Every home needs insulation. Whether or not you install the insulation yourself depends on the structural design of your house and the type of materials used in its construction.
Placing insulation in the attic floor is usually easy, requiring only laying the material between the parallel joists of the frame. Be careful about where you step in the attic. Walk only on the joists so that you won't fall through the drywall ceiling. You may need to place walking boards across the tops of the joists to make the job easier. Remember that it is important to seal up air leaks between your living space and the attic before adding insulation to your attic.
Bear in mind that insulation placed between joists, rafters, and studs does not retard heat flow through the exposed frame. This heat flow is called thermal bridging and is especially important in houses with metal frames or joists. In attics, thermal bridging can be reduced by adding sufficient loose-fill insulation thickness, or cross-installed batts, to cover the wood or metal frame as much as possible. In some houses with low-pitch roofs, it is difficult to gain access to all of the attic floor, so blowing equipment may be needed to place insulation in relatively inaccessible areas. In most attics, it is easier to get complete coverage with blown-in insulation. It is best to hire an insulation contractor for this job.
In existing buildings, installing insulation in the cavity of exterior walls is difficult. It usually requires the services of a contractor who has special equipment for blowing loose-fill insulation into the cavity through small holes cut through the sidewall, which later are closed. It is sometimes feasible to install rigid insulation on the outdoor side of masonry sidewalls such as concrete block or poured concrete. When new siding is to be installed, always consider adding thermal insulation under it. Generally, the services of a qualified contractor are needed to make such installations.
The homeowner can often insulate basement or crawlspace walls, or floors over unheated areas, using rigid insulation or batt insulation. Sprayed-on insulation products are also available for these locations but would require a qualified contractor. If you insulate a floor above a crawl space, all ducts and water lines running below the insulation should be insulated as well.
Insulate crawl space walls only if the crawl space is dry all year, the floor above is not insulated, all ventilation to the crawl space is blocked, and a vapor retarder (e.g., heavy-weight polyethylene film) is installed on the ground to reduce moisture migration into the crawl space. The "Builder's Foundation Handbook" published by the US Department of Energy is a complete guide to foundation insulation, including basement, crawl space, and slab insulation.
Adding thermal insulation to the ceiling or walls of a mobile home is complex and usually requires installation by specialists. However, it is often possible to add floor insulation to such a home, just as you would for any other type of house.