Deep Energy Retrofit With Exterior Rock Wool

   by Mark Yanowitz, Verdeco Designs, LLC

Throughout my 28 plus years of designing and building structures in different regions of the United States, I have been blessed with many excellent clients. In many cases, the goals and needs of my clients set me on a path of discovery, a path where I was forced to challenge my preconceived notions and embrace the concept that I am never too old to learn new things about my trade.

Sometimes the path leads me to new materials and new methods of construction and sometimes the path leads me to using “old” materials in “new” ways. It is through these clients and these projects that I find my greatest inspirations in work and reaffirm that I chose the right profession! Such was the case when I recently worked with Chris Gleba on his deep energy retrofit project over the past year.

When I first met Chris in December 2011 he explained that he had been essentially remodeling his modest two-bedroom house in Lowell,  Mass.for over ten years!   He had painstakingly rewired and re-plumbed the house, made certain energy efficiency improvements such as installed a high efficiency natural gas boiler and radiant in-floor heating, and he had devoted much sweat equity towards upgrading the interior finishes of the kitchen and baths.  Chris  explained that he had always envisioned completing the project as a high performance, low energy home, yet understood that he made some early decisions in his remodeling efforts that limited his options moving forward.

Chris had held off replacing the exterior wall finishes of his house as he hoped to build a 2nd floor addition on an existing one-story section of the house and he knew that once he did that addition it would be the ideal time to improve his overall building envelope.  As he wondered when he might be in the financial position to move forward on these exterior projects, along came National Grid’s Deep Energy Retrofit (DER) Pilot Program.

Chris  contacted my company, Verdeco Designs, LLC as we had been pre-qualified within the DER program as designers and builders with proven experience on high performance projects.  I have been progressively hearing about the use of rock wool on energy projects in recent years and, in my initial conversation with Chris, I was happy to hear of his interest in working with the product.

National Grid had established a DER pilot program to aggressively provide incentives to lower the energy demand of single floor addition on an existing one-story section of the house and and multi-family residences. Although the primary objective was to improve energy performance the program complemented financial incentives with integrated design technical support to also improve indoor air quality, durability, and overall occupant comfort. Armed with an educated National Grid program staff, the program was strengthened with the experience of Building Science Corporation (BSC), who served as program consultants, evaluating designs, and protecting applicants from themselves! It was a perfect match for Chris’s project goals as there was up to $42,000 of incentives available to meet the aggressive program goals, including rigorous air sealing goals, R40 above grade walls, R5 windows and doors, and R60 roofs. Enticed by the available funds, Chris moved towards an “all in” position on his exterior improvements.

Along with being vapor permeable, rock wool has excellent fire retardant qualities, and with being moisture and mildew resistant, it is an excellent candidate for wrapping the exterior of a building shell, perhaps as an integrated component of a rain screen design.    With all of these positive qualities, we felt committed to using it for this project.

In the end, the project was complete in December 2012 and was a smashing success! With the assistance of National Grid’s dedicated staff and BSC’s careful guidance, we comfortably achieved our air sealing goals and obtained close to the maximum incentive available.  As with the proper planning of all deep energy retrofits, this comprehensive renovation also included integrated design solutions for water management, energy systems, and controlled ventilation.  While designing low energy buildings one cannot overstress the importance of rigorous air sealing, but this project story was noteworthy largely for its selection of building enclosure components and the recognition that exterior rock wool and vapor-out assemblies may deserve a closer look as we attempt to build more responsibly.  As the debate continues on the environmental impact of manufacturing and spraying foam insulation, there is an attraction to letting buildings “breathe” rather than wrapping them in foam.