Want to do more with your damp, energy-draining basement? Insulation can help.
Today, people want their basement to be a comfortable and moisture-free environment, suitable for human habitation and property storage. The cheapest and most effective way to achieve a livable basement is with insulation. Insulation is designed to keep conditioned air in and the elements out.
An insulated basement is optimally energy efficient. Basement wall insulation locks in expensive conditioned air and blocks outdoor temperatures to keep your home’s energy system functioning at maximum efficiency. The basement is often a major source of energy loss in homes, says the U.S. Department of Energy.
Insulating basement walls maximizes their longevity. Without proper insulation, homeowners eventually see the buildup of moisture and ultimately hazardous mold and mildew. Effective basement insulation acts a waterproof vapor barrier. It also helps prevent pest infestations and improves air quality.
How To Insulate A Basement
You can insulate a basement wall from the inside or the outside. The latter is usually done at the time of construction. Although exterior insulation is ideal for energy efficiency purposes, interior insulation is the easiest and cost-effective option for most home improvement projects. It is most practical when the basement has been constructed but is still unfinished.
Interior basement insulation can be done by a savvy do-it-yourselfer – although some people bring in a contractor to ensure the highest quality work. If you want to be your own handyman, learn how to insulate your slabs with our best tips for DIY basement wall insulation.
Type of Insulation
The most popular basement insulation materials are packaged as batts, rigid panels, or spray foam.
- Batts are essentially rolls or blankets made from mineral fibers, such as fiberglass or wool. Fiberglass batts are a cheap insulation material, but they come with some disadvantages that are worth considering – see below.
- Rigid foam insulation is both more effective and expensive compared to batts. Rigid sheets or panels of extruded polystyrene, or XPS, are the best choice of material for many homes. One or two inches of XPS provides tough and moisture-resistant insulation. However, XPS is flammable, so it must be installed with a thermal barrier, such as a half-inch of gypsum board.
- Foam-in-place insulation, or spray foam, can be sprayed into empty cavities to fill the entire space. Spray foam insulation achieves a higher R-value with less thickness. Closed-cell spray foam is widely considered the best way to insulate a basement wall, but it is more expensive than rigid panels.
What is the best R-value for your insulation? It depends on your climate, home design, and other factors. The Department of Energy provides a handy tool for calculating appropriate R-values based on your zip code.
To achieve a higher overall R-value, many people use a combination of materials. It’s common to lay rigid foam board against the foundation, then construct a stud wall on top. The stud wall leaves space for electrical wiring and HVAC infrastructure, and can be further insulated with batts between the studs. If you plan to install additional insulative sheathing, you can use thinner foam boards for the first layer.
Did You Know? Moisture Control Tips
The main difficulty in insulating basment walls relates to moisture. Concrete walls absorb water like a sponge, easily transporting moisture inside from the outdoors. One of the benefits of insulation is its vapor resistance, but it must be installed correctly to prevent, rather than aggravate moisture issues.
If you have serious moisture infiltration, you must fix it before applying insulation so your efforts don’t go to waste. If you notice any visible wetness on the foundation under ordinary conditions, you probably need to install a drainage system first.
Basement wall insulation should be applied directly to the concrete foundation – unless you’re using fiberglass batts. If you insulate with fiberglass, there must be space between the insulation and concrete. Otherwise, the point of contact will acquire mold or mildew. This is a surprisingly commonplace mistake. Fiberglass is not moisture-resistant!
Should you include a plastic vapor barrier between your layer of insulation and the drywall? According to the Building Science Corporation, vapor barriers do more harm than good. Properly installed insulation is the best defense against moisture and avoids the air flow problems that accompany plastic barriers.
When installing fiberglass insulation, safety precautions are important. You can protect your health by wearing eye, mouth and skin protection. Use shop goggles and a dust mask. Be sure all exposed skin is covered and wear work gloves.
When you place a fiberglass batt in a wall cavity, don’t press too hard. Instead of squishing the material in, cut the insulation with a sharp knife to the desired size or shape. You can cut small pieces to fill minor spaces and achieve airtight protection. Aim for a tight, but not pinched fit.