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Construction glossary · Wood framing

What is blockingin construction?

Blocking is short pieces of framing lumber cut and installed between studs, joists, or rafters to brace the frame, fill gaps, back up finishes, or stop fire and air movement. It is the same dimension lumber as the members it sits between and is taken off in linear feet. Fire blocking, solid blocking for structural bracing, and nailer blocking for finishes are common types.

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Updated June 2026 · Reviewed by the Ruh construction team

Block length ~14-1/2 in. (16 o.c.)Purpose Fire stop, bracing, backingTakeoff 1 LF per LF wall rowCode Fire blocks at 10 ft max

Mid-height blocking between studs

Between studs at 16 in. o…Row at mid-wall heightLateral / fire stop member
The definition

Blocking, explained.

Blocking is any short framing member installed perpendicular between the primary members of a frame. In a floor it runs between joists as solid blocking or bridging to keep joists from rolling and to share load; in a wall it goes between studs as backing for cabinets, grab bars, handrails, and panel edges, and as fire blocking that closes concealed vertical and horizontal voids so a fire cannot run the cavity. In a roof it ties rafters or truss bottom chords and provides a nailer at eaves. The lumber matches the surrounding members, so 2x10 joists get 2x10 blocking. Estimators take it off in linear feet because the pieces vary in length but cut from the same stock, then convert to board feet to order and price the actual lumber. Quantity is driven by the joist or stud spacing, the number of rows, and any code-required fire blocking at floor lines, soffits, and stair stringers.

How it is measured

Blocking is taken off in linear feet, then converted to board feet for ordering and pricing. On the framing plan and details, find the blocking rows: mid-span solid blocking in floor joists, fire blocking at the top and bottom of stud walls and at 10 ft horizontal intervals, and backing for finishes from the architectural details. For a joist bay, the blocking length per row equals the building or bay width, and the count of pieces equals the number of bays. Multiply length by number of rows for total linear feet, then convert linear feet to board feet using the member size. Read the lumber size off the joist or stud callout, since blocking matches it.

Worked example

A worked blocking example.

Worked example

A joist bay layout 24 ft wide with joists at 16 in OC. One row of solid blocking across the bay is 24 lf. The plan calls for fire blocking at the wall line plus one mid-span row of solid blocking, so 24 lf + 24 lf = 48 lf of blocking total. The joists are 2x10, so convert to board feet: board feet per linear foot of 2x10 = (nominal 2 in x 10 in) / 12 = 20 / 12 = 1.667 bf per lf. Total = 48 lf x 1.667 bf/lf = 80 board feet. At an illustrative 0.85 dollars per board foot, material is 80 x 0.85 = 68 dollars for the blocking lumber before fasteners.

How Ruh handles it

How Ruh handles blocking.

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Blocking: frequently asked questions

How do I take off blocking, in linear feet or board feet?+

Take it off in linear feet first since the pieces cut from the same stock as the joists or studs. Then convert linear feet to board feet using the member size to order and price the actual lumber.

What is the difference between fire blocking and solid blocking?+

Fire blocking closes concealed cavities so flame and air cannot travel the void, required at floor lines, soffits, and stairs. Solid blocking is structural, set between joists to stop rolling and share load. Both are taken off in linear feet.

How many board feet is 48 lf of 2x10 blocking?+

A 2x10 is 20 / 12 = 1.667 board feet per linear foot. So 48 lf x 1.667 = 80 board feet. Order to the next stock length and add a small cutting allowance.

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Related terms

Fire blockingSheathingRafterRim joist (band joist)OSB (oriented strand board)JoistStudSleeper

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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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