Expansion joints in Salt Lake City commercial buildings absorb thermal movement across one of the most extreme temperature ranges of any major U.S. market - July surface temperatures above 160 degrees and January ambient temperatures below zero. A cover system that cannot accommodate that range will fail at the center of the bellows. We repair or replace the cover with a system that is specified for the movement range the building actually experiences.

Expansion joints in commercial buildings exist because the thermal and structural movement a large building experiences cannot be absorbed by a continuous membrane without cracking or tearing. The joint is a designed gap - typically one to three inches wide - that allows adjacent building sections to move relative to each other. The roof expansion joint cover spans that gap at the roof surface and keeps water out while the joint opens and closes beneath it. In Salt Lake City's climate, the movement demand on that cover system is among the most severe of any inland metropolitan market.

Salt Lake City's temperature range - from sustained winter lows below zero to peak summer surface temperatures approaching 165 degrees Fahrenheit on dark membrane surfaces - produces thermal movement in building structural elements that exceeds the design assumptions used in many original joint specifications. A building designed in the 1980s with a joint cover specified for a moderate thermal range may have been operating outside that range for decades. Add the freeze-thaw cycling that occurs 80 to 120 times per year as the cover material contracts and expands through each cycle, and the bellows cover accumulates fatigue damage at a rate that often surprises building owners who have not had the joint system inspected.

We repair and replace expansion joint covers on Wasatch Front commercial buildings using EPDM and TPO bellows systems specified for the actual movement range the building experiences - not a conservative estimate derived from climate tables, but a measured range based on joint-width readings at different times of year. Every expansion joint repair we do begins with that measurement.

EPDM and TPO Bellows Cover Systems for Utah Conditions

EPDM bellows covers are the most common system on Salt Lake City commercial buildings constructed through the 1990s. The bellows - a flexible loop of EPDM that spans the joint opening - accommodates horizontal movement by extending and compressing. Cold-temperature flexibility is a key performance criterion on Wasatch Front buildings: EPDM maintains flexibility at temperatures down to minus 40 degrees Fahrenheit, which is relevant in Utah's coldest January conditions. When the bellows tears or the termination bars separate from the surrounding membrane through freeze-thaw cycling, the joint leaks at the opening of the gap.

TPO heat-weldable expansion joint covers are the current standard specification for buildings on TPO membrane systems. The cover is heat-welded to the field membrane on both sides of the joint, with a pre-formed TPO bellows spanning the gap. Because the cover is welded, it integrates with the membrane system cleanly and eliminates the termination bar-to-membrane interface as a freeze-thaw failure point. On buildings where we are replacing a failed EPDM bellows cover on an existing TPO roof, we specify the TPO heat-weldable cover system to consolidate the assembly into one membrane type.

For joints on buildings with existing modified bitumen or BUR systems, we use a preformed cover in a modified bitumen-compatible formulation, torched into the surrounding membrane. These systems require more careful movement range estimation in the SLC market - if the cover is undersized for the actual thermal movement range on a Utah building, it tears at the center of the bellows within one to two seasons.