In Perspective - Insulation
I thought today's column should cover insulation. Heating and cooling account for 50 to 70% of the energy used in the average American home. Poor insulation and air leakage are major causes of energy waste in most homes.
There are many types and applications for insulation. Most of us are familiar with the fiberglass batt insulation. But is the fiberglass batt insulation the best for all projects? Let's first cover what insulation does.
Heat travels from warmer too cold any time there is a difference in temperature. Heat also rises while cold air sinks, both movements are important when dealing with insulation. In winter, heat usually moves from indoor to outdoors. It moves in three different ways referred to as conduction, convection and radiation. Conduction is heat transfer through matter. Put a pot on an electric burner and it is warming by conduction, one thing touching another. Convection, on the other hand, is heat transfer by the movement of mass from one place to another and takes place only in liquids and gases. Radiation is the only way heat is transferred that can move through the relative emptiness of space. Insulation is used to slow the transfer of heat. Insulation is rated in terms of thermal resistance, called R-value. The higher the R-value the greater resistance to heat transfer. All insulation is measured by the thickness so you will see things like batt insulation with a thickness of 6 1/4 inches with a R-value of 19. So it has a R-value of 3.04 per inch. But there is a catch, there are wood studs in the wall and the R-value for wood is around 1.40 per inch. So a 2x4 wood stud has a R-value of about 4.9. So every 16 inches about 15 inches is R-value 19 and the other inch is R-value of about 5.
There are also different types of insulation besides the fiberglass batt. There are three types of loose-fill insulation, fiberglass, rock wool, cellulose which has a R-value range of 2.3 to 3.7 an inch which is close to fiberglass batt. Then there is the expanded polystyrene board with a R-value of 3.6 to 4 per inch. Extruded polystyrene board has a R-value of around 4.5 to 5 per inch. Polyisocyanurate board has a R-value range of 5.6 to 7 and then there is Spray polyurethane foam that has a R-value range of 5.6 to 7 per inch.
The boards are commonly used on the exterior of a wall before cladding such as brick or aluminum siding is installed. It can also be used in the cavities of walls. But you usually don't see it on attic floors very often. What you do see in attics is the loose-fill cellulose. It is inexpensive and easy to install if you have easy access to the attic. Spray foam is used in new buildings and retrofits. Studies in Florida have shown that spray foam can strengthen roofs and walls making them more resistant to high winds. Another advantage of spray foam is that it resists moisture, water and mold much better than fiberglass or loose-fill. It also stops air flow through walls which is a real disadvantage of fiberglass.
One more thing to keep in mind and that is the recommended R-values for our local zone. The attic should have a R-value of R-49, walls a R-value of 16 and floors over unconditioned space should be R-value of 25. Even basement walls should have R-value of 11 to 13.
A couple of weeks ago I mentioned that LED residential lights were about to hit the market. We should see these light bulbs next year.
Philips has developed, manufactured and will bring to market a LED replacement for the common 60W incandescent light bulb.
* Efficacy of more than 90 lumens/W, which exceeds the efficiency of all incandescent and most compact fluorescent sources today
* Energy consumption of less than 10 watts as compared to a 60-Watt incandescent.
* Output of more than 900 lumen, equivalent to a 60-Watt incandescent light bulb
* Lifetime of more than 25,000 hours, which is 25X greater than a typical incandescent bulb
* Color Rendering Index (CRI) greater than 90, which is a high measure of lighting quality
* Color Temperature between 2700-3000K, (“warm” white light)