Balconies offer access to the outdoors, providing fresh air, sunlight, and views, while enhancing a home’s value and appeal. However, as they age, these features demand structural repair and upkeep to remain safe and inviting.

Most balconies on taller buildings are made of reinforced concrete construction, while those on low-rise structures typically feature wood framing. Both systems can undergo structural deterioration when exposed to moisture and air over time.

Concrete balconies most often suffer from corrosion of their embedded reinforcing steel, while wood-framed balconies usually deteriorate due to rot. Other causes of deterioration can include construction deficiencies and poor workmanship, overloading of the structure, inadequate design, poor detailing, or the use of poor-quality materials during the construction phase of the building.

Steel framing

Steel framing with concrete encasement—common in the 1950s and ‘60s—may resemble traditional reinforced concrete slabs, but is often more susceptible to certain types of failure. Concrete delaminations or spalls may indicate deeper problems than in a standard reinforced concrete design.

Reinforced concrete

Reinforced concrete balconies make up the majority of mid-to-high-rise buildings constructed from the 1960s to today. Reinforced concrete is very durable due to its high alkalinity, moisture tolerance, and lower permeability. Provided the concrete is maintained in a high alkaline environment, the reinforcing steel will not corrode.

However, concrete loses its protective properties if its alkalinity is lowered due to external factors such as carbonation, which attacks the protective layer and initiates corrosion.

Carbonation is the result of a chemical reaction between carbon dioxide (CO2) in the air and the calcium hydroxide in the cement. The rate of carbonation and its impact on the corrosion of the embedded reinforcing steel depends on the quality of the concrete and the depth of concrete cover over the reinforcing steel.

Typically, the first visible sign of deterioration in concrete is the appearance of cracking, followed by spalling in the areas where more progressive reinforcing steel corrosion has occurred. The spalling of the concrete will often expose the reinforcing steel—and once the corrosion process begins, it will continue at an accelerated rate. Spalled pieces of concrete may result in falling hazards to people below.

Waterproofing membranes are often added to concrete balconies to prevent or reduce concrete deterioration and the risks of water infiltration. However, many concrete balconies—including newer builds—were originally constructed without protective membranes.

Precast or masonry balustrades

Many older balconies have exterior walls or balustrades rather than the modern glass and aluminum railings. These include precast concrete balustrades that may be secured to the balcony slabs with embedded steel anchors. Corrosion of the balustrades or anchors can result in safety issues that require attention. Masonry and precast balustrades are often removed completely and replaced with more modern railings. However, this is a fairly major undertaking that is more expensive than the typical railing replacement.

Wood framing

Wood-framed balconies are typically constructed of engineered wood joists that extend from within the building, cantilevering beyond the facade. The tops of the joists may be secured with plywood sheathing and are often protected with a thin sheet membrane. Unlike traditional concrete balconies, wood balconies are protected with a roofing membrane complete with proper “tie-in” to the wall control layers. Where water is allowed to penetrate to the structural wood elements, the load carrying capacity of the balconies can be reduced and shoring may be required for safety. Wood can deteriorate rapidly when exposed to water, and some engineered wood products rot much quicker than traditional lumber.

The protective membrane is susceptible to damage from sharp objects. Since dragging chairs can damage the surface, padded furniture feet are recommended.
The weight of objects placed on a balcony should also be considered. Very heavy objects, such as hot tubs or deep planter boxes, should not be placed on balconies without first confirming that the structure can support the load, typically through an engineering review.

Airflow around the balcony structure allows the wood to dry out, reducing the opportunity for rot. The membrane system, when working, prevents the wood from getting wet. However, if there are any imperfections in the membrane, such as pinholes, water can seep through to the wood. The membrane can actually prevent drying and contribute to wood rot.

As such, it is important to keep the membrane in 100 per cent condition, especially as the system ages. Otherwise, the medium-sized job of membrane replacement can expand into the much larger job of full balcony system replacement.

Balcony railings

Current designs typically include aluminum pickets, aluminum panels, or glass with aluminum posts. Issues with spontaneous glass breakage have been a concern in the 2000s, resulting in code changes and some new buildings requiring full replacement at that time.

Like other components, corrosion may occur at the railings or the material they are fastened to. In both scenarios, the railings may not be strong enough if someone leans on them.

It’s worth noting that building code requirements for railings have evolved over time. While older systems may not meet current standards, they may be grandfathered—depending on the jurisdiction— if they were compliant at the time of construction.

Owners should be aware of this as they may have railings that are less safe, particularly in the “climability” of the railings, which can be of additional concern to those with children or pets.

Balcony structural repair projects

Noise and loss of outdoor space are primary considerations for balcony repair projects. Although it would be more convenient to have the work complete in the winter when the balcony is not used, there are technical reasons that the work must be completed in warmer weather.

For example, concrete repair materials and liquid waterproofing systems generally need to be installed in above-freezing temperatures (above 10C is ideal). The noise from concrete chipping can be disturbing, even in areas far from the work zone, as the sound travels through the building structure. It is best to leave the unit when concrete chipping is happening nearby.

Balconies offer a great connection to the natural world and are a wonderful asset to any home. Yet over time, exposure to the elements and defects can lead to gradual deterioration. With foresight, homeowners can avoid costly repairs and, instead, preserve these spaces as an easy retreat into the outdoors.

Jack Albert, P.Eng., is a Principal with RJC Engineers. Jack is a member of the Ontario Building Envelope Council, IIBEC, and is a LEED Accredited Professional. Over the past two decades, Jack has completed many projects involving building envelope repairs as well as studies and audits.