Expansion Joint Repair

Expansion joints are designed to move. When the cover system fails to accommodate that movement, the joint becomes the most reliable leak path on the roof.

Expansion joints in commercial buildings are engineered movement accommodation - they allow the building's structure to expand, contract, and settle without transferring stress to the adjacent structure. On commercial roofs, expansion joints typically run along the intersection of building sections, along the length of long structural bays, and at the separation between a building addition and the original structure. Every expansion joint is a designed gap in the roof system, and every designed gap requires a waterproofing cover that can move with the building without losing its watertight integrity.

Atlanta commercial buildings experience more expansion joint movement than comparable buildings in many other markets. The city's thermal cycling - summer rooftop surface temperatures above 140°F in Midtown and Downtown Atlanta dropping to below freezing on winter nights - drives expansion and contraction in structural members and roofing assemblies that is among the most extreme in the Southeast. The Piedmont granite geology underlying most of the metro produces differential foundation settlement in adjacent building sections that adds vertical and lateral movement to the thermal cycling. Expansion joints in Atlanta buildings move more, more often, than the manufacturer's design assumptions for static structures in moderate climates.

We repair and replace expansion joint covers on commercial flat roofs as a standalone scope item and as part of larger roof restoration or replacement projects. The work is typically driven by two failure modes: elastomeric joint covers that have cracked or split after losing flexibility through UV degradation and thermal fatigue, and metal joint covers that have separated at seam joints or anchor points because the expansion or contraction of the building has exceeded the cover's design range. In either case, the failed joint cover is the most direct water entry path into the building - repair is urgent, not deferrable.

Elastomeric membrane covers: Flexible thermoplastic or thermoset joint covers - TPO bellows covers, EPDM bellows, or Hypalon bellows - are designed to flex through the joint's movement range without cracking. They fail in Atlanta conditions when UV degradation makes the elastomer brittle - the bellows that was designed to flex simply cracks instead. Aged EPDM bellows on Atlanta's 1990s office buildings is the most common example: the material surface chalks and cracks, particularly at the fold points of the bellows where stress concentrates. Once cracked, the cover allows direct water entry regardless of flashing condition.

Metal joint covers: Pre-formed aluminum or stainless steel expansion joint covers are common on larger Atlanta commercial buildings - convention facilities, healthcare campuses, and multi-section office buildings. Metal covers fail at two points: the anchor flanges where the cover is mechanically fastened to the adjacent roof sections, and the center bellows or slip joint that accommodates movement. If building movement exceeds the cover's design range, the anchor flanges pull away from the roof substrate or the center element deforms beyond its capacity. Metal cover failures at the Cobb County convention facilities and healthcare campuses along I-285 are typically movement-related rather than UV-degradation failures.

Fluid-applied expansion joint waterproofing: Some older Atlanta commercial buildings have expansion joints that were waterproofed with a fluid-applied elastomeric coating over a reinforcing fabric bridge rather than a pre-formed cover. These systems fail when the fabric bridge tears at the center of the joint, typically because building movement exceeded the fabric's capacity, or when the fluid-applied coating delaminates from the adjacent membrane because the substrate was not properly primed at installation. Fluid-applied joint repairs require the same fabric bridge and coating system as the original - substituting a different product type without verifying compatibility with the adjacent membrane system typically produces premature failure.