Fiberglass Batts- Economical and widely available, this type of insulation resembles blankets made from glass fibers attached to a kraft-paper or foil backing; it has a proven performance record. In recent years, new types of glass fibers have been developed to reduce the characteristic skin irritation caused by the material. Fiberglass batts are sometimes wrapped in a plastic material to reduce skin contact during insulation.
   To attain its nominal R-value, however, fiberglass batts must fill wall or ceiling cavities completely. For this to happen, the batts must be sized to fill stud cavities precisely before being stapled in place. The glass strands, rather than the kraft-paper facing, should be notched to fit snugly around ducts, pipes and wires.
Cotton Batts- Now available in several southern states, itch free cotton batts made from recycled denim boast the same insulating qualities as fiberglass. Cotton batts are installed like fiberglass, but have less spring back, which means they need to be fluffed when unrolled, then given 48 hours to reach full expansion before installation.
Cellulose- Made from recycled newsprint treated with a fire retardant, cellulose can be blown in dry to fill wall cavities or applied using a wet-spray method. The loose fill will settle over time, so all cavities should be as tightly packed as possible during installation to compensate for future shrinkage.
Rigid Foam- When used as sheathing, the dense-cell structure of rigid foam panels creates a thermal break, which minimizes the impact of framing details on a wall’s R-value. Foam can be applied directly to framing as sheathing, provided the contractor first installs diagonal wind bracing at the wall corners. Research has shown that taping the seams between foam panels may eliminate the need not only for air barriers, but interior vapor barriers as well.
Spray Foam- The latest CFC-free spray-in-place foam is blasted directly into wall cavities, where it expands to 100 time its original volume. Expansion results in an excellent air-infiltration barrier. The foam fills cavities completely, leaving few gaps, even in cavities that contain complex mechanicals.

Sheathing
Not every wall needs sheathing. Two of the primary reasons for using it, however, are to provide lateral bracing and create a wind barrier.  Without it, those issues need to be addressed with other materials.
   Structural Sheathing has enough strength to stiffen a wall so that it withstands any reasonable stress caused by wind or seismic activity. This category of sheathing includes wood boards, plywood, oriented-strand board (OSB) and some fiber panels.
   The oldest form of structural sheathing is solid boards. Not used much today, solid sheathing cost about the same as plywood but requires more labor to install. Nailed diagonally to the studs of a wood-frame house, boards offer respectable resistance to racking and provide a solid nailing surface.
Plywood panels have exceptional bracing strength. When nailed to studs, ½-inch plywood produces a wall with lateral resistance six times greater than horizontal tongue-and-groove boards. Add glue to the panels, and that figure jumps by a factor of 5. Covering an entire home with plywood can get expensive. If you’re building in a relatively benign climate, you may choose a less costly material.
   Oriented-strand board (OSB) offers many of the advantages of plywood at about half price. If kept dry, it has good bracing strength and makes a suitable nailing base. Created from resin-soaked strands of small, fast growing trees, the product resists moisture but lacks plywood’s ability to dry our quickly. Consequently, OSB requires flawless application of interior vapor barriers and watertight siding, particularly in warm, moist climates.
   Fiber panels, an economical, lightweight product made from wood scrap, meet most requirements for racking resistance. The best fiber sheathing has waterproof asphalt coatings on both sides and along their edges. To ensure the panels function properly, the contractor must nail or staple fiber panels at close intervals, caulk all seams and apply additional sealant where panels meet rough window and door openings and protrusions through the home’s envelope.

Air Barriers
Exterior house-wraps consist of a woven polyethylene-based fabric. The wrap allows moisture to escape from inside the walls of your house while preventing wind from blowing through gaps in sheathing.
   In addition to their function as air barriers, house-wraps enable builders to get vulnerable sheathing material under cover quickly. Although the wrap isn’t water-proof, it has enough water resistance to fend-off occasional rain. It also filters ultraviolet light, protecting light-sensitive rigid foam panels.
   More important, because house-wraps allow water vapor to escape, plywood sheathing that gets wet can dry out through the house wrap. This feature can buy your builder extra time to finish roofing and close in the shell.
   Brooke Gilbertson of Gilbertson Construction, Lake Stevens, Washington, says, “We’re using house-wraps on every size project, even little additions and dormers. There’s no job that’s too small. A mistake I have seen is where the builder hacks and slashes the wrap and nails up a bunch of pieces. That’s no good. You need to leave sheets intact and make sure it penetrates all rough openings at least 1 inch on all sides.”
  Many of the most popular wraps come in 9-foot rolls, making them very easy to install.
Builders simply tack the material to the sheathing as it unrolls, then go back and cut an X over the windows and doors, the wrap should overlap all openings by a couple of inches.
   Like seams in vapor barriers, seams in air barriers should be taped. To protect against floor-level drafts, the fabric should be attached securely to the home’s foundation.