Understanding Insulation

By Author: New Jersey Home Inspector Michael Del Greco
Total Articles: 21
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Understanding Insulation

Submitted by: Michael Del Greco, New Jersey Home Inspector Lic GI 0121, President of Accurate Inspections, Inc, a New Jersey home inspection company

One of the ways a house loses and gains heat is through conduction. Conduction is the movement of heat through solid objects, such as walls, the ground, floors and ceilings. Heat always moves toward the cold, trying to equalize the temperature, and does move through solid material. Heat inside a warm house will always try to escape and, in the summer, the heat outside tries to get in.


Insulation in floors, ceilings and walls is helpful because it traps tiny pockets of air that retard the transfer of heat. Insulation won\'t stop heat entirely, but will slow it down.


Insulation\'s effectiveness is indicated by its ``R-value,\'\' which is its ability to resist heat flow from warmer to cooler areas. The higher the R-value, the more effective the insulation. It is important to remember that a material\'s insulating ability is based on R-value, not thickness.


Types of Insulation


Batts and blankets — ...
... Fiberglass. The R-value per inch is 3.1 to 3.5. It is best suited for standard joists, studs or rafter spacing in attics, walls and the underside of floors.


Loose fill — Cellulose, fiberglass and vermiculite. The R-value per inch is 2.2 to 3.7. It is best suited for non-standard spacing, infill of block walls and when spacing between joists that have obstructions.


Rigid board — Polystyrene, polyisocyanurate, urethane and bead board. The R-value per inch is 3.5 to 5.5. It is best suited for basement walls, foundations, exterior walls, interior walls and cathedral ceilings.

Where to Add Insulation to a Home

1. Living area ceilings below an unheated attic.

2. Living area floors above unheated basements, crawl spaces, garages and open porches.

3. Uninsulated exterior frame walls.

4. Between sloping rafters. Be sure to leave an air space for ventilation between the insulation and the roof sheathing. (Select insulation accordingly.)

5. In the back of band or header joists around the perimeter of the basement.

6. Basement walls when below-grade space is finished for living purposes or when the basement doesn\'t enclose a fossil-fueled furnace or boiler (gas/oil).

7. Basement walls where the above-grade exposure exceeds 50 percent of the interior wall surface.


When adding insulation in the attic, keep at least 1 1/4\'\' space between the insulation and the sheathing to allow air from the soffit/eave vents to flow to the ridge and/or gable vents.


The Cost to Add Insulation

You can expect to pay 65 cents to $1 per square foot for insulation, including labor and materials.


In the attic, a contractor will install about 9\'\' of insulation. If you have a 1,000-square-foot attic at an insulation cost of $650 to $1,000, you can expect savings of $125-$200 per year, depending on the climate. Your payback would occur in five to six years.


Walls — Insulating walls is generally an economic loser. Also, the walls are much more difficult to insulate. It requires drilling holes, filling walls and using an infrared scanner. Walls also have much more square footage to insulate than the attic. With 4,000 square feet of walls in an average house, the cost may be $3,500 -$4,500. You won\'t break even on your investment for 15-20 years. A better option is to address the air infiltration and air loss.



Information provided by Michael Del Greco, New Jersey Home Inspector Lic. GI 0121, American Society of Home Inspectors Member 102273, Pesident of Accurate Inspections, Inc. A West Paterson New Jersey Home Inspection firm.