Thermal Insulation 101

There are 3 main ways that heat energy is transferred from one substance to another – convection, conduction and radiation. Thermal insulators retard these processes.

R-Value: A construction industry measure of a materials ability to resist thermal energy transfer.

Space Age Insulator

Aerogel is an extreme insulator. Shown here, a thin slice of Aerogel stops wax crayons melting even though the blowtorch is pointing directly at it. Called a gel because of the way it is manufactured it presents itself as a light almost transparent solid with extremely high melting points, incredible R-values and ultra-low weight. It is reasonably strong. Strength, transparency and other mechanical properties are strongly affected by the manufacturing process. These insulators were used on the Mars Rover. An 18mm layer of aerogel will be sufficient to protect astronauts from temperatures as low as -130C. A sheet of Aerogel as a replacement for glass in a window provides 10-20 times the insulating power. “You could take a two- or three-bedroom house, insulate it with Aerogel and you could heat the house with a candle. But eventually the house would become too hot” – Dr Peter Tsou, Nasa JPL.

R-Values: 14 to +100

Weight : 3 times the weight of air.

Melting : 1200 °C (Silica Aerogel)

Starting to be used for skylights
AirGlass is a variant, similar to Aerogel ,used for window applications as an energy saver and as windows in firewalls.

Engineering Units - Watch Out you can easily be ripped off.

• R-Value is not unit-less.

In the USA the common units are ft², °F, h/Btu.

The metric units are m².K/W

1 R value (USA) = 0.17611 m².K/W (SI Units)

• R Values are calculated / published for a standard set of conditions such as constant temp and no air flow. Thus the published R-value and the effective R-value can be very different.

Aerogel Brand Names

These products are still expensive and some are hazardous to handle (nano particle dust).

Spaceloft = thin aerogel blanket/sheet made by Aspen Aerogels.

Common Insulators for Home and Commercial Buildings

Fiberglass batt

Completely useless at stopping air and moisture flow. Must be accompanies by air movement barrier. Installation quality sensitive.

Blown Fiberglass

Less sensitive to Installation quality. Check for cavities (how ?) Higher density means its better at stopping energy loss due to convection. Minimum wall cavity dimensions and non-self supporting limit applications.

Blown Cellulose

Similar to blown fiberglass. Densities are a little lower and R-value is lower. Made from flammable materials so must be treated.

Urethane Foam

R-value is stable in adverse weather conditions. Stable, self supporting. More expensive. Excellent at convective, conductive and radiation heat loss.

Studs – A huge waste of energy

The problem is that metal studs conduct heat many times faster than wood, serving as a sort of heat-loss superhighway. To prevent excessive heat loss, the studs must be properly insulated and sealed into the walls. The most commonly used and recommended solution is an exterior layer of rigid insulation sheathing to break that thermal bridge. But not all builders who use steel framing are addressing the alternative stud's shortcomings.