A band joist is a structural component that provides lateral support for joists, to prevent them from undergoing deformations under the weight of load-bearing walls that rest on them.
In a floor frame system, band joists are fitted perpendicular to the joist ends.
What is a Band Joist?
In residential construction, joists play a vital role in providing stability to floors and roofs. Joists differ in name and functioning on the bases of their positioning.
Floor joists and roof joists are used to create load-bearing frames for the floors and roofs of a house.
They are typically made from lumber and are spaced closely together (a minimum of 16 inches).
Band joists are installed perpendicular to floor and ceiling joists, also constituting the longitudinal sides of the perimeter of a floor system.
Band joists are visible from the outside of a house under construction, as solid lumber blocks running along the frame of a floor system.
The primary function of a band joist is to provide lateral support to other joist members in a floor or ceiling, consequently increasing their strength and stability.
Floor and ceiling joists are normally connected to band joists by having their ends nailed in.
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.
Sill plates form the base of a floor frame and lie on top of the foundation wall.
What Are Band Joists Used For?
Band joists are the main lateral supports for other joists. Every floor or roof joist is nailed into a band joist. This nailing helps to keep the floor joists intact in an upright position.
The frame thus constructed has sufficient strength and stability to support loads on top of it. In this way, the integrity of a floor or ceiling joist frame system is kept intact.
If you are to build a deck using floor joists, it is essential that band joists be used to create the boundary of that deck. Band joists run throughout the perimeter of a floor deck.
They keep the floor joists from changing their positioning. Otherwise, the joists would tip and lose their durability.
Band joists rest on top of foundation walls. In some cases, band joists do not carry any loads as there are no structures constructed over them.
But, in most cases, walls are erected on top of band joists. These exterior walls make the band joists load bearing. Stairs and railing may also be supported by band joists.
Band joists are chunky blocks that provide sufficient area for nailing.
The joist frame configuration is thus strengthened by the nailing action and the house in return becomes sturdy.
Exterior sheathing is provided to band joists that act as a nailing base and provides protective covering.
If your structure is non-residential and is intended to bear heavy loads then you should consider a floor truss system as opposed to a traditional floor joist.
Band Joist Size & Material
What are Band Joists Made From?
The composition of band joists is usually the same as other typical joists.
They are either fashioned using lumber or steel, depending on the region and plan requirements.
In some cases, the rim is made out of steel while the inner floor joists are made of wood.
Engineered wood may also be used to build joists.
These are larger in size than normal lumber and have more strength and durability.
Architects and engineers get to decide which material composition is more suitable for their designs.
What is the size of a Band Joist?
Talking about the dimensions of a band joist, they are usually the same size as other joists. They are kept in line along the top and bottom with floor joists.
In certain cases, however, band joists are constructed to be larger than floor joists. Typically for bearing more loads.
To increase the strength and durability of a floor frame and to reduce the bounce on them, it's generally better to increase the area of band joists.
This can be done by installing double rim joists across the longitudinal sides of the perimeter.
Alternatively, you can also block or bridge joists to reduce floor bouncing.
The effectiveness of a structural member in construction depends greatly its dimensions and the material that constitutes it.
What is the difference between a Band Joist and Rim Joist?
The terms band joists and rim joists are interchangeable and are both used for the same structural members.
When taking into consideration the joists on the longitudinal sides of the perimeter of the floor frame, the term rim joist is used.
On the other hand, when referring to longitudinal side joists along with the shorter end joists collectively, the term band joists is used.
How are Band Joists Installed?
Band joists are installed perpendicular to standard joists, which means they run parallel to the longer sides of a house.
While standard joists run along the shorter sides of the house. Each standard joist is connected to a band joist by having three nails driven through the face of a band joist.
The first and the last standard joist is known as an end joist.
Where are Band Joists Provided?
Band joists rest on top of sill plates, which provide base support to the joists. Band joists are nailed into sill plates using framing nails.
The whole configuration of standard joists, sill plates, and band joists rests on top foundation walls.
Can Band Joists be Reinforced?
Metal reinforcement may be provided to strengthen these connections.
This strengthening reduces the deformations in the joists that may lead to floor separation under the action of high wind and seismic activity.
Should You Insulate Band Joists?
Insulation is a great way to regulate the temperature of houses. It keeps a house warm in winter and cold in summer.
This method of temperature regulation reduces the need for other alternative approaches thus keeping energy costs to a minimum.
Insulation in a band joist can be provided in the following ways:
- By covering the interior face of a band joist above the foundation wall with insulating material.
- Install a rigid foam insulation board on the exterior walls down enough to cover the band joists.
