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 then 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, because the density is an unknown factor.
Measuring the thickness or depth can give you an idea of what the R value is.
TYPE / R-Value
|Insulation Type||R-Value per Inch Depth|
|Fiberglass batting||2.9 to 3.2|
|Fiberglass loose fill||2.9 to 3.2|
|Loose fill mineral wool||3.3|
|Extruded polystyrene board||5.0|
|Expanded polystyrene board||4.0|
Fiberglass or cellulose insulation that becomes damp, looses its ability to perform its intended function.
The insulating factor will need to be decreased and possibly reduced to zero.
Insulation that has been wet, should be completely removed, and replaced with new insulation.
Recommended R-values for Ohio Zones 2 & 3
- 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.
- Do not bury recessed ceiling lights in insulation, unless indicated on the installers tag attached to the light fixture that it is alright to do so.
- Insulation should be kept 2 inches back from metal flue pipe.
- The first six inches of insulation are the most cost effective, after that any added depth 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.
Current building regulations in our area require a minimum of 10″ of fiberglass in the attic and 3.5″ in the walls.
Most builders are now putting in a lot more insulation than was the norm in the early 2000’s. In a new home it is non normal to see between 16″ and 18″ in the attic. and Equally some of the custom builders and Green Energy Builders are installing 5.5″ of fiberglass in the walls (this requires 2×6 framing in the outer walls in place of the standard 2×4 framing).