Flat Roof/Attic
The attic/cockloft is one of the largest sources of potential heat loss in a home and often one of the most neglected areas when it comes to insulation, especially in older brownstones & row houses. If your top floor is hot in the summer or if the furnace can't keep up in the winter, chances are your roof needs more insulation.

Wall
Whether lathe & plaster or drywall, the walls of your home are arguably the most beneficial and important areas to insulate.

Ceiling/Floor
Insulate ceilings when you wish to acheive separate zoned heating. Floors over unheated spaces such as parking garages should always be insulated.

Crawlspace/Basement
An uninsulated crawlspace/basement is a major source of energy loss and contributing factor to thermal inefficiency.

New Construction/Renovation
Cellulose can be spray applied damp or installed into exposed framing w/ netting.

Air Sealing
A "leaky" house causes higher energy bills and allows excess moisture and contaminants to enter the home. Air sealing a house increases comfort by reducing the drafts in a house and by reducing the cycle time that your heating and cooling systems are going to run.