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Monday, August 27, 2007

Insulation 101 by Mike Holcomb

This is an article by a friend of mine that I thought you all would be interested in. Mike Holcomb the author of this article owns the Home Insepector General. Mike is also the director of the Alliance for Environmental Sustainability (AES) which has been selected to participate in the LEED for Homes pilot program as a provider for the Midwest.

Insulation 101

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:

  1. Radiation.

  2. Conduction.

  3. Convection.


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.
I prefer open-cell to closed-cell because hard foams can separate from the wood framing if the framing moves at all (wind loads, snow loads, humidity changes, etc.) Most insulation materials have an R-value of about 1 per inch. Would you rather have 1-inch of fiberglass (your furnace filter) or 1-inch of Styrofoam protecting you from the cold? Since most of the heat loss in a building is convective through the ceiling you should consider installing a material that can seal the attic against air movement. If you can't afford open-cell foam you should consider air sealing the attic before installing cellulose. Fiberglass should not be used in an attic with high temperature differences between indoors and outdoors. In no case should you upgrade your thermal envelop without investing in an energy audit by a qualified energy auditor. You can locate a rater in your location by going to http://www.natresnet.org/. Experienced raters can inspect your house to determine what system(s) in the house are wasting energy. Chances are that you will not be able to address all the problems but can cherry pick recommendations based on investment and benefit. I recently removed R-60 cellulose insulation from my attic and replaced it with R-24, soy-based, spray-foam. I reduced energy usage by 50%. The cost, $4,300 was recovered in 3 years.

By Mike Holcomb