Whether or not your basement is a living area, it’s important to make sure it’s properly sealed and insulated. This helps prevent outside air from getting in and cooling your home during the winter. A no-cost home energy assessment can show you how to boost your home’s overall energy efficiency, including the basement. Energy experts can offer energy-saving products for you to install, suggest upgrades, and even arrange for sealing and insulation services by weatherization professionals if necessary. 

A Mass Save® home energy assessment doesn’t typically include a blower door test. For a cost of $300 to $600, a blower door test will in most cases uncover more ways to improve your home’s weatherization. 

Air sealing

To keep indoor warmth from escaping and cold outdoor air from getting in, it’s essential to close up gaps through air-sealing. In leaky buildings, up to 40% of heating and cooling costs can be due to air leaks. The process of air sealing often involves re-sealing windows, replacing damaged vents, and refreshing the rubber seals around door frames. 

Some areas that a home energy professional will focus on for improvement: 

  • If your basement is unfinished, it’s a good idea to seal and insulate the rim joists (the area between the top of the foundation and the floor above). 
  • Electrical and plumbing openings can be sealed with foam or caulk.  
  • For basements with bulkheads or walk-out doors, adding weather stripping can help prevent air leaks.  
  • Basement windows can be sealed around their perimeter. If your windows are single-pane, upgrading them to at least double-pane is worth doing. 


Insulation slows down heat transfer through your home’s walls, roof, and floors—making it a vital aspect of winter heat retention. Collaborating with a professional contractor to enhance floor and wall insulation can significantly reduce heat transfer, enhancing your home’s efficiency. Many insulation experts prefer to air-seal before insulating, because insulation can block access to places that need to be air-sealed.  

For unheated basements or those not used as living spaces, consider isolating them from the rest of the home either by insulating between the floor joists or adding spray foam insulation to the interior walls of the basement. Talk with your home energy assessor to determine the best approach for your situation. Keep in mind that Mass Save® incentives might not cover insulating floor joists or basement walls. 

Contractor sealing rim joists in basement

We're In This Together

Pledge to reduce your home's carbon footprint by replacing old systems and appliances with clean energy technologies over time.

Join the Clean Energy Transformation

Let's work together to reduce greenhouse gas emissions from our homes and build a clean energy future for Massachusetts.