Insulation of a structure is another important factor when considering the comfort of the occupants and energy costs. “R” value refers to the resistance of the flow of thermal energy through a material at 70 degrees F; the greater the “R” value, the better its insulation characteristics. The following are approximate “R” values per inch for the material indicated:
- Loose blown-in-fiberglass - 3.0
- Fiberglass Batts/Rolls - 3.2-3.6
- Mineral Wool - 2.7-3.2
- Perlite- 2.6
- Vermiculite - 2.1
- Foam - 4.5-6.2
- Cellulose - 2.8–3.5
Cellulose and rock wool insulation have much the same insulation qualities as fiberglass, however, they are prone to settling over time, thereby reducing their effectiveness. Moisture in the insulation also reduces its effectiveness, because it changes the density of the insulation.
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With cathedral type ceilings, there should be at least a 1-2 inch space between the top of the insulation and the bottom of the roof sheathing for ventilation purposes. Another problem to watch for and caution against is covering soffit vents with insulation, especially the blown-in type. Properly installed baffles will eliminate this concern.
Adding attic insulation may be done in different ways. If the insulation already installed is blown-in type, fiberglass batts/rolls of fiberglass may be laid directly on top. If the space between the trusses/joists is filled, and batts/rolls are used, they should be laid perpendicular to the trusses/joists. It is not recommended that heavier type insulation be installed over top of a lighter type (e.g. cellulose over fiberglass, as it will compress the lighter insulation and reduce its effectiveness).
Attic doors should be weather-stripped and insulated on the attic side using fiberglass batts, foam sheet, etc. If a vapor barrier is used, it should be against the door or warm side. If the structure has a walk-up attic stairway, the walls should be insulated as well as under the steps, keeping in mind the vapor barrier should always face the heated side of the wall/ceiling. For those attics with pull-down stairs, weatherstrip the door (all 4 sides), consider constructing a cover over the opening in the attic, and insulate the box.
Recessed light fixtures are not to be covered with insulation unless specifically designed, manufactured and labeled as IC (insulation contact), but rather should have a 3-inch clearance on all sides. Covering such fixtures with insulation could cause overheating of the fixture and create a fire hazard.
In crawl spaces, insulation should be installed between the joists and against the band joist, completely filling the cavity. The insulation should be at least 5 ½ inches thick, have a vapor barrier facing the heated area, and be held in place by friction, staples or retaining wires.
Removing an electrical cover plate on an exterior wall and fishing beside the electrical box with a hook can sometimes determine whether or not insulation was installed in the walls. However, the quality of the insulation job can only be determined with infrared photography of the structure. Benefits versus costs of installing wall insulation after construction are considered minimal at best.
Urea Formaldehyde Foam Insulation (UFFI) is a foam insulation that is usually white to pale yellow in color, it is soft, and crumbles very easily to baby powder consistency. There was considerable excitement about this insulation in the past due to emission of formaldehyde gases, which could cause respiratory problems and allergies. The formaldehyde was used as a binder, as has been the case with some glues/adhesives for decades. UFFI use has been discontinued. UFFI was generally installed during the 1973-1983 time frame. Note: It takes 2 to 5 years for the formaldehyde to 'offgas', depending on the relative humidity in the area and exposure to the sun. The higher the RH, the faster it would offgas.