The tight house

In response to rising energy costs, a growing number of homeowners are turning to retrofit solutions to increase the performance, comfort and energy efficiency of their homes. As a result, remodeling professionals are seeing a spike in requests to help create tight, energy-efficient homes.

Although great for business, these requests can present an incredibly challenging situation for remodelers. It often means working without having the benefit of knowing what building materials and applications were used in the original structure, or if control elements on an existing building envelope are functioning at their present state, or if they were properly installed.

To help remove some of the educated guesswork, remodelers can leverage building science advancements as tools to help make air sealing, moisture management and overall energy efficiency easy and straightforward to achieve in retrofit applications.

Air sealing

Air infiltration has a direct correlation to a home’s comfort, durability and energy efficiency. Air leakage accounts for between 25 to 40 percent of the energy used for heating and cooling in a typical residence, according to “Building Envelope Improvement: Air Sealing” by the U.S. Environmental Protection Agency, especially in colder climate zones. Across all climate zones, air intrusion is one of the most significant sources of moisture that can cause condensation and damage inside the walls of a home. Remodelers have the unique opportunity to address these issues by retrofitting from the inside to add air tightness to the structure and ultimately improve the energy efficiency and performance of the home. Yet, with the average home containing nearly a mile of joints, it can be very challenging to identify the most effective areas in the home to address air leakage and infiltration issues.

To explore the complexity of air leakage, the Owens Corning Building Science Team conducted an extensive air infiltration research study that identified the specific exterior joints in a home where air is most likely to enter and escape through vulnerable gaps, cracks and seams. The study revealed that the five most important areas for builders to focus their air-sealing efforts and dollars are the top plate-to-attic, recessed lights, duct boots, band/rim joists and the garage-to-house common wall.

For remodelers, this research reinforces the importance of properly insulating the attic in existing homes. Removing the existing insulation from the attic ceiling, then properly creating an air tightness plane at the ceiling followed by adding extra, new fiberglas insulation will enhance the thermal performance, improve air tightness and maximize the durability of the structure by reducing thermal bridging and preventing moisture accumulation. The end result for homeowners is improved energy efficiency resulting in increased energy cost savings and comfort.

Moisture management

Another key metric for overall building performance is preventing moisture infiltration. Moisture acts as a pollutant inside the home and can enter the structure from built-in stored moisture, vapor transport via diffusion and bulk water from absorption of driving rains.

Rooted in the laws of physics, moisture management addresses air leakage, water movement, vapor diffusion and moisture accumulation to avoid the degradation of the thermal envelope and other potentially negative consequences. Controlling liquid and vapor moisture flow helps prevent the growth of unhealthy mold, the onset of corrosion, salt efflorescence and overall building failures.

An extreme example of when moisture management goes wrong was illustrated in 1996 when more than 3,000 executive homes in the Wilmington, N.C., area had failures handling incidental water penetration that passed through exterior cladding causing toxic mold, materials deterioration and building failure.

To avoid moisture-related failures, a good mantra to keep in mind is: insulate right, ventilate right and use the necessary control elements. It is recommended that control elements, including exterior cladding, weather-resistant barrier, fiberglass insulation and vapor control layers become fine-tuned for optimum performance.

Every hour of the day, heat and moisture is released into the home from its occupants, animals and even plants, causing vapor diffusion back and forth throughout the structure. As a result, it is critical to have continuous ventilation that achieves balance by diluting the pollutants inside and controlling humidity. New ventilation systems should be designed with fiberglass ducts to bring in fresh air from outside rather than simply relying on leakage paths that previously provided natural ventilation.

For tightly sealed, well-insulated homes, vapor control is important as the insulation and air sealing working to keep water vapor out of the concealed wall space for cold climate zones. The reverse is true for hot climates. Water vapor, or evaporated water in a gaseous state, can cause enhanced vapor diffusion when there is air movement convected through building materials.

To achieve a properly balanced residential building that handles interior loads and delivers the optimal thermal environment, building scientists are finding it is best to have a water vapor open home with dedicated air exchange. Consequently, Kraft-faced asphalt batts are smart vapor retarder solutions that open and close based on indoor relative humidity.

No need to cry WUFI

Fortunately, Ph.D.-level mastery in physics is not required for building professionals to accurately account for heat and moisture transfer impact on a building’s overall performance. Based on the newest findings regarding vapor diffusion and liquid transport in building materials, a sophisticated PC-software program can do the work for you.

WUFI (Wrme und Feuchte instationr) Fraunhofer IBP’s is a family of hygrothermal analysis tools that can be used to help predict and prevent moisture problems by normalizing variables including climate, material properties, construction and boundary conditions. Available for free download, WUFI can help building professionals create climate-specific strategies for moisture management and accurately account for correct interior loads of occupant heat and moisture in the building.

With the new research data, online programs and building science advancements available, today’s residential building industry is uniquely empowered to apply building science principles that simultaneously deliver comfort, durability, safety and energy efficiency to achieve overall sustainability. QR


Achilles Karagiozis, Ph. D., is the global director of the Building Science group for Owens Corning. He is accountable for transforming Building Science into a growth engine aimed at accelerating energy efficiency improvements in the built environment. Prior to joining Owens Corning, Karagiozis worked at the prestigious Oak Ridge National Laboratory, where he was a distinguished research engineer and hygrothermal project manager. He was instrumental in the launch of a number of innovative construction material and system products, the development of design guidelines, software tools and code changes.Karagiozis received his Ph.D. from the University of Waterloo in Ontario, Canada, with work at the von Karman Institute in Fluid Dynamics in Saint-Genese Rode, Belgium. He received his M.Sc.E. and B.Sc.E. from the University of New Brunswick in New Brunswick, Canada.