Why would you want to insulate a basement? What is hidden from view is often the most essential aspect of a home renovation—this is especially true in the basement. We’ve seen a lot of New England basements. Behind the walls and ceiling are the materials–like insulation–that make this space pleasant to spend time in. When the right materials and techniques are skipped, the result is a basement your family would rather avoid.
There is a popular myth that parts of a building set below grade are well insulated by the ground around them. Not so. Even in an unfinished basement, installing insulation for energy efficiency is essential. In a finished basement, you get the added benefit of having a pleasant, comfortable space no matter the weather outside.
Insulation Minimizes Heat Loss
One reason to properly insulate your basement is to minimize heat loss. Heat loss through uninsulated basement walls can account for up to one-third of the heat loss in an average home, which surprises many homeowners.
What can be done to better insulate against heat loss? Much of the problem is due to improper insulation around the rim joists. Rim joists are part of the framing at the perimeter of the basement that supports the outer walls above. The image to the right is an example of using foam insulation around the rim joists.
As you can see from the diagram in this document from energy.gov, when it is cold outside, cold air will penetrate the home through points of entry where mechanical and electric components like plumbing and electricity come in at the rim joist. The cold air pushes warmer air up through the home. This act of physics is often called the stack effect or chimney effect.
The best way to avoid heat loss is to seal off cold air along the rim joists, and the best way to do that is with spray foam. Spray foam seals the gaps to prevent cold air from entering the basement and has excellent insulation value. Fiberglass has good insulation properties but also acts as a filter and does not prevent air from coming in.
All those points of penetration for electrical and plumbing are also pathways for rodents and pests. Pests love fiberglass insulation. Spray foam, with its air-sealing capabilities, acts as a deterrent to rodents. The material is very unpleasant to chew, so rodents and other pests stay away.
For all of these reasons, insulating the rim joists in a basement that is not being finished can benefit the structure.
Insulation and Basement Moisture
Heat loss is one thing, but what about moisture? How can insulation help mitigate water penetration through your basement's concrete walls?
When finishing a basement, framers use 2x4 or 2x6 studs. They set the studs ½ inch away from the walls. Spray foam or rigid foam board can be used in that ½ inch gap.
Then, they will use spray foam between the studs to achieve the ideal R-value. Fiberglass insulation and a rigid foam board can be used between the studs. Either method both insulates and mitigates moisture penetration from cement walls.
Insulating the Basement Ceiling
You know how you can hear what's going on upstairs when you are in the basement? That's because the basement ceiling is not insulated. The basement ceiling consists of floor joists with subflooring material, and then carpet, tile, hardwood, LVP, or other flooring material is used on the first floor. None of that material has high insulation qualities. Walking on the first floor, especially on tile, can be very cold throughout the year in New England.
A weekend DIY warrior might attach fiberglass insulation between the floor joists. That would help with insulation and, to some extent, soundproofing between floors, but it is not an ideal material for the basement ceiling. An older solution used by tradespeople is mineral wool batt. It has similar properties to fiberglass insulation but is easier to use.
Today, there is a product on the market called wood fiber batt, which has become our top choice for this application. It is very dense and offers excellent R-value and soundproofing. It also has fire-retardant properties and is insect-proof. With wood fiber batt, you get four benefits instead of just two.
Insulating Around Plumbing and Ductwork
We’ve covered insulation for plumbing and other mechanicals entering the basement, but what about the pipes running through the basement?
From an energy savings standpoint, you want to inspect all the basement pipes and ensure they are adequately insulated. All that water you are sending from the basement heater takes time to reach its destination. The water heater is working hard to warm up those pipes, and without insulation, the pipes cool back down quickly. A foam wrap around the pipes makes a big difference, even with a low R-value.
If you have a forced air HVAC system, this is a good time to check the sealing of the ductwork running through the basement. Inadequately sealed ductwork, especially if installed long ago, makes your HVAC system work harder. We use a material called duct sealing mastic, applied with a brush, to insulate and keep ductwork from being inefficient. Properly insulating your duct supplies and returns after sealing the joints and seams will keep the conditioned air temperature values intact while it flows throughout the HVAC system making the living spaces more comfortable.
Insulating Your Basement is the Best Practice
Insulation is a hidden material that makes your entire home more comfortable and enjoyable to live in. You may not often think of the insulation needs of a basement. Yet, making sure your basement is properly sealed and insulated will improve the environment throughout the home and reduce energy costs. This is important for an unfinished space, but even more so when you plan to renovate the basement for a functional, enjoyable living space.
To learn more about the basement remodeling process, please read our eBook, “The Expert Guide to Luxury Basement Remodeling for Discerning Homeowners” And if you are ready to speak about your project, please schedule a home renovation discovery session.
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