2.9
Movement Joints in Buildings
Movement joints in buildings are essential design elements that accommodate inevitable motions caused by various factors such as temperature changes,…
Slight movements in buildings can occur during the expansion of building units exposed to moisture or the upward heaving of foundations when water in the soil expands while freezing.
Movements may form cracks in the building; movement joints such as working joints, structure enclosure joints, surface divider joints, and building separation joints are provided to avoid this.
Working joints are used in shingled roofs, where small strips are assembled in an overlapping pattern, tolerating slight movements without any distress.
In a cavity wall, the soft joint provided under the shelf angle supporting the non-structural exterior wythe is an example of a structure enclosure joint.
Surface divider joints include isolation joints, expansion joints, and control joints.
When new additions are made to an existing building, isolation joints are provided, enabling the movement of the new materials without impacting the existing building.
Expansion joints are open slots designed to allow the expansion of building materials, while control joints are lines of weakness created where cracks may occur when building materials shrink.
Lastly, building separation joints subdivide complex building structures into discrete segments that can be independent of each other's movements.
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Q1: What causes movements in buildings that require joints?
Building movements occur from moisture exposure causing expansion, foundation heaving when soil water freezes, and thermal fluctuations. These movements can form cracks unless accommodated by movement joints. Temperature changes, moisture content variations, and structural deflections are primary drivers of these inevitable motions that must be managed during design and construction.
Q2: How do working joints function in shingled roofs?
Working joints in shingled roofs use small strips assembled in an overlapping pattern that tolerate slight movements without distress. This simple joint type is integrated during construction and allows thermal and moisture movements to occur freely. Similar applications include wood bevel siding, which accommodates material movement through overlapping design.
Q3: What is the purpose of structure enclosure joints in cavity walls?
Structure enclosure joints separate structural from nonstructural elements to prevent load transfer that could cause damage. In cavity walls, soft joints are placed under shelf angles supporting the non-structural exterior wythe. This design prevents deflection and stress concentration, protecting both structural and nonstructural components from harmful interactions.
Q4: How do isolation joints differ from control joints?
Isolation joints enable independent movement between new and existing materials without interference, commonly used during renovations. Control joints create predetermined lines of weakness where cracks occur in a controlled manner, seen in concrete sidewalks and plaster walls. Both manage material movement but serve different purposes: isolation prevents interaction, while control directs cracking.
Q5: What role do expansion joints play in masonry systems?
Expansion joints are open slots designed to allow building materials to expand and contract freely. They accommodate material movement evident in brick walls and curtain wall systems, preventing stress buildup. These joints work alongside expansion and contraction in masonry walls to manage dimensional changes caused by temperature and moisture variations.
Q6: How do building separation joints subdivide complex structures?
Building separation joints divide complex building structures into discrete segments that move independently of each other. These joints are categorized into volume-change joints, settlement joints, and seismic separation joints, each addressing specific structural movement challenges. This subdivision prevents one section's movement from damaging adjacent sections.
Q7: Why are movement joints essential in building design?
Movement joints prevent unsightly or dangerous damage caused by inevitable building motions. Without proper joints, thermal expansion, moisture absorption, and foundation heaving create cracks and structural stress. Movement joints accommodate these stresses by allowing materials to move freely, maintaining building integrity and safety throughout its lifespan.