Insulation
Why is Insulation Important?
Residential energy consumption is responsible for a fifth of our county’s overall carbon emissions. Most of this energy goes towards space heating, especially in cold regions like upstate New York. When a home has poor insulating properties, heat is lost via conduction, which is when heat moves from a warmer object to a cooler object that it is touching.
Insulating the PowerHouse with spray foam (photo: Mark Pierce)
Insulation minimizes this transfer of heat through conduction by using materials through which heat has a hard time traveling. The less heat that is lost to conduction, the less energy you will need to heat your home, which reduces your utility bill. If your house is heated by fossil fuels, this will also reduce your carbon footprint because less fossil fuels will need to be burned, reducing the amount of carbon emissions that result from heating your home. Reducing the energy needed to heat your house is a key step in becoming a net zero home.
What Materials Should I Use to Insulate My Home?
There is a large variety of materials that are used as insulation. Each of these options have different properties, and some are better insulators than others, meaning that they resist the transfer of heat through conduction between two objects. Most insulating materials are measured by their thermal resistance, which is their ability to prevent heat transfer through conduction. Thermal resistance is referred to as the R-value, a numeric value. A higher R-value means the material is a better insulator.
In addition to R-value, there are other considerations when choosing insulating material. Getting an audit is a great, free way to get an expert’s opinion on how to insulate your home. Visit the Get Your GreenBack website for a list of local contractors that you can contact for a home energy audit.
The table below compares the most common types of insulation:
Sources: “Comparing the Properties of Insulation Materials”, Green Building Advisor, by Martin Holladay, 7/15/2016; Prices based on internet search on 1/31/20, mostly Home Depot. Used top search results, retail prices (not wholesale). Costs do not include installation.
As can be seen, there are a variety of choices for insulation, which vary in effectiveness, with the most effective being about twice as good as the least.
For existing, older homes that are looking to fill uninsulated walls, or walls where insulation has settled, cellulose insulation, made of a fire retardant and recycled paper waste, is often an excellent choice. Its sustainable composition and good insulating ability make cellulose one of the best options for residential use. Installers can drill a series of small holes on the inside or outside of the home, and blow in cellulose, and then seal up the holes. The material also acts as a sound barrier and has a high density which prevents the travel of noise through walls and ceilings.
The XPS Foam Board used to insulate the PowerHouse floor was recycled from a local building project.
One concern about some of the most effective insulators—closed cell spray foam and XPS foam board—is the blowing agents they are made with. The blowing agents are an essential ingredient in these foam products, which make the small air bubbles in the foam that trap the heat. Until recently, the most commonly used blowing agent was a hydrofluorocarbon which was over 1,000 times more potent at trapping heat than carbon dioxide. This is referred to as the Global Warming Potential (GWP) of a material. Other, newer, blowing agents, such as those that use hydrofluoroolefin, have a GWP of 1! We clearly recommend using these latter blowing agents; however, even if you have used higher GWP agents in your spray foam the benefits may still well exceed the costs. As far as we know, the blowing agents for XPS foam board have not seen a similar improvement. So if you do decide to use this type of foam board, see if you can find it used—on Craigslist not at Home Depot!
While fiberglass insulation, a method introduced in the 1930s, is very commonly used as it is relatively inexpensive and easy to install, building science professionals generally discourage its use. It is very difficult to install correctly. Any gaps in the installation, or compressions of the material will cause it to lose its effectiveness.
How Much Insulation Do You need?
For new homes, the 2020 New York State Residential building code requires, in general terms, a minimum of R-20 for most exterior walls (and R-10 for basement walls), R-49 (or R-60) for ceilings that are part of the thermal envelope, and R-30 for floors which separate an unheated space from a heated space. These are the same for all three climate zones found in New York State, and the same requirements for an Energy Star® rated home for our region. We encourage everyone to move towards these standards, and we include them for convenience in the table below:
Installing foam board insulation on an existing home when replacing the siding. Taping the insulation seams provides an air barrier as well. (Photo: Karim Beers)
Most homes in the region were built over fifty years ago. Many lack insulation entirely, in which case blowing in insulation (usually cellulose) is a great, cost-effective solution that will have an immediate impact on your comfort and energy bills. Many other homes were built with 2x4 stud walls and have some insulation in them. In this case, one recommended solution is to install an extra layer of insulation on the outside of the home—often some type of foam board. A great time to do this is when the siding needs replacing.
Where In My Home Should I Insulate?
The boundary between the heated inside of a home and the outside is called the building envelope or building thermal enclosure. Insulating this space slows the heat flow out of your home in the winter and into it in the summer. Preventing these energy exchanges helps maintain the desired interior temperature, leading to less strain on heating and cooling systems. In the diagram below, the building envelope is represented by the orange line:
Installing insulation: start with an Energy Audit
If your think your home needs insulating, or you are not sure, you can start with a professional energy audit, which are available for free for New York residents. A professional will be able to pinpoint specific areas in your home that need insulation and suggest comprehensive solutions following the energy audit. A list of local contractors who conduct energy audits can be found on the Get Your GreenBack website, and an Energy Navigator can help you learn about and apply for programs to help cover the cost of the improvements.
Further Reading
“Next Generation Spray Foam Trickles into the Market”, Green Building Advisor, by Scott Gibson, 2/9/2017
“Avoiding the Global Warming Impact of Insulation”, Green Building Advisor, Alex Wilson, 6/1/2010, and same article with more images on the Building Green blog, 6/1/2010.
“Roofing and Siding Jobs are Energy-Retrofit Opportunities”, Green Building Advisor, by Martin Holladay, 12/4/2009 (need paid account to view full article)