On February 22, 2006, the Service issued Notice 2006-26, 2006-11 I.R.B. 622. This notice clarifies that section 4.04 of Notice 2006-26 should read as follows:

.04 Specifically and Primarily Designed. A component is not specifically and primarily designed to reduce heat loss or gain of a dwelling unit if it provides structural support or a finished surface, as in the case of drywall or siding. In addition, a component is not specifically and primarily designed to reduce heat loss or gain of a dwelling unit if its principal purpose is to serve any function unrelated to the reduction of heat loss or gain. For purposes of the preceding sentence, the principal purpose of a component serves functions unrelated to the reduction of heat loss or gain if—

(1) Production costs attributable to features other than those that reduce heat loss or gain exceed production costs attributable to features that reduce heat loss or gain; or

(2) The facts and circumstances otherwise establish that the component’s principal purpose is to serve a function other than heat loss or gain.

Taxpayers who purchased siding on or before June 26, 2006 may rely on a manufacturer’s certification that the siding is an Eligible Building Envelope Component for purposes of the section 25C credit. A manufacturer will not be subject to penalties under § 7206 or § 6701 on account of a certification that siding is an Eligible Building Envelope Component under section 4.02 of Notice 2006-26 unless the manufacturer continues to provide the certification to purchasers of the siding after June 26, 2006.