What is an Expansion Joint?


The expansion joint in the above photo runs through the brick pavers as well as through the structural slab that supports the plaza. Waterproofing is handled on the structural slab by a buried waterproofing membrane. The expansion joint bisects all of the building elements including the structural slab, membrane, and wear course (bricks). Sealing this type of expansion joint requires a specialized expansion joint system. The FP-series of plaza deck expansion joints from EMSEAL, ensure that the joint is properly integrated with the waterproofing membrane while accommodating structural expansion and contraction movement of the split-slab plaza deck assembly.

In building construction, an expansion joint is a mid-structure separation designed to relieve stress on building materials caused by building movement induced by:

  • thermal expansion and contraction caused by temperature changes,
  • sway caused by wind
  • seismic events
  • static load deflection
  • live load deflection

Because the joint bisects the entire structure, it marks a gap through all building assemblies–wallsdecksplazas or split-slab concoursesfoundation floors and wallsroofs, planters, and green roofsfire-rated demising walls and floorsinterior floors; etc.  This gap must be filled to restore the waterproofing, fire proofing, sound proofing, air barrier, roof membrane, trafficable surface and other functions of the building elements it bisects.

Expansion joint systems are used to bridge the gap and restore building assembly functions while accommodating expected movements.

The term “movement joint” has been widely adopted in preference to “expansion joint” as it more appropriately encompasses the fact that building movement results in both compression and expansion of the material installed.

For example, when a structure heats up, the building materials from which it is built expand.  This causes the “expansion joint” to close down, thereby compressing the expansion joint system installed in the gap.


The above is a wall expansion joint. This structural opening bisects not only the facade but the structural building elements as well. While accommodating movement, expansion joint materials used to fill wall expansion joints must restore the intended functions of the facade and structural building elements. These functions include: waterproofing, resisting hurricane-force wind and water, air-barrier sealing, sound proofing, and in many cases fire proofing. Additionally, because wall expansion joint materials interface with facade materials that should not be penetrated with fasteners, non-invasive anchoring is a desirable feature.

Conversely, when the temperature drops, the materials cool causing the joint gap to open.  This requires the expansion joint material to expand to follow the joint movement.




NOTE: The definitions of terms and terminology herein are rooted in the context of use in the field of construction-related joint sealing in EMSEAL’s experience.  They are provided with the intent of offering a fuller understanding of the context of their usage. Any suggestions or questions regarding interpretation are welcome and should be directed to content@emseal.com. Thank you.