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Insulation of a structure is another important factor
when considering the comfort of the occupants and energy costs. The “R” value referred to when speaking of insulation signifies
the resistance to 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:
|
Insulating material |
R value |
|
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.
There should also 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.
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).
Recessed light fixtures are not to be covered with
insulation, 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.
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.
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 is not now being used.
Use of UFFI was generally 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.
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General
Heating and Air Conditioning Windows
and Doors Water Heaters
Recommended Conservation Measures
Common Defects
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