Last Updated: Feb 10, 2021
When building a new house, an investment in high-performance walls can significantly cut utility costs and create a more attractive interior environment. Well insulated walls reduce energy consumption and moisture intrusion. They block exterior noise. They offer improved thermal and vapor control over traditional walls. They may even reduce the size of the heating and cooling equipment required for a home.
Some typical questions arise in building high-performance home walls. A healthy debate exists over the best methods to achieve the highest R-ratings. Homeowners have a range of options if they want to earn a certification for their house or, at least, follow guidance from LEED for residential construction or Passive House.
It would help if you also consider your climate. Guides are available for each country's climate zones, with great information on what kind of insulation works best in whatever weather you experience. Here's a primer on what to consider when having walls constructed for a new home. We've added some advice on adding thermal comfort to existing structures.
Start by working closely with your architect and contractor. The more energy-efficient the walls, the higher the price for the project. Contractors can explain the different strategies and materials and offer a report with other options. The same is true of a renovation – start by hiring a green contractor who embraces new technologies, strategies, and products.
hen researching wall construiction, you may want to look at something beyond your city's building code unless you know that you have a sophisticated code - a few cities do. Following the most recent International Energy Conservation Code (IECC) and LEED residential codes will offer you ideas on state-of-the-art walls.
Insulation is a barrier to heat flow. Heat moves through materials, like when you reach for a hot door handle warmed by the sun. Heat convection means hot air circulates through liquids and gases – warm air rises, and cooler air sinks. Radiant heat heats anything substantial in its path. Insulation slows convective and conductive heat.
An R-Value is a measurement that represents the ability of a specific type of insulation to resist heat flow. The higher the number, the better the insulation. High R-Values for walls in most of the country should be R-38, with northern climates at R-48.
We will discuss various types of high-performance insulation below, including SIPs and structured forms. There is a wide variety of other insulation types, the most common being blanket insulation that comes in batts or rolls. Blanket insulation can be made of fiberglass, plastic, mineral wool (from rock and slag), sheep's wool, or other natural fibers like cotton.
Several approaches exist. Expanding foam uses small amounts that expanding to fill space. It requires a professional. Loose-fill insulation gets blown in from holes drilled on the outside or inside of homes. Typically, insulation flows through 1"-2.5" diameter holes. Blown-in insulation comes as fiberglass treated or untreated with formaldehyde; cellulose, composed of about 80 percent ground-up newsprint and 20 percent the fire retardant borate and expensive mineral wool.
Generally, high performing walls have four layers to deal with moisture resistance, air control, vapor resistance, and thermal comfort as follows:
Let's talk about each of them.
The US Department of Energy suggests placing a water control layer either in front of or behind insulation, but not in-between. By having the barrier on the outside water has little chance of getting inside.
Experts say air control layers separate conditioned (or inside air) with the outside environment. A sheet that stops air transfer can be placed either on the exterior or interior. Sheathing on the outside and gypsum board on the inside is one common approach.
Putting an insulating layer on the outside of the sheathing, especially in cold climates, reduces the vapor problem. When the exterior warms, water does not condense and enter the walls, removing the need for an interior vapor control layer.
High-performance insulation may add as much as 4 inches to the home's exterior. Though more than standard, it is not enough to be noticeable.
External home insulation allows a more continuous and more complete coverage of the framing. The approach provides minimal thermal bridging that causes unwanted heat loss or gain.
Frame walls have a cavity that can be insulated. Adding insulation insides creates an even better thermal seal. Look for insulation that helps you attain your sustainability goals - be it that they come from nearby sources, are renewable, or are made with natural fibers.
Structural insulated panels (SIPs) combine all the layers and remove the need for wood framing. Manufacturers sandwich insulated foam core between two structural facings composed of oriented strand board. Advocates say the result is a robust and energy-efficient home that may cost about the same as a traditional house when considering saving on construction time and creating less waste. Insulated concrete forms (ICF) and blocks can be installed, but their R-values may not be as high as homes made with SIPs.
ZIP Systems R-Sheathing offers air, water, and thermal management through sheathing nailed into studs and then taped to form a strong seal. The product consists of an oriented strand board (OSB) with a vapor mesh over it painted green. It keeps out air and water in one layer. Dupont's Tyvek is another popular option that offers a product with layers built in that may work.
The website Earth911 suggests that fiberglass insulation requires a lot of energy during its production, and some products still contain formaldehyde. Fiberglass often includes 20 percent of recycled materials. Look for products certified by GreenGuard, such as Ecobatt and Sustainable Insulation by Certainteed. Mineral wool production has been linked with air quality issues in the surrounding areas. Both fiberglass and mineral wool insulation, however, work better in humid climates than their more environmentally friendly counterparts. Homeowners considering polyurethane foam insulation and rigid foam insulation with fire retardants should research any issues related to off-gassing and global warming potential (GWP) factors.
This topic is definitely up for interpretation, depending on what factors you take into account. However, great all-around contenders include cellulose insulation (composed of recycled paper and other benign materials) and cotton batt insulation (made primarily from recycled denim). However, it should be noted that neither of these performs as well in areas where with high moisture levels.
Based in St. Paul, Frank Jossi is a journalist, editor and content strategist. He covers clean energy in Minnesota for Midwest Energy News and writes frequently for Finance & Commerce. His work has appeared in more than 70 local, national and international publications.