- Cut several pieces of fiberglass insulation and place them into the cavities of band joists. The insulation material will be held together by friction.
The insulation must be impermeable to air too because band joists are prone to a phenomenon called drafting.
Drafts are caused by the replacement of warm air from indoors with cold air from the outside.
This reduces the effectiveness of a heating system considerably, consequently increasing heating costs.
Which Material is Used for Insulating Band Joists?
Fiberglass is an easy-to-use insulating material. It can easily be cut into the required proportions.
But using fiberglass may lead to mold problems as it can let air and moisture through.
To prevent mold, rigid foam should be applied at the edges to keep air and moisture out.
On the other hand, spray foam provides better covering but is tedious to apply.
The best option is to provide insulation during the construction phase of a house.
Band joists along all the floors should be insulated. Doing this after constructing the house can be difficult due to the drywall blocking access.
Is Insulating Band Joists Worth It?
Efficient insulation along the band joists helps in regulating the temperature of a house.
It also eliminates moisture and air leaks. A strong thermal blanket is formed around the frame which forms an envelope and surrounds the building.
This insulation helps conserve heat and thereby reduces heating costs.
Thus, it is safe to say that insulating band joists is well worth it.
Do I Need a Band Joist?
If you are constructing a house or any other structure that requires a floor, you will need to use band joists to create the edge of your floor frames.
Residential as well as commercial buildings will mostly require a framed floor. In some instances, the band joists may even be required to bear heavy loads. For this reason, their strength must be ensured beforehand.
In decks, a band joist helps secure railing posts. In houses, a wall can be erected on top of band joists. They may also be used to anchor stairs and railings.
By applying proper insulation to band joists, energy costs can be reduced drastically. The insulation helps keep the house warm in winters and cold in summers.
Can you Drill through a Band Joist?
Yes, holes can be drilled into band joists. The pipes, vent and wires are commonly passed through a band joist by drilling a hole through the band.
If the hole is not significantly large, it will not affect the strength of the band joists.
After the pipes and wires have been installed through the holes, insulation is provided around them. Spray foams are used to seal any gaps left in the hole.
Spraying foam also keeps out pests and insects.
Commonly, holes of 1-1/2 in diameter are drilled throughout the web. Larger holes should be drilled towards the middle of the joist section and not the ends.
Can Band Joists be Replaced?
In case of any damage due to weather action or insects, it is easy to replace a section of a band joist.
This is done from the outside of a building, by removing the sheathing. After the band joists are exposed, the hangers and bolts are removed.
The wires and pipes may also need to be put aside while replacing a band joist.
Temporary support may need to be set up in some cases, while the replacement is ongoing.
Once the band is ready, cut out the damaged section and replace them with materials.
Fix the new sections by hangers and bolts.
Pass the wires and pipes through the new section by drilling new holes. Finally provide insulation where required.
What are the Advantages of using Band Joists?
Band joists are an integral part of residential construction.
- Band joists provide support to standard joists in a floor frame and bear the loads of exterior walls.
- They can be installed quite conveniently and in case of any faults, be replaced with ease.
- Holes can easily be drilled into band joists, allowing passage for wires and ducts.
- With proper insulation, band joists become an excellent means to conserve energy and reduce energy costs.
- They are commonly made of lumber or engineered wood making them cheap and readily available.
- Steel band joists provide extra strength and support to frames.
Frequently Asked Questions (FAQ)
Should rim joists be doubled?
In order to increase the strength and durability of the perimeter in a floor frame or deck frame and to reduce the bounce on them, it is advised to increase the area of band joists. This can be done by installing double rim joists across the longitudinal sides of the perimeter.
How much does it cost to repair a rim joist?
The total cost to repair a band joist depends on the extent of damage done to it and the ease with which it could be safely removed and replaced. On average, the cost for repair for a single band joist lies between 100$-300$. Repairs may also be needed for the floors themselves having developed permanent deformations due to the faulty joists. The expenditure could then rise to 1000$-3000$
How thick should rim joist insulation be?
While using fibreglass insulation, 10-inch-long sections should be cut with a depth of 6 inches. With these proportions, the insulation can be fitted into the cavities of band joists and will then be held up by friction. It is to be noted that the size of the insulation should be kept a little larger than the size of the cavity.
Are Band Joists Load Bearing?
Band joists may or may not be load bearing depending upon the project. If an exterior wall is to be erected on top band joists or a staircase is to be installed in connection with the band joists, then the band joists become load bearing. Meanwhile, if no structure is constructed on top of band joists, they will bear no loads.