dead air space'' which can be prone to moisture problems. What happens is that moisture from the house can move up into the attic.
When a home has inadequate insulation in the attic, a lot of air is lost through the roof. Energy bills skyrocket, and it's impossible to keep the temperature in the house regulated.
While loft insulation is an effective way to improve energy efficiency and reduce heating costs, over-insulating can lead to several potential issues. Firstly, over-insulation can lead to poor ventilation in the attic, which can cause moisture buildup and increase the risk of mould growth.
Also, when laying down additional insulation, work from the perimeter toward the attic opening. Never lay insulation over recessed light fixtures or soffit vents. Keep all insulation at least 3 inches away from recessed "can" lights, unless they are rated IC (Insulated Ceiling).
Insulation is graded by its R-value—the higher the R-value, the greater the insulating power. If you live in a mild climate, your attic should have a minimum grade of R-38, or about 13–14 inches of insulation. If you live in a colder climate, R-49 is the minimum recommendation, or about 16–18 inches of insulation.
The recommended level for most attics is to insulate to R-38 or about 10 to 14 inches, depending on insulation type.
Can I put plywood over insulation in the attic? Yes you can install plywood subflooring directly over the floor joists and insulation on your floor. You need to install rigid insulation boards on top of the attic flooring joists and then install plywood over the top.
If your attic has little or no existing insulation, you'll want to install an R-38 rated material. If your attic has 2-3″ of existing insulation, you'll want to install an R-30 to achieve a total of R-38. If your attic has 5-6″ of existing insulation, you'll want to install an R-19 to achieve a total of R-38.
Looking across your attic, if the insulation is level with or below the attic floor joists, you probably need to add more insulation. If you cannot see any of the floor joists because the insulation is well above them, you probably have enough, and adding more insulation may not be cost-effective.
Cons of Blown-In Attic Insulation:
If your attic has a moisture problem or experiences water leaks, the insulation can become damp, leading to mold growth and reduced effectiveness. Requires Professional Installation: While it may seem simple, blown-in insulation must be installed by experienced professionals.
Hot air rises, just like your energy bill will do if your attic is poorly insulated. A poorly insulated attic can result in 25% heat loss in fall and winter—that's 25 percent of your average heating costs going toward energy that won't even heat your home.
Overall, the second layer of insulation plays a crucial role in improving insulation performance, reducing heat loss, and maintaining a comfortable and energy-efficient living space.
As energy efficiency moves to the forefront of priorities for homeowners and buyers, attic insulation has become increasingly important. Homes that lack adequate insulation in attics are at risk for a range of expensive and irreversible impacts like water damage and heat or cold air loss.
IS IT OK TO PUT INSULATION BETWEEN ROOF RAFTERS? Insulating between roof rafters is not only okay, but it is often recommended as a way to minimise the use of headspace while maintaining comfortable indoor temperatures.
In Most Cases, Attic Insulation Does Not Need To Provide A Vapor Barrier. The good news is that blown-in insulation should not need a vapor barrier.
In hot, humid locations, it may also be advisable to construct unvented rather than vented attics to help reduce the entry of moisture-laden air into the attic. In hot, humid locations, the outside air is likely to be more humid than the inside air.
In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below.
On average, you can save up to 20% on your home's heating and cooling costs or up to 10% on its total energy costs by adding insulation to attics, floors, crawl spaces, and accessible basement rim joists, and by reducing unwanted air leaks all around your house.
The short answer, yes, insulating the attic is an effective way to keep your home cooler during the summer months. While it's a given that the insulation in your attic will keep the home warmer during the winter, it isn't immediately obvious that insulation can also help to keep the home comfortable during the summer.
The bottom line is the old insulation needs to be removed because it hinders the airflow into the attic, it can promote mold growth, and it is dirty.
Blown fiberglass insulation scores an R-value of 3.2 to 3.8, making it slightly less likely than rolled fiberglass to prevent the flow of heat into and out of your house. That being said, though, blown fiberglass insulation isn't meant to cover huge areas like rolled fiberglass insulation.
Foam boards
Easy to install and relatively inexpensive, foam boards are another insulating option. They are usually made of polyurethane, polystyrene, or polyisocyanurate. Sheets of foam can be cut to fit tightly between wall studs or attic ceiling joints.
You can use faced or unfaced batting when installing between the roof rafters of finished attic spaces. When using paper or plastic batting insulation, that moisture barrier should face outward toward the attic space. Even if the attic space is unheated, it's typically warmer than the outside air in winter.