I've been an insulation auditor for 15 years working with contractors that wanted to be certified installers. As a field auditor I've seen it all, the good, bad and indifferent. The industry's dirty little secret is that 70% of all insulation jobs are under insulated. The cheating by the insulation industry is rampant. The FTC has issued special rules and fines (up to $10,000 per incident) for general contractors not meeting the contract requirements. There are three reason why insulation is shorted. Operator error caused by a lack of training or equipment failures, mislabeled packaging my manufacturing and fraud (selling low bid and shorting the material to make up for it. Loose fill insulation, like fiberglass, can be fluffed up like whipping cream, giving the illlusion of adequate R-value (based on depth). But insulation depth is only an indicator of R-value if the density is adequate. Increasing your insulation from R-13 to R-19 may not improve the thermal performance of your home. Heat moves three ways:
Radiation is heat movement through space. The sun heats the earth by radiation. Houses can be impacted by radiated heat that enters through window assemblies or through the roof.
Conduction is heat movement through a solid object. Heat transfers one adjacent molecule at a time. Convection is heat movement through a liquid. Air is a liquid. Forced air HVAC systems transmit heat convectively as do convective ovens. Most of our heat loss in our buildings is convective in nature. Fiberglass blanket is not effective at stopping air movement so it is not effective at stopping heat loss. Even when installed in a wall cavity fiberglass insulation is by-passed by convective air movement in the cavity through convective loops. Convective loops form when the air inside a wall cavity begins to move because it is cooled (and drops) along the outside wall and rises (as it is warmed along the inside wall. The warm air will rise until it get to the top and cools again as it hits the top of the outside wall, and drops. Pretty soon the cold air is pulled right through the insulation, in effect by-passing it. When selecting insulation it is best to pay attention to density. Generally the denser the insulation material the more effective the insulation. Each insulation in the list below will out perform the insulation above it:
- Fiberglass blanket (or batts).
- Dense-packed fiberglass (BIBS system).
- Cellulose (wet spray).
- Cellulose (dry packed).
- Closed-cell, spray foam.
- Open-cell, spray foam.
By Mike Holcomb