Ask an Expert: How to choose insulation with the lowest carbon impact

May 5, 2022 | 5 min read

Weatherizing your home can help you stay warm and save money. It can also lower your carbon footprint. But not all insulation materials have the same carbon impact. Brian Just is the Director of Engineering at Efficiency Vermont. He recently investigated the different carbon impacts of insulation materials. This was an Efficiency Vermont Research & Development project. We sat down with Brian to learn more.

We know that not all our readers are insulation experts, like Brian, and insulation is a complicated topic. So we’ve included a handy little glossary here to help out:

  • Research & Development (R&D): This encompasses work done (in this case at Efficiency Vermont) that doesn’t directly involve a customer-facing product. Instead, it’s innovation and testing of new products that might someday be available for customers.
  • Carbon footprint: a generic term for the amount of emissions from a certain product, process, or activity.
  • Embodied carbon: The carbon emissions from something (in this case, insulation materials) from every stage of its life: the creation, transportation, installation, and use.
  • Types of insulation (check out this guide for more detail):
    • Boardstock: insulation that comes in large sheets
    • Batts: insulation that comes in flexible pre-cut form, for putting between framing in walls and ceilings
    • Dense pack: insulation that is tightly blown in to create a dense layer inside a wall or ceiling cavity or other tight space
    • Loose fill: insulation that is blown in to create a fluffy insulating layer in a larger open space (often used in crawl spaces and attics)
Why did you want to understand the relative carbon impacts from insulation materials?

Brian: Construction material choices affect the carbon footprint of a building. We knew that was the case for insulation materials as well. But we didn’t know how big of a difference these materials could make By pulling together the available data, we could increase awareness around lower-carbon options. We work closely with partners in the supply chain – manufacturers, dealers, and contractors. By shedding light on the issue, we could help our partners and customers make choices with a lower carbon footprint.

This is why Efficiency Vermont invests in Research & Development (R&D). R&D allows us to create space for innovation that will better help Vermonters.

We can investigate next-generation technology. If we determine that technology can benefit Vermonters, we can help bring it to the market. That’s an important part of helping Vermonters continue to save energy and reduce their carbon footprint.

What's included in the carbon footprint calculation of these materials?

Brian: There are two different types of carbon impacts from insulation materials. The first is the one most people think about. Insulating our homes and businesses reduces the energy needed to heat and cool those buildings. That reduces their carbon footprint.

But all insulation materials (in fact, all building materials) also have embodied carbon. Embodied carbon accounts for the material’s emissions as it is created, moved around, installed, and used.

Which insulation materials have especially low or high carbon impacts?

Brian: Materials with the lowest embodied carbon include wood fiber and cellulose. Wood fiber comes in boardstock and batts. Cellulose comes in dense pack or loose fill.

The materials with the highest embodied carbon are closed cell spray foam and XPS (extruded polystyrene). XPS, often called pink board or blue board, is one of the most widely used insulation materials and closed cell spray foam is very common in weatherization and renovation projects. These materials can be effective at reducing both air leakage and heat loss in a building, which helps reduce carbon emissions from heating a home. But the creation process results in more emissions than most other insulation materials.

There are several materials that fall somewhere in the middle. Fiberglass, polyisocyanurate, expanded polystyrene (or EPS), open cell spray foam, phenolic foam, and cellular glass all have lower impacts than closed cell spray foam and XPS.

We created a one-pager that shares the simplified results of our analysis.

What's included in the calculation of a material's lifecycle carbon emissions?

Brian: The calculation starts with the supply of raw materials. Where did they come from? What does it take to mine, collect, or create them? Then those raw materials are transported to a factory for manufacturing. Transportation creates emissions, so the transportation distance and method impact the final calculation. Then we add in emissions from the manufacturing. How much energy is used to turn the raw materials into the final product?

Finally, we calculate emissions from the installation and use of the materials. Some materials have carbon impacts from when they are being installed. Some materials release harmful refrigerants (also known as off gassing) throughout their lifetime. Each of these sources is added into the final calculation.

Are lower-carbon insulation materials in use today?

Brian: Our project included case studies with low-carbon materials in new home construction. We provided incentives to help participants try new materials. We chose project partners who were likely to continue using these materials in future projects.

The first project was an affordable multi-family home in northern Vermont. The builder found that the alternatives cost less than $100 more than what he was planning to use. But they saved him money and time on labor and installation. This will make it more likely that he’ll use lower-carbon materials in future projects.

The second project was a single-family home in Chittenden County. The builder and architect switched to a lower-carbon material for the exterior walls. But they didn’t want to switch for the foundation walls. Supply was a challenge. The alternatives weren’t as readily available. But they were also reluctant to try something unfamiliar. This project helped pinpoint two of the biggest barriers: the supply of new materials and bringing awareness of new methods to builders and architects.  

Are there any other benefits to using lower-carbon materials?

Brian: My analysis focused on the carbon impact. The BuildingGreen Guide to Insulation includes environmental attributes and health concerns. We found that lower-carbon materials generally also had the lowest toxic emissions. That means that they may be better for the health of installers and building occupants. These materials also tended to have the most recycled materials included.

As our first case study found, low-carbon materials can also bring cost savings. Today, they’re sometimes more expensive than the higher-emitting materials at face value. But the way they’re installed, and the amount of material needed, may result in savings for the whole project. Bulk discounts can help too. If builders commit to using these materials for several projects, they become even more  cost-effective.

How can I make sure my next insulation project uses lower-carbon materials?

Brian: Whether you find a contractor or call Efficiency Vermont first, we can all work together to help you understand what might work best for your next project.   Most lower-carbon materials are not new, but they are not yet as common. And there are some new materials starting to be manufactured in the U.S. today that were previously only available from overseas. The best way to increase their supply and bring down the cost is to increase demand for them. By asking for them as part of your project, you can help increase their availability for future projects.

Insulation isn’t the only way you can reduce the carbon footprint of your next project. All building materials have some carbon footprint. Concrete, for example, is a significant contributor to a building’s carbon footprint. Using a lower-carbon concrete alternative can reduce the embodied carbon by 14-33% without increasing the price.