Only ceilings exposed to exterior temperatures need to be insulated.

If the attic is going to be insulated with batts, then you will first need to have the ceiling prepped with vapour retarder, and have all penetrations and joints sealed and fastened. It is common practice and a good idea to align your polyethylene, so that the over lapping joints line up over a piece of strapping, allowing for the joint to be fastened with staples as they are more durable than tape. Joints in the polyethylene running perpendicular to the strapping often can not be stapled, and therefore require the use of tape as the fastener. Once this is done, batts can be placed down flat in the attic and layered to achieve the proper R-value. (Example: 3 layers of R-20 = R-60). When installing more than one layer of batt insulation, subsequent layers should be run in alternating directions.

If the attic is going to be insulated with blown-in cellulose, rock/slag fibre, glass fibre, or other approved blown-in products, it is recommended to have a certified insulator install the product, but it is not a requirement. If the attic is going to be insulated with a spray-applied foam, a certified installer will also be required. In these cases, you are responsible for prepping the ceiling with vapour retarder and sealing any penetrations.

In existing homes it may be preferable to insulate the roof of an attic and make the attic a conditioned living space. This depends on the available space in the attic, its condition, and the intentions of the homeowner.