Maintenance and Repairs

July 4, 2025 Published by Golden Horseshoe Chapter - By Brad Gascoigne, Griffen Brunk

Built with Wood, Bound for Trouble? What the Past Can Teach Us About Ontario’s MURBs

From the Volume 24, Summer 2025 issue of the CCI GHC Condo News Magazine

Wood-frame construction has long been a staple in North American residential and light commercial development, valued for its affordability, speed, and sustainable qualities. In low-rise buildings, this construction method has been refined to a high degree of efficiency, performance, and reliability.

Wood-frame construction has long been a staple in North American residential and light commercial development, valued for its affordability, speed, and sustainable qualities. In low-rise buildings, this construction method has been refined to a high degree of efficiency, performance, and reliability.

Following changes to the Ontario Building Code in 2015 that allowed woodframe construction for buildings up to six stories and with a push to increase density and affordability in housing, wood framing is increasingly being used in multi-unit residential buildings (MURBs). Adapting light wood framing to larger, multi-unit residential buildings brings some additional challenges. Chief among them is wood’s susceptibility to moisture damage.

Over the past couple of years, we have started to encounter a worrying trend: many recently constructed, wood-framed MURBs are exhibiting significant structural deterioration within just a decade of being built, primarily due to water infiltration through the building envelope. By the time the deterioration becomes apparent, extensive and costly repairs are often required. The root causes are usually tied to poorly designed and executed building envelope details. As sustainable as wood-framed construction is, there is nothing ‘sustainable’ about needing structural rehabilitation after only 10 years.

While conventional concrete or steel-framed MURBs certainly aren’t immune to these detailing problems – they too have building envelope deficiencies - they don’t have the inherent durability issue that wood-framed buildings face: wood rots. A leak in a concrete building will not compromise the structural integrity of that building, as it will in a wood building.

This is not new territory. Those of us with some grey hairs may remember British Columbia’s infamous "leaky condo crisis" from the late 1980s to the early 2000s. This ‘crisis’ affected thousands of wood-framed townhomes and condos. Many of these buildings began leaking shortly after construction, often going unnoticed until water had already irreparably damaged building envelope and structural components, leading to widespread rot - requiring significant restoration. The result was billions of dollars in damage. Homeowners and condo corporations bore the financial burden, requiring government intervention at the height of the crisis to provide large interest-free loans to fund critical repairs.

So what went wrong then?

The architectural style of the time borrowed heavily from Mediterranean and Californian influences, incorporating features such as face-sealed stucco systems (EIFS), minimal or no eaves or overhangs, and complex envelope interface geometries. While just fine for dry climates, these details weren’t really adapted to perform in the Pacific Northwest, where it rains. A lot.

EIFS, which are synthetic stucco systems, became popular in North America during the 1970s and ’80s. They initially relied on face-sealed assemblies, imported from dryer climates, intended to stop water at the outer surface of the assembly. However, once water penetrated the assembly, it had no pathway to drain or escape, leading to trapped moisture, decay, and rot. The absence of eaves reduced shelter and protection, and the complex cladding interface geometries, intended to add architectural interest, further complicated the building envelope details.

During remediation efforts in B.C., poor workmanship and poor detailing were found to be widespread. The design choices amplified the problems caused by rushed construction. The provincial commission also found there to be a lack of awareness around the principles of building enclosure design and inadequate inspection during construction.

Back to Ontario in 2025. If you look closely at many new wood-framed MURBs in Ontario today, you might notice some similar trends: flat roofs with minimal overhangs, diverse cladding materials, and complicated envelope interface details, especially around balconies. The industry has at least learned the lesson of redundancy and has moved toward drained cladding assemblies for better water management. Drained assemblies that allow water to penetrate behind the cladding, to be managed by underlying water-resistive barriers (WRBs) and finally to be safely discharged, are now standard in modern construction. But like most things, the devil is in the (envelope) details. We often see that the critical building envelope details on these MURBs are still poorly considered and very susceptible to construction defects.

There is also a tendency to use envelope details and construction materials on wood-framed MURBs that might be more appropriate on single-family homes. The common culprits are exposed, single-ply balcony membranes (rather than more robust, multi-ply, protected assemblies) and housewraps used as water-resistive barriers (WRBs) behind cladding systems (rather than more robust, fully-bonded WRB options). Perhaps because single-family homes and wood-framed MURBs are superficially similar, the thought is that the same construction trades, building materials and envelope details can be readily applied to both? Unfortunately, envelope deficiencies on a 4+ storey MURB are much less forgiving than on a single-family home.

Another factor is that wood isn’t really wood anymore. Wood-framed construction utilizes a lot of engineered wood products, such as oriented strand board (OSB), laminated veneer lumber (LVL) and others. These products make very efficient use of materials, but they can be even less moisture tolerant than conventional board lumber.

That brings us to the final issue: a serious skilled labour shortage. Fewer young people are entering the trades, and many seasoned professionals are retiring without successors. As a result, construction crews are smaller, work is rushed, and the overall skill level in the labour force is declining. This leads directly to an increased risk of deficient envelope detailing.

If governments are going to meet their housing targets over the coming years, many more MURBs will need to be built, and a significant number of them will be wood-framed. If we are going to avoid the pitfalls of the past, as an industry, we need to carefully consider how we are designing and detailing this generation of wood-framed MURBs.

For condominium corporations and owners dealing with MURBs that are already built, by the time serious damage manifests, leakage may have been festering for years, and buildings may be beyond the coverage of the 2-year or even the 7-year Tarion warranties. So what can owners of newer wood-framed MURBs do to mitigate risks and hopefully avoid costly future repairs?

During the Performance Audit phase, ensure the auditor conducts a thorough review of the building envelope, particularly in high-risk areas: cladding interfaces, balconies, and flashing details. Even if no problems are apparent, localized destructive review can reveal early signs of failure or concealed deficiencies within the Tarion warranty timelines.

Plan for regular reviews and assessments by qualified professionals. Assessments can help evaluate the performance of cladding and water management systems and can detect early signs of deterioration before they develop into major, costly repairs.

Finally, treat even small signs of leakage seriously. Minor staining can be an indication of a deeper issue. Avoid cosmetic “band-aid” fixes, consult a professional, and address the root causes.

“An ounce of prevention is worth a pound of cure” holds especially true for wood MURBs.

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Brad Gascoigne, B.Arch.Sc., BSS is the Principal, Building Science at Brown & Beattie Ltd., a firm that is dedicated to providing clear and sensible building improvement, maintenance and planning advise. Brad holds a Bachelor of Architectural Science in Building Science from Ryerson University and a Building Science Specialist (BSS) designation.

Griffen Brunk, P.Eng. is a Project Engineer at Brown & Beattie Ltd. He holds a Bachelor of Applied Science in Civil Engineering from the University of Waterloo and is registered with Professional Engineers Ontario (PEO).