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What is a Band Joist? Explained



V Susan
Hi! I'm Susan. I am passionate about woodworking, general DIY and home improvement. If you'd like to connect with me or talk about something you like at mellowpine, drop me a mail at susan@mellowpine.com


Band Joist

A band joist or rim joist is a structural component that provides lateral support to joists, preventing deformations under the weight of load-bearing walls that rest on them. These joists are installed perpendicular to the joist’s ends and are made of solid lumber, engineered wood, or steel.

What is a Band Joist?

In residential construction, joists play a vital role in providing stability to floors and roofs.

They are typically made from lumber and have a spacing of 16 inches.

Band joists are installed perpendicular to floor and ceiling joists by nailing their ends, and they run along the perimeter of the floor framing system.

The primary function of a band joist is to provide lateral support to other joist members in a floor or ceiling to increase their strength and stability.

When building a deck using floor joists, they form the boundary and prevent joists from shifting, thereby maintaining the structural integrity of decks.

Additionally, they secure the railing posts in decks.

In a typical house plan, band joists lie on top of sill plates, which are flat plates connected at the bottom of a floor-band joist connection and secure stairs and railings.

Band joists in such situations are load-bearing.

Load Bearing Band Joists
Load Bearing Band Joists

Exterior sheathing applied to band joists acts as a nailing base and provides a protective covering.

However, if your structure is non-residential and is intended to bear heavy loads, consider a floor truss system instead of a traditional floor joist.

What are Band Joists Made From?

Like other joists, band joists are made of traditional lumber or steel, depending on the design requirements.

Alternatively, engineered wood can be used due to its strength and durability.

In some cases, the band joist is made of steel, while the inner floor joists are made of wood.

Steel Band Joists
Steel Band Joists

Size of a Band Joist

Band joists are typically of the same size as other joists and maintain alignment with them.

To increase the strength and durability of a floor frame and to reduce the bounce on it, you need to increase the area of band joists.

To do this, install double band joists across the perimeter of the joists.

Alternatively, you can also block or bridge joists to reduce floor bouncing.

However, the specific method depends on the engineering considerations.

Should You Insulate Band Joists?

Applying proper insulation to band joists significantly reduces energy costs and maintains a comfortable indoor temperature throughout the year, keeping the house warm in winter and cool in summer.

Here are the different ways to insulate band joists:

  • Insulate the interior face of a band joist above the foundation wall.
  • Install rigid foam insulation boards on exterior walls, extending down to cover the band joists.
  • Place fiberglass insulation into the band joist cavities.
Foam Insulation of Band Joist
Spray Foam Insulation of Band Joist

Fiberglass is an easy-to use insulating material that can be cut into different pieces to meet the required dimensions.

However, using fiberglass may lead to mold problems as it can let air and moisture.

To prevent mold,rigid foam is a better option.

On the other hand, spray foam provides a better covering but are more expensive than other types.

The best option is to provide insulation during the construction phase of a house.

Insulating post -construction can pose challenges as drywall can block access to the areas that need insulation.

fiberglass insulation in band joist
fiberglass insulation for band joist

Can you Drill Through a Band Joist?

It is common to drill holes into band joists to accommodate pipes, vents, and wires.

Drill carefully to not affect the strength of the joists.

Holes drilled into a band joist
Holes drilled into a band joist

Typically, holes with a diameter of 1-1/2 inches are drilled throughout the web of the band joists.

When larger holes are required, it is advisable to position them more toward the middle of the joist rather than at the ends.

Can Band Joists be Replaced?

If the band joists are severely damaged due to environmental conditions or pest infestation,it is easier to replace a section of band joists.

First,remove the sheathing and relocate the wires and pipes.

Temporary support is also necessary during the replacement process.

Next,remove the damaged section and replace it with new band joists and secure with hangers and bolts.

Afterward,reinstall the utilities and provide insulation to reduce the need for heating and cooling systems.

Frequently Asked Questions (FAQ)

How Much Does it Cost to Repair a Band Joist?

The cost of repairing band joists depends on the extent of the damage ,ease of access and labor costs of your region.

On average, the cost for repair for a single band joist lies between $100 to $200.

What is the R-value of Band Joist Insulation?

It is generally recommended to use insulation materials with a minimum R-value of R-13 to R-20 for band joists.

This can help reduce heat transfer and lower the energy costs.

Do I Need Expert Assistance for Band Joist Installation?

While experienced DIYers can install band joists,it is always advisable to seek professional help for complex installations.

They can ensure proper installation and adherence to local building codes.

V Susan
Hi! I'm Susan. I am passionate about woodworking, general DIY and home improvement. If you'd like to connect with me or talk about something you like at mellowpine, drop me a mail at susan@mellowpine.com