The first thing you need to do is establish how much insulation is needed in an attic space in your part of the country. For the sake of simplification, we will use the northeast as an example. Contact your local building department, building supply dealer, or a local general contractor to determine the depth needed in your area. We will use the northeast as an example with an installation of 12 inches of fiberglass insulation. While several types of materials may be used we will use fiberglass batts as the materials are easily available and do not require special tools. This is important if you want to do it yourself.
First, measure the distance between the ceiling joists in the attic. These are the horizontal wood frame members that you are standing on when in the attic (attic floor, the ceiling of the room below). Most of the ceiling joists are either 16 inches or 24 inches on center. The fiberglass batt material you obtain will be designed for installation within this space as these are the two general options. Fiberglass batt is a type of fiberglass insulation that has been manufactured in sections precut at eight feet long or in rolls. Measure the width and length of the attic space, then multiply the distance to determine the square footage needed.
There are two different methods of installation, a single depth of 12 inches or a two layer system, with a first layer depth of 6 inches with another layer of fiberglass 6 inches to be placed perpendicular on top of the first layer. The second method is the best but the first is sufficient. Wear a dust mask, gloves and old clothes. Fiberglass can be quite irritating to skin and everyones tolerance if different. Fiberglass tends to give off particles easily and the material should be cut where these particles can be controlled. As you proceed, place the fiberglass batts within the cavities between ceiling joists and when needed use a utility knife to cut the material to fit as needed. To cut, firmly push the insulation against a board or other cutting surface and draw the utility knife across the fiberglass and the cut is established. The insulation may be cut length wise or or width wise easily with this method.With the first method, fill the spaces with the insulation until complete.
With the second method, fill the spaces between the ceiling joists first, and then place the second layer perpendicular across the entire space until complete. Ventilation of an attic space is also important, and many different types of attic ventilation are used. Remember that while you are insulating, do NOT block off any spaces that allow air flow at the perimeters of the attic space. This is a ventilation source at the roof overhangs, the lowest point of the attic perimeters. Depending on attic design, air must flow from the exterior at these spaces to other ventilation sources at upper attic sections. Purchase air baffles at the insulation dealer and place the baffles between the roof sheathing and insulation at the perimeters.
