Where To Insulate In Your Basement

Basements must have insulation. An insulated basement is a requirement to meet building codes. Basement insulation also contributes to energy efficiency and home comfort. The question is, where does insulation need to be installed in the basement?

South Central Services has insulated hundreds of new and existing homes with spray foam. Many of the homes we insulate around Mercersburg, PA have basements. The basement is a crucial area to insulate. Whether you're building a new house or upgrading your current home, basement insulation is necessary.

By the end of this article, you will understand:

• Why basements need to be insulated
• Where insulation can be installed
• If your basement needs insulation
• Which area to insulate in your basement

Why Do Basements Need Insulation?

Your basement is part of your thermal envelope, which forms the barrier between your home and the outside. Exterior walls, attics, basements, and even crawl spaces are part of a home's thermal envelope.

A basement without insulation contributes to cold floors, temperature fluctuations, and even draftiness. Not only are these things uncomfortable, but they also impact your energy costs. When you blast your AC or bump up your thermostat a few more degrees, you pay for that comfort in your energy bill.

By insulating your basement, your home's thermal envelope has an effective barrier. An effective thermal barrier can stop cold floors and energy inefficiency.

Where Should Insulation Be Installed In A Basement?

There are three areas where insulation can be installed in a basement: the band boards (or rim joists), the ceiling, and the walls.

You do not have to insulate every area of your basement. Where you insulate and what insulation product you use will depend on how you plan on using your basement.

Let's examine these places in your basement in more detail.

Basement Band Boards

The band boards, also called rim joists, of your basement are a key area where cold air infiltrates.

Your band boards are the transition from masonry walls to wood framing. Transitioning from one type of material to another makes this area vulnerable since the materials have different properties. An example is porosity. Masonry is porous, while wood is not.

The basement rim joists are also notoriously difficult to insulate. To ensure they are “technically” insulated, fiberglass batts are generally stuffed into the band boards. Fiberglass cannot stop the air infiltration and is at risk of condensation. Rigid foam boards would offer better performance, but cannot conform to the angles and crevices of a band board.

Even though band boards contribute significantly to air infiltration, they are rarely insulated effectively.

We recommend closed cell spray foam insulation for basement band boards in almost every situation. While there may be exceptions, most homes should have an airtight seal in the rim joists of the basement. Insulating this area can make the home more comfortable and energy efficient. As a bonus, it's also one of the least expensive spray foam upgrades for existing homes.

Unlike foam board, spray foam insulation can conform to any contour in the rim joists. Being spray-applied allows for a continuous and seamless application. Closed cell spray foam can also create an airtight seal with as little as 1 inch of insulation. An airtight seal stops air infiltration, which in turn stops cold floors and drafts.

Basement Ceilings

You can insulate the basement ceiling, but you don't have to. If you choose not to insulate the basement ceiling, you must insulate the basement walls. If you don't want to insulate the basement walls, you must use high-performing insulation in the ceiling.

The basement ceiling can be a tricky area to insulate. In some homes, the basement ceiling is home to plumbing, electrical, and HVAC. These protrusions can complicate insulation.

Insulating the basement ceiling essentially separates the basement from your conditioned living space. The HVAC equipment pumps warm and cool air to the rest of the home but not to the basement. Ceiling insulation can work well for an unfinished basement that you use for storage or don't use at all.

If you finish your basement, you may still want insulation in the ceiling. However, you create a soundproofing layer instead of cutting off the basement from the HVAC system.

You could use open cell spray foam, batt insulation, or soundproofing materials for your basement ceiling. Which is right for you will depend on how you want to use your basement space.

Basement Walls

Due to their surface area, basement walls are more expensive to insulate than basement ceilings. However, wall insulation is required if you plan on finishing your basement.

Insulation may not be directly applied to the masonry walls for a finished basement. Since you'll need to attach drywall to something downstairs, a wood-frame wall should be constructed in the basement. Insulation can be either stuffed into or sprayed onto the new wall, or sit in between the wood and masonry walls.

Unfinished basements can also opt for wall insulation. However, no secondary wall is required for this type of application. Instead, insulation can be spray-applied or fastened directly to the basement walls.

Which Area Of Your Basement Should Be Insulated?

If your basement band boards poorly insulated, consider hiring a qualified spray foam contractor to insulate those rim joists. While band boards may not require effective insulation to meet building codes, they contribute to problematic air infiltration.

Insulating your band boards with closed cell spray foam should lower your energy bills and make your home more comfortable.

If you want to finish your basement, you will need new wall insulation. There are different options for wall insulation, ranging from budget-friendly to high-performing.

If you don't plan on finishing your basement, you could insulate either the basement ceiling or walls. The ceiling should be more cost-effective since it is a smaller square footage.

Homes with enough basement insulation have insulated band boards, wall or ceiling insulation, and are not facing cold floors or drafts.

The Bottom Line About Where Basements Should Be Insulated

Basements need insulation. You can choose between wall and ceiling insulation to meet building codes. One of those areas must be insulated to meet building codes and complete your thermal envelope.

Whether you choose ceiling or wall insulation, your rim joists should be insulated. Basement band boards are a vitally important area where cold outside air infiltrates your home. Closed cell spray foam is one of the few options for rim joists due to their awkward shape and the qualities of masonry.

Now that you know where you can insulate in your basement, your next step is to:

• Compare insulation options for your basement ceiling
• Discover how to evaluate spray foam contractors
• Learn why others trust South Central Services to insulate their basement