FAILURES
Deborah Slaton and David S. Patterson, AIA
The effects of cold on buildings are widely varied.* One of the more extreme examples of damage is cracking and spalling of masonry when water trapped within the pores of masonry units expands with cyclic freezing and thawing. Distress can also occur when construction materials are employed at or below freezing temperatures or the weather becomes wintry during installation or curing. For example, if mortar freezes during curing, it will crack and fail prematurely in service. Additionally, the serviceability of sealants and coatings may be affected by cold temperatures during installation or curing—application of these materials in chilly weather can also be affected by substrate conditions such as the formation of condensation or ice on the bond surface.
Photo courtesy WJE
The problems created by sub-freezing weather also extend to glazing units, especially where single glazing is present, although condensation can form on the interior surface of insulating glass units (IGUs) and metal window frames during colder weather conditions. When exterior temperatures are very cold and the temperature of the glass (and/or frame) is at or below the dewpoint of the space, moisture from the warmer, more humid interior air condenses on the inside of the window (or door) assembly. When the temperature of the glass falls below 0 C (32 F), this liquid water freezes, resulting in the formation of frost or ice on the glass surface. Frost and ice formation on the interior face of fenestration can range from a few decorative crystals to a thick covering of ice that is difficult to remove. In extreme cases where ice formation occurs, as exterior temperatures rise and the ice melts, damage to the sash and frame as well as adjacent interior finish surfaces can result if unaddressed quickly. Repeated exposure to moisture from condensation can lead to paint failures, rotting of wood window (or door) components and wall framing members, damage to interior finishes, and formation of organic growth on moisture-sensitive materials within the wall assembly.
Replacement of glazing, or entire window/door assemblies, with thermally improved units is often not a cost-effective or appropriate option on smaller buildings, residences, or historic structures. Some alternative options to reduce the potential for condensation include:
- ensure windows close securely, and that weatherstripping is effective in limiting the infiltration of air;
- repair/replace sealant at the window perimeter as needed to provide an intact seal;
- reduce the relative humidity (RH) in the interior space, including improved ventilation of bathroom, kitchen, and laundry spaces;
- provide a source of warm air near the window/door assembly;
- eliminate window treatments by isolating and restricting airflow across the interior plane of the assembly;
- install exterior storm windows, which can be removed during warm weather (those of us of a certain age growing up in the north will remember, perhaps nostalgically, wood-framed storm windows with three holes and a rotating wood closure in the bottom rail for ventilation); and
- install airtight (and typically removable) interior storm windows to prevent moist interior air from coming in contact with the fenestration assembly.
*Kenneth M. Itle, AIA, of the Wiss, Janney, Elstner Associates (WJE) Northbrook office contributed to this article.
The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect those of The Construction Specifier or CSI.
Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at dslaton@wje.com.
David S. Patterson, AIA, is an architect and senior principal with WJE’s office in Princeton, New Jersey. He specializes in investigation and repair of the building envelope. He can be reached at dpatterson@wje.com.
