Installing Insulation

Ceilings
Adding insulation to an unheated attic is usually straightforward. If there is no attic flooring, either loose-fill insulation can be blown in or fiberglass batts can be laid between the joists. If existing insulation comes up to the top of the joists, an additional layer of unfaced batts can be added on top. Center these over the joists so they cover gaps in thefirst layer. Insulation should be even and should cover corners. Also insulate and weatherstrip the access door or hatch. If access to the atticis limited, blown-in insulation will work best.

To ensure proper air circulation, make sure the insulation does not block vents. For roof vents, 12 inches of clearance is usually recommended. For eave vents, little clearance is necessary, as long as the vents are not obstructed. Keep insulation away from recessed light fixtures, and otherfixtures that emit heat, to avoid fire hazards. Some newer recessed lightsare IC (insulation contact) rated and can safely be buried by insulation.

Unless the attic already has some insulation, add a vapor retarder when you insulate. Most batts and blankets have a kraft paper vapor retarder on one side. This prevents excessive moisture from condensing in the insulation, which could reduce its effectiveness. The vapor retarder must be installed on the warm side of the insulation (face down in cold climates, face up in hot climates), or it can do more harm than good. When additional insulation is placed over existing insulation, do not install a vapor retarder, as it may trap moisture in the insulation underneath.

Do not store anything on top of ceiling insulation. When insulation is packed down, it tends to lose its effectiveness. Insulating a sloped cath- edral ceiling can be much more difficult. There is little room between the ceiling and roof, and the cavity is difficult to access. The best method is to add rigid foam on the outside when reroofing. Another method is to drill holes in the drywall from the inside and blow insulation into the joist cavities. However, moisture can accumulate in the insulation if there is no ventilation in the cavity. Some people go so far as to build an attic and put on a new roof, so that there's more room for insulation.

Walls
Finished wall cavities are best insulated by an experienced contractor. The installer must drill holes in the sidewall and blow the insulation into each cavity between the studs.

For new construction, there are more options. Batts, wet-spray cellulose,or loose fill blown in through a cover over the studs can be installed between the studs, and rigid board insulation can be put up before the siding is installed. Re- siding also presents a good opportunity to put rigid board insulation between the old siding and the new.

When installing batt insulation, don't compress it to fit behind electrical boxes-this will create areas around the boxes where the insulation is not fully expanded. Cut the insulation around any obstructions. Follow manufacturer's recommendations on stapling the facing to the studs.

Some people do use compressed batts for the whole wall, though. For instance, you can install a 6-inch R-19 fiberglass batt into a 3 ½ inch stud cavity (which would normally take an R-13 batt). The compression will reduce the R-value to about R-17. This technique is especially useful in older homes, where 2 x 4 studs are truly 4 inches deep (modern 2 x 4s are only 3 ½ inches deep).

Basements
If the basement space is unheated, it may be best to insulate between floor joists (basement ceiling) instead of around the foundation (basement floor and walls). Unfaced fiberglass batt insulation, supported from below with metal supports or wire mesh, can do the job. If you insulate above an unheated basement, also insulate any ducts or pipes running through this space (especially in cold climates where pipes might freeze), since the space will become colder in winter.

If you choose to convert an unheated basement into insulated living space, the simplest method is to build 2 x 4 frames against the concrete foundation walls, insulate with batts or blankets, and cover with drywall. Another method is to attach wood furring strips to the walls by nailing or bonding. The insulation can then be stapled or tacked into place. Drainage problems may need to be addressed to ensure that no exterior water leaks into the basement, and the concrete should be treated with water seal or vapor barrier paint.

Benefits of insulating the basement walls and floor can include decreased condensation (which can help prevent mold and mildew), reduced energy losses from ducts running through the basement, and reduced risk of pipes freezing in winter.

Slab Floors
Insulating a slab foundation requires digging around the foundation at least 6 inches down. Attach rigid foam board; add a protective covering,such as fiberglass panels, treated plywood, or cement coating; then fill in and compact the soil. Although the slab will be insulated only at the edges, this is where most of the heat loss occurs.

Crawlspaces
If a crawlspace is ventilated, insulate the floor above it. Batts are generally installed between the floor joists and must be well supported so they don't sag or fall down. The batts should touch the floor boards continuously and should not be compressed. This is easier said than done. Insulating can be difficult while lying on your back, and getting the batts to stay up against the floor is a challenge. Common methods include using wire mesh (chicken wire) fastened to the joists under the batts, metal supports held up by tension between the joists, or wood lath supports attached perpendicular to the joists 18 inches apart. Use batts that are the exact thickness of the floor joists. When you insulate the floor above a crawlspace, don't forget to insulate all ducts and water lines running through the space.

Insulate crawlspace walls only if the crawlspace is dry all year, the floor above is not insulated, all ventilation to the crawlspace is blocked, and a vapor barrier (for example, 4- or 6-mil polyethylene film) is installed on the ground to reduce moisture migration into the crawlspace. Insulation batts can be fastened to the sill plate and draped down the wall. Because the insulation will be exposed, be sure to use either an unfaced product or one with the appropriate flame-spread rating. If you live in a very coldregion, you should continue the insulation over the ground (on top of themoisture barrier) for about 2 feet from the wall.

• Insulation 101: How It Works
• Type of Insulation
• Figuring Out What You Need
• Installing Insulation
• Doing it Yourself