According to ENERGY STAR (r), new insulation can be installed over existing insulation "unless it is moist." Moisture can be trapped by a vapor retarder placed on top of or between layers of insulation. Any existing batt or roll insulation in the attic should be facing the drywall floor or have no facing at all. If it does, then some form of vapor barrier must be put over it.
If you are installing insulation as part of an energy-efficiency upgrade project for your home, then it's important to use certified insulation, which can help reduce your heating and cooling bills. Certified insulation is labeled with two numbers that tell you how effective it is at stopping heat flow and reducing noise pollution. For example, one common type of certified insulation is R-13. That means it will cut your heating bill by 13 percent and your cooling bill by 12 percent when used to insulate an average-size room. You can check the certification label before you buy.
When replacing old insulation, make sure to select a product with an equivalent R-value or higher. This will ensure that you're keeping up with what's needed for adequate insulation performance. Be careful not to install too much new insulation, as this can lead to high utility bills due to insufficient air circulation inside the house.
Installing insulation is easy work for any home improvement project.
Any new batt or roll insulation put over existing attic insulation must be free of vapor retarders (face). This moisture can cause mold and mildew growth in the attic.
If you're adding additional inches of insulation, do it in at least two stages. If you wait until your insulation is cold, it may be too late - you'll need to add more insulation! Insulation takes time to warm up and reach its full capacity for storing heat. You want to make sure you have enough warmth stored up during the coldest parts of the year.
The best time to add insulation is before you get hot in the summer or cold in the winter. Then it will be ready to go when you need it most.
Here's how to double your insulation job: Cut a length of fiberglass batting at least as long as your ceiling height. Place a layer of loose insulation on the floor of your attic (try to avoid having any fibers touch each other or they might both melt if exposed to heat). Spread the fiberglass batting out across the floor, making sure there are no holes or gaps where air can get in. Repeat this process with another layer of insulation and more fiberglass batting. The final layer should be covered completely with fiberglass batting.
You once mentioned nailing down plastic sheets over rolls of insulation. A vapor barrier, in any event, always faces the hot side, therefore it would never be installed on top of batt insulation in an attic. It might be used as a protective covering for cold-side insulation if there is no other way to protect the insulation from moisture.
The only time I have ever seen this done is with bubble wrap. They will cut the bubble wrap to size and then nail it up over the insulation. This is not recommended for several reasons: first of all, because it is not a good thermal break; secondly, the nails may become exposed and allow water into the wall cavity; finally, the plastic may come loose over time.
So the answer is yes, you can cover the insulation with plastic, but it isn't recommended because it doesn't provide much protection against heat or moisture damage and it could also cause some problems if it comes loose over time.
After you've installed the insulation, you may convert your attic into useful storage space by covering the floor with plywood. It will also make the attic a safer area to stroll in. Covering the floor will help the insulation hold its shape and keep it in place while allowing air to circulate underneath it.
Attic insulation is very important because without it, you would be wasting energy by heating or cooling an empty space. The more insulation there is up here, the less heat or cold will need to be brought down below.
You should cover your attic with plywood only if you plan to use it as storage space. Otherwise, you will be defeating the purpose of adding insulation in the first place. Insulation is designed to keep out heat and cold, so making a storage space that people can walk through will reduce its effectiveness.
Plywood is the best choice for covering an attic because it's affordable, easy to work with, and durable. It can also be painted if you want to add color to the room. Just make sure that whatever color you choose goes with the rest of your house and isn't too dark or light. If you go with a darker color, then you will need to think about installing some additional lights up here or there will be some darkness when you walk around.