Should Outside Walls Of Basements Be Insulated With Fiberglass?

Fiberglass insulation is a popular choice for insulating basement walls due to its affordability, effectiveness, and ease of installation. However, it is not the best type of insulation for basement walls as it can hold onto moisture, leading to potential mold, mildew, and condensation issues. To ensure proper insulation, it is essential to use insulation with R-values suitable for your climate and work with the construction.

Installing fiberglass insulation in basement walls can increase energy efficiency and reduce heat loss in your home. The most common insulation materials in basements include spray foam, fiberglass, and foam board. However, using fiberglass in the basement does not provide a barrier for moisture, as fiberglass batts are air permeable, which may lead to condensation and moisture issues.

Some builders are okay with using fiberglass and other fibrous insulation in basement stud cavities, while others think it is always a bad idea. Fiberglass insulation is usually not recommended in basements due to its air-permeability, but paired with XPS foam sheet at the wall, it can be a hybrid solution.

In conclusion, fiberglass insulation is a great option for basement walls due to its excellent thermal insulation and ability to prevent mold, mildew, and condensation issues. However, it is important to ensure that the insulation is properly prepared and installed to avoid any serious risks. Polyethylene should not be used over fiberglass insulation as it does not allow the insulation to be completely exposed.

Why not insulate basement walls?

To avoid moisture problems in a basement, it is essential to eliminate moisture before adding insulation, as it can cause the walls to rot. Insulating the inside can make the foundation walls colder, leading to condensation and long-term mold exposure. Interior finishes can also hide moisture problems, making it difficult to fix them. Obstacles like electrical panels, wiring, plumbing, stairs, and partition walls can make the insulation and air barrier less effective. If part of the basement wall is already finished, wall paneling may be difficult to remove and re-install.

Technical concerns have been raised about frost action and structural damage when foundations are insulated from the inside, as frost may penetrate deeper down the outside of the foundation wall. However, research has found that this is not a problem. In extreme climates, construction techniques may cause problems. Consult local building authorities or neighbors to ensure proper insulation and insulation.

Do I need vapor barrier on exterior basement walls?

A vapor barrier is typically required in basements with masonry or concrete framing or wood frames that touch the outside walls. These barriers, typically 4 mils plastic sheeting, allow inward drying to the basement space, allowing moisture to be removed through ventilation or dehumidification. Moisture barriers, on the other hand, go against the basement wall and behind insulation and framing. Common types of moisture barriers include waterproof paints and sealants.

Waterproof paints form a barrier that water cannot penetrate, while sealants fill in cracks and pores in mortar joints, preventing water from seeping through. Both types of barriers are essential for maintaining a dry and comfortable basement environment.

What R-value is recommended for basement walls?

The Model Energy Code recommends R-11 insulation values for basement walls in most of the country and R-15 for the northernmost states. To start insulation, construct stud walls by installing 2×2 wood boards every 16″ along the basement walls and pressure-treated 2×4 boards for the bottom plates on the floor. Trim a couple of inches from the bottom of the vertical boards to fit on top of the bottom plate. If you have windows in your basement, frame around them using 2×2 boards.

Attach the bottom plate to the floor using liquid nails adhesive, drill holes every 16″ into the floor, and drive concrete screws into the holes. Attach the vertical 2×2 boards to the wall, starting from the top and driving in screws every 2″. Ensure the boards are level and perfectly vertical before attaching them to the wall with concrete screws.

Why not to insulate basement walls?

To avoid moisture problems in a basement, it is essential to eliminate moisture before adding insulation, as it can cause the walls to rot. Insulating the inside can make the foundation walls colder, leading to condensation and long-term mold exposure. Interior finishes can also hide moisture problems, making it difficult to fix them. Obstacles like electrical panels, wiring, plumbing, stairs, and partition walls can make the insulation and air barrier less effective. If part of the basement wall is already finished, wall paneling may be difficult to remove and re-install.

Technical concerns have been raised about frost action and structural damage when foundations are insulated from the inside, as frost may penetrate deeper down the outside of the foundation wall. However, research has found that this is not a problem. In extreme climates, construction techniques may cause problems. Consult local building authorities or neighbors to ensure proper insulation and insulation.

When should you not use a vapor barrier?

In the majority of other climate zones, the use of an interior plastic sheet is not necessary, nor is the application of one on the interior.

Should basement walls be faced or unfaced insulation?

Basement walls have a higher vapor transmission probability than other building components, making facings ideal for insulation. The vapor retarder facing should face the living space, not the wall. Faced fiberglass batts or blankets can be used for wall insulation, but blankets are recommended as they are larger and have fewer seams and areas for vapor infiltration. While both types of fiberglass insulation have condensation risks, blanket insulation has less significant risks. Other insulations have better performance and avoid condensation risks, but blankets are the better choice for basement walls.

Do you insulate exterior concrete walls?

Applying continuous insulation to the outside face of a wall reduces thermal bridging and improves energy efficiency by preventing heat loss. This configuration also prevents condensation, keeping the concrete foundation wall at the same temperature as the interior air. However, there are two disadvantages to this configuration: the above-grade portion of the insulation requires protection, extending at least 6 inches, and the potential for insect infestation.

Insects may find their way through gaps between insulation panels if not properly taped and sealed. To avoid these issues, it is essential to properly tape and seal the joints to prevent insect infestation. Overall, installing insulation on the outside face of a foundation wall can offer several benefits.

What is the proper way to insulate basement walls?

This guide provides a step-by-step guide on installing basement insulation. It involves choosing 2-foot-wide by 8-foot-high, 2-inch thick polystyrene insulation panels with tongue-and-groove joints, applying foam board adhesive to the rear, and pressing the panels against the wall. The process takes about 2 to 4 hours. Insulating your basement can lower energy bills, provide more comfort, regulate temperature, and address moisture concerns. This Old House expert, Tom Silva, will guide you through the process.

Why is there no vapor barrier in the basement?

A vapor barrier is not necessary for basement walls insulated from the outside, as it can trap moisture in moisture-vulnerable areas. However, moisture tends to condense on concrete walls, causing wobble and requiring damp barriers made from moisture-resistant material. Polyurethane sheeting is the most common form of waterproofing used to prevent moisture from entering homes through basement walls.

Vapor barriers are located on the warm side of the wall in front of insulation and behind the drywall. The purpose of the waterproofing layer is to remove moisture from the walls to protect the insulation.

There are three types of waterproofing for insulation in basements: drainage, waterproofing, and vapor barriers. These layers have historically been laid outside the perimeter of basement walls, overlying rubble layers, and under concrete slabs to prevent liquids, steam, and capillary water from entering the structure. The goal is to keep the space dry and prevent mold growth and other issues.

Do exterior basement walls need to be insulated?

Insulating the exterior foundation saves energy, protects basement walls from damage, and provides a drainage plane for water. Our solutions deliver continuous insulation around the foundation, protecting homes from moisture intrusion, air infiltration, and energy loss. We offer cost-effective concrete slabs as alternatives to below-grade foundations, creating a thermal barrier for long-term energy efficiency and structural durability.

What is the best insulation for basement exterior walls?

Polyiso is a superior basement wall insulation material due to its versatility, higher R-value per inch, and versatile facers, which make it suitable for both exterior and interior applications.