Adding home insulation is one of the most cost-effective ways to save money on energy bills in an older home. A well-insulated basement reduces heat loss to the surrounding ground and makes your entire home more comfortable.
Insulate Basement Walls or Ceiling
In homes with unfinished basements, it may make sense to insulate the basement ceiling, but usually it is better to insulate the walls instead. First, it will require fewer square feet of insulation. Second, it is usually easier to create a continuous air barrier long the walls than along the ceiling because basement ceilings usually have a lot of pipes, ducts and wires along them. Third, insulating the walls instead of the ceiling will increase the comfort of your basement without affecting the size requirements of your heating system. This is because the heat loss would be approximately the same through the ceiling or walls.
Interior or Exterior
Basement walls can have insulation added to the interior or exterior of the walls. Generally, for existing homes it is easier and less expensive to install insulation on the interior of basement walls. Unless you are already doing foundation work, like installing a perimeter drain, excavating to add insulation is probably not worth it. Exterior insulation is much more practical for new homes than existing homes.
Types of Basement Wall Insulation
The type of insulation you use will depend on how much insulation you need, moisture control considerations, and whether your basement is finished or unfinished. In general, batt or rolled insulation is the most common and least expensive type of insulation for interior basement walls. Foam board is also common for interior basement walls and typically has a higher r-value per inch. It also works on the exterior of a foundation wall, but is susceptible to insect tunneling. When installed internally, fire protection such as a layer of gyp-board is usually a requirement, so check your local code or higher a qualified professional to do the installation. For finished basements, loose fill or sprayed foam insulations are convenient for getting into existing finished walls.
How Much Insulation
The amount of insulation you should add to your basement walls depends on the climate you live in and the amount of insulation your home already has. In most locations in the US, basement walls should have enough insulation top provide an r-value of 5 to 19, depending on climate zone. The farther north you live, the more insulation your basement should have. Insulations have ratings of r-value per inch. Determine how much additional insulation you need based on your climate and existing insulation and select an appropriate insulation type and thickness to achieve that level.
Hire a Professional or Insulate Yourself
You may wish to install additional insulation yourself to save money. If you know what you are doing, go for it, but if you are uncertain, please hire a professional. The performance of insulation depends on its installation. Gaps and air leaks drastically reduce its effectiveness. Other considerations such as moisture barriers and radiation mitigation may also need addressing by a professional. Moisture barriers are particularly important in basements because of the tendency of these areas to get damp and moldy. If the surrounding soil contains radon, adding insulation and air barriers may trap radon gas. A local installer will be aware of local codes and soil conditions.