A Study in Siding

With energy costs on the rise and homeowners looking for ways to reduce utility bills, energy-saving projects are some of the best home-improvement options to grow an exterior contracting business. But replacing windows isn’t the only way to secure savings for strapped homeowners. Contractors who want to capitalize on the energy-efficiency trend, and who think outside the window, can help consumers save money with insulated siding while improving the comfort and curb appeal of their homes.

Insulated siding is vinyl siding with rigid foam insulation laminated or otherwise permanently attached to the panel. In codes and voluntary programs, insulated siding qualifies as continuous insulation that reduces the thermal-bridging effect, which is the transfer of energy through framing members or studs. Thermal bridging can rob a well-insulated home of conditioned air and increase energy consumption.

Installed outside of the building framing, insulated siding helps reduce energy loss through thermal bridging and air leakage, which improves the overall R-value of the wall assembly. R-value is a measure of thermal resistance; the higher the R-value, the better the insulation’s overall effectiveness. Because it has been tested to improve R-values in certain wall assemblies, insulated siding is listed in the International Energy Conservation Code among the materials that can be used as continuous insulation outside the building framing to provide the required total wall R-value in the coldest climate zones.

To demonstrate insulated vinyl siding’s energy-efficiency performance in the field, the Washington, D.C.-based Vinyl Siding Institute commissioned energy research firm Newport Ventures, Schenectady, N.Y., to determine insulated siding’s effect on existing homes under real-world conditions.

Insulated siding from four different manufacturers was installed on four existing, single-family homes in four cities located in two of the colder U.S. climate zones. The cities included Burnt Hills, N.Y.; Fort Collins, Colo.; New Palestine, Ind.; and Severna Park, Md. VSI-certified installers removed the existing siding, placed a water-resistive barrier over the existing sheathing and installed new insulated siding with R-values ranging from R-2 to R-2.7. (See the table on page 58.)

Newport Ventures conducted three blower-door tests to determine the air tightness of the homes. The first one was conducted with the existing siding, the second once the siding was removed and a water-resistive barrier was installed and the third after the new insulated siding was installed. All four homes showed air tightness increases an average of 12 percent after insulated siding was installed.

The study also simulated pre-and post-insulated siding conditions to predict the expected heating energy savings for the four homes. Computer simulations were conducted using EnergyGauge USA software, which uses the DOE 2.1E engine and is recognized as an accredited building energy rating software by the Residential Energy Services Network. These simulations projected the R-value effect of the insulated siding and the air-tightness improvement measured for each individual home. The building energy simulations showed heating energy savings from 5 to 12 percent with an average savings of 8 percent for all four homes.

Finally, Newport Ventures used the energy simulations to produce a Home Energy Rating System (HERS) index for each of the four homes. All four homes experienced a HERS index improvement between 2 and 8 points after the existing siding was replaced with a water-resistive barrier and insulated siding based on energy-simulation results.

To gauge the effect of the insulated siding on heating energy use throughout a longer period of time, the owners of the four homes agreed to supply Newport Ventures with utility bills for two years leading up to and after the insulated siding retrofit. VSI published the interim results of Newport Ventures’ “Insulated Siding Energy Performance Study” last year and the final results are expected in early 2013. To download a copy of the interim study, visit Insulatedsiding.info.

Matt Dobson is the code and regulatory director for the Vinyl Siding Institute, Washington, D.C. He is a member of the International Code Council’s Code Development Committee for the International Building Code, a consensus committee member for the development of ICC 700, National Green Building Standard, and a member of NAHB.