Expansion Joint and Control Joint Detailing: Location, Sizing, Cover Assemblies, and Fire Rating Continuity

Detailing expansion joints and control joints in construction documentation, including placement criteria based on structural configuration and movement, joint sizing and sealant selection, cover assembly options, and maintaining fire-resistance-rated assembly continuity across joints.

ARE · Project Development & Documentation

Overview

Buildings move. Temperature swings, moisture changes, structural loading, and seismic events all produce forces that want to crack, buckle, or split assemblies apart. Movement joints are the architect's primary tool for controlling where and how that movement happens, and documenting them correctly on construction drawings is one of the most detail-intensive tasks in the PDD division.

This topic covers four interlocking concerns you'll face on the ARE and in practice. First, location: where to place expansion joints and control joints based on material behavior, structural configuration, and stress concentration points. Second, sizing: calculating joint widths, selecting sealant classes, and specifying backer rod dimensions to accommodate predicted movement. Third, cover assemblies: choosing and detailing the visible components that protect joints while allowing movement. Fourth, fire rating continuity: ensuring that every joint passing through a fire-resistance-rated assembly gets proper firestopping so the rating isn't broken.

The exam expects you to analyze non-standard conditions, evaluate competing placement strategies, and make decisions about which joint type and detail approach best serves the project's constructability, performance, and code compliance requirements. These joints are among the most frequently misunderstood elements in construction documents. Getting the location, spacing, and detailing right prevents cracking, leaking, and material failure that shows up months or years after occupancy and becomes the architect's liability.

Essential

Understanding the Joint Types Before you can detail movement joints, you need to know what each type does and when to specify it. Getting these confused on the exam will cost you points fast. An expansion joint separates brick masonry into segments, preventing cracking from cumulative thermal expansion, moisture growth, elastic deformation, and creep. These joints accommodate material that grows over time. The joint is a continuous, unobstructed opening through the brick wythe, filled with highly compressible material and sealed with elastomeric sealant. A control joint works differently. It creates a deliberate plane of weakness in concrete or concrete masonry (CMU) construction so that shrinkage cracks form at predetermined, controlled locations rather than randomly. Control joints are typically partial-depth indentations or vertical gaps filled with less compressible materials. While expansion joints handle growth, control joints handle shrinkage. A building expansion joint is the big one.

Professional

A 12-story mixed-use building with a brick veneer facade presents the design team with a compounding set of movement joint decisions. The ground floor has a storefront system transitioning to brick veneer above, with shelf angles at every third floor. The architect faces the question of whether to maintain continuous vertical expansion joints through the shelf angle locations or offset them. The answer depends on the differential movement between the structural frame and the cladding. Each shelf angle creates a horizontal expansion joint that allows independent vertical movement of the brick panels above and below. Vertical expansion joints should align across horizontal joints when possible, but structural geometry sometimes forces offsets. Documenting these conditions requires enlarged detail drawings at a minimum 3 in. scale showing the sealant profile, backer rod placement, and how the vertical and horizontal joints intersect.

TLDR

Expansion joints handle growth (brick). Control joints handle shrinkage (CMU/concrete). They are NOT interchangeable.
Vertical expansion joint max spacing: 25 ft (no openings), 20 ft (with openings), 15 ft (parapets).
Place joints at corners (within 2 ft preferred), offsets, height changes, material transitions, and support condition changes.
Corner rule: combined distances from corner to first joint on each wall cannot exceed the standard straight-wall spacing.
Sealants: ASTM C920, Grade NS, Use M. Class 50 or 100/50 recommended. Silicone preferred for brick.
Backer rod: 25% larger than joint width. Sealant depth: half the joint width, minimum 1/4 in.
Horizontal joints at shelf angles need minimum 1/4 in. gap with compressible fill.
Lipped brick: two-thirds bearing on shelf angle, one-third max overhang, lip min 1/2 in.
Fire rating: every joint through a rated assembly needs firestopping that allows movement. F-Rating (flame), T-Rating (325 degrees F rise), L-Rating (air leakage).
Curtain wall perimeter firestop tested per ASTM E2307; voids can be 1 to 12 in. or wider.

ELI5

Think of a really long sidewalk on a hot summer day. Without those little grooves cut into the concrete, the whole slab would crack randomly as it expands in the heat. Those grooves are movement joints. Buildings need the same thing, just way more complex. Buildings are made of different materials that all expand and shrink at different rates when the temperature changes or when they absorb moisture. Brick actually grows slightly over its lifetime. Concrete shrinks as it cures. Steel expands and contracts with temperature. If you lock all these materials together without any relief, something has to give, and that something is usually a crack. So architects put in special gaps. For brick walls, these are called expansion joints because they give the brick room to expand. For concrete block walls, they're called control joints because they control where the inevitable shrinkage cracks will happen.

AREProject Development & Documentation

Expansion Joint and Control Joint Detailing: Location, Sizing, Cover Assemblies, and Fire Rating Continuity

2 min read213 words

Why Movement Joints Make or Break Your Documentation

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