As building envelope consultants, we are increasingly tracking not just weather events but their cumulative effect on long-term building performance. One such stressor is the freeze–thaw cycle—a phenomenon where outdoor temperatures fluctuate above and below 32°F within the same 24-hour period. These cycles may appear routine, but over time they have profound consequences on material integrity, building maintenance costs, and occupant safety.
Recent analysis of hourly weather data from 2010 to 2025 shows a noticeable decline in freeze–thaw cycles across both New York City and Boston. In Boston, the annual count has dropped from approximately 70 events in 2010 to under 50 by 2024. New York City shows a similar trend, falling from around 65 to just over 40 cycles per year. This reduction is consistent with regional warming patterns documented in ASHRAE Climate Data reports and NOAA climate summaries.
Yet despite the reduction, the risk posed by remaining freeze–thaw events is not diminishing—especially as they become less predictable and often more abrupt. Here’s how the continued occurrence of freeze–thaw cycles influences key building materials and systems:
1. Masonry and Terra Cotta Systems
Masonry assemblies—especially those using clay brick or terra cotta—are particularly vulnerable. When moisture penetrates the outer wythes and freezes, it expands by about 9%, exerting internal pressure that can lead to spalling, cracking, and delamination. According to the American Concrete Institute (ACI 201.1R-08), recurring freeze–thaw action is one of the primary drivers of surface scaling and joint degradation in exterior concrete and masonry walls.
Historic structures constructed with terra cotta cladding are particularly susceptible due to aged or failed mortar joints, clogged weeps, and early 20th-century anchorage designs that lack corrosion resistance. A proactive inspection and repointing schedule—especially using compatible materials that are similar in strength is critical.
2. Roofing Assemblies
Low-slope roofing systems experience different but equally damaging effects. Inadequate drainage, membrane breaches, and aging insulation can allow water infiltration, or lead to vapor drive, which, when frozen, causes blistering, delamination of membrane plies, and further degradation of insulation R-value. According to ACI 546R-04, freeze–thaw damage in concrete roof decks may also initiate microcracking that leads to corrosion of embedded reinforcement. This becomes an even larger problem when combined with cinder concrete that are so prevalent in early & mid 20th century buildings.
3. Windows and Glazing Systems
Windows, especially older steel-framed or poorly flashed assemblies, often develop failures at transitions and interfaces. When temperatures swing across the freezing point, moisture that has entered the glazing pocket or subsill can freeze, causing sealants to fail. This is often observed as condensation, fogging, or increased air infiltration. Window perimeter sealants and setting blocks must be selected based on tested compatibility with both the substrates and expected movement due to thermal cycling.
4. Concrete and Structural Framing
Concrete subject to repeated freeze–thaw cycles without proper air entrainment can exhibit scaling, popouts, and surface delamination. In their Guide to Durable Concrete, ACI emphasizes that durable exterior concrete in northern climates must include proper air void systems and avoid saturation prior to freezing. Buildings with exposed-grade slabs, plaza decks, or structural balconies must be routinely inspected for early signs of distress, especially if sealers or coatings have deteriorated, or were value engineered out of the initial design, as is so often the case!
Conclusion: Why Freeze–Thaw Still Matters
Even as regional climate data suggests a decline in annual freeze–thaw events, their ongoing presence—and their severity—pose a real and quantifiable threat to aging and thermally inefficient buildings. For building owners, facility managers, and preservation professionals, the right strategy is not to hope these cycles go away, but to understand where and how they exert stress on enclosures and proactively intervene.
Annual condition assessments, strategic material selection, and investment in resilient detailing at transitions (parapets, window heads, sills, control joints) remain the most effective tools in the building owner’s toolbox.
Further Thoughts:
If the freeze-thaw cycles in the northeast US have decreased due to the gradual increase in temperatures, I wonder if the number have increased for our friends in Canada, and if so, does that mean their buildings will degrade more quickly than they have seen in the past?
| Freeze–Thaw Cycle Estimates (2010–2025) | ||
| Year | New York City | Boston |
| 2010 | ~65 | ~70 |
| 2011 | ~63 | ~68 |
| 2012 | ~60 | ~66 |
| 2013 | ~62 | ~67 |
| 2014 | ~64 | ~69 |
| 2015 | ~61 | ~65 |
| 2016 | ~59 | ~63 |
| 2017 | ~58 | ~62 |
| 2018 | ~56 | ~60 |
| 2019 | ~54 | ~58 |
| 2020 | ~52 | ~56 |
| 2021 | ~50 | ~54 |
| 2022 | ~48 | ~52 |
| 2023 | ~46 | ~50 |
| 2024 | ~44 | ~48 |
| 2025* | ~42 | ~46 |
| *2025 data is projected based on trends observed in the first half of the year. | ||
Kevin M. Duffy
Principal
Duffy Engineering
