Attic

INSULATION R-VALUES

The insulating value of insulation is given as an R-value.  The R is for resistance. The greater the resistance the material has for disallowing the transfer of heat, the greater the insulating R-value.

Insulation values are approximate; the R-value can depend on the installation and change over time as the insulation becomes compacted,  loosing some of its effectiveness. 

The true R-value of "already" installed insulation cannot be determined by measuring the depth of the insulation. Measuring the thickness or dept can give you an idea of what the R value is.

TYPE / R-value (rated per inch in thickness)

Fiberglass Batts 2.9 to 3.2

Fiberglass Loose fill 2.9 to 3.2

Loose fill mineral wool 3.3

Cellulose 3.2

Polystyrene Board, Extruded 5.0

Polystyrene Board, Expanded 4.0

Foam 3.9

NOTE: Fiberglass or cellulose insulation that becomes wet, looses its ability to perform its intended function. The insulating factor will need to be decreased and possible reduced to zero. Insulation that has been wet and should be completely removed, and replaced with new insulation.

Adding Insulation?
1. To an older house with knob and tube wiring, this type of wiring cannot be encapsulated (buried) in any type of insulation. knob and tube wiring that in buried in insulation will overheat and may cause a fire.
2. Do not bury recessed ceiling lights in insulation, unless indicated on the installers tag that it is alright to do so.
3. Insulation should be kept 2 inches back from metal flue pipe.
4. The first six inches of insulation are the most cost effective, after that any added dept will have a progressively longer pay back time.

Need to add insulation to an attic with limited headroom, consider adding radiant heat barrier (an aluminum foil blanket). This product reflects 97% of the heat back into the building during the heating season and 97% of the incoming heat away during the summer. (Supplier in Dayton)

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