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Construction glossary · Wood framing

What is rim joistin construction?

A rim joist, also called a band joist, is the joist that runs around the outside edge of a floor frame, capping the ends of the floor joists and closing the perimeter. It sits on the sill plate or top plate and ties the floor system together. Its quantity is simply the floor perimeter in linear feet plus waste.

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Updated June 2026 · Reviewed by the Ruh construction team

Aka Band joistDepth Matches floor joistsSits on Sill plateRole Caps joist ends

Rim joist closes floor frame, caps joist ends

Continuous at perimeterWraps full floor edgeJoist ends and sill plate
The definition

Rim joist (band joist), explained.

A rim joist (band joist) is the perimeter member of a platform floor in light-frame construction. It runs continuously around the edge of the floor, the floor joists butt into it or hang off it, and it transfers floor and wall loads down to the sill plate over the foundation or to the top plate of the wall below. The rim closes the joist bays, provides backing for the subfloor edge and the wall above, and resists joist rollover. It is usually cut from the same depth stock as the floor joists, 2x8, 2x10, or 2x12 dimensional lumber, or it may be an engineered rim board where I-joists are used so depths match. On exterior walls the rim is part of the load path and often gets blocking and the wall's bottom plate nailed through it. Estimators size the rim by the building's floor perimeter, since it wraps the full outside edge of the deck.

How it is measured

Rim joist is measured in linear feet equal to the floor perimeter, read off the foundation plan or floor framing plan outline. Add up the outside dimensions of all exterior walls to get the perimeter, then add waste for corners and splices, typically 5 to 10 percent. Convert to board count by dividing perimeter by the stock length you are buying, usually 16 ft, and round up. For board feet, multiply linear feet by the board feet per linear foot of the chosen stock. Match the rim depth to the floor joist depth shown in the framing notes. On the plan the rim follows the heavy line at the deck edge; watch for cantilevers and bump-outs that add perimeter.

Worked example

A worked Rim joist (band joist) example.

Worked example

Take a rectangular floor of 40 ft x 28 ft. Perimeter = 2 x 40 + 2 x 28 = 80 + 56 = 136 lf of rim joist. Buying 16 ft 2x10 stock: 136 / 16 = 8.5, round up to 9 boards with no waste factor. Add 8 percent waste for splices and corners: 136 x 1.08 = 146.88 lf, which at 16 ft per board is 9.18, round up to 10 boards. For board feet, a 2x10 carries 1.667 bf per linear foot (nominal 2 x 10 / 12 = 20 / 12), so 136 lf x 1.667 = 227 bf at takeoff, or about 245 bf with 8 percent waste. So the rim for this deck is 136 lf net, roughly 10 sticks of 16 ft 2x10, about 227 to 245 bf depending on whether you price net or with waste.

How Ruh handles it

How Ruh handles Rim joist (band joist).

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Rim joist (band joist): frequently asked questions

Is a rim joist the same as a band joist?+

Yes. Rim joist and band joist are the same member, the joist that wraps the perimeter of the floor and caps the ends of the field joists. Some regions also call it a rim board, especially the engineered version used with I-joists.

What size is a rim joist?+

It matches the floor joist depth so the deck stays flat, commonly 2x8, 2x10, or 2x12 dimensional lumber. With I-joist floors you use an engineered rim board of the same depth so the bearing lines up.

How do I estimate rim joist quantity?+

Sum the building's exterior perimeter in linear feet from the floor plan, add 5 to 10 percent waste, then divide by your stock length and round up. A 40 ft x 28 ft floor is 136 lf of rim.

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Related terms

Sill plateSubfloorBlockingI-joistJoistlaminated veneer lumber

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Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.

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