< Previous20 Pushing the Envelope Canada • Fall 2025 FEATURE erected on the building”. Fly-by curtain wall parapets have been used with both construction methods, but unitized curtain walls offer more flexibility in their design from conveniently located interlocking components such as the “chicken-head” at the stack sill. CURTAIN WALL ANCHORAGE AND DIFFERENTIAL MOVEMENT A curtain wall system must transfer both the gravity loads (e.g., self-weight) and the lateral loads (e.g., wind loads) back to the build- ing superstructure, typically via anchorage at building floor slabs. They must also accommodate in-service building movements such as vertical slab deflections due to live load, horizontal Interstory drift, and thermal movements of the curtain wall itself. Anchors typically consist of “F” and “T” clips when the system spans floor-to- floor or “J” hooks or angles at intermediate floors where the curtain wall is supported outboard of the slab edge. In the case of the fly-by curtain wall, there is no floor slab at the top of the parapet, therefore the structural support system at the roof line must be designed to support the parapet’s top edge. Options include either: • An independent outrigger structure (for gravity, lateral, or both) which supports the top of the parapet (Figure 6), or • An internal structural reinforcing element embedded within the mullions which is designed to cantilever from the roof level (Fig- ure 7). WATER MANAGEMENT FEATURES A curtain wall normally faces in one direction, where the outer portion includes water management features (e.g., glazing pocket and weeps). The interior-facing side of curtain walls are not de- signed to be watertight. Yet, in a fly-by curtain wall, the normally-in- terior-facing side is now exposed to the outdoors. Addressing this requires either incorporating water management features (i.e., flashing within unitized curtain wall stack joints) or preventing water from reaching the system (i.e., creating a barrier). Systems which drain and manage water are generally more reliable than barrier systems – for all building envelope systems! DESIGN CONCEPT The fly-by curtain wall parapet approach which addresses all of the design considerations above is one which uses a unitized curtain wall system with an independent outrigger (Figure 5). De- signs which include stick-built curtain walls or cantilevered support systems are possible with select manufacturers, but they are more difficult to resolve the structural loads and to make watertight. Consider the following features when designing a fly-by curtain wall parapet: • Provide a continuous curb around the roof edge, covered by the roofing membrane base flashing, and sloped towards the roof. • Locate curtain wall stack joints at least 8 in. above the walking surface, and above the perimeter curb. • Provide membrane flashing (over a continuous support) bridg- ing between the curtain wall and roofing membrane to com- plete the building’s water barrier. For unitized systems, turn the membrane flashing up the back of the chicken head. • Protect membrane flashing with metal counterflashing. Figure 4: A stick-built curtain wall sequence. Figure 5: A unitized curtain wall sequence.Figure 6: An outrigger support concept.Building Science Association of Ontario 21 FEATURE • Cover splice joints in the chicken head and horizontal mullion with elastomeric membrane (e.g., silicone sheet) to maintain watertightness. For details with a cantilever support, internal reinforcing inter- rupts the plane of membrane flashing and must be detailed like a penetration – with membrane flashing turning up each internal post a minimum of 8 in. and detailed with sealant. For details with stick-built curtain wall, the horizontal mullions are not interlocking, therefore the membrane flashing must cover the entirety of the horizontal mullion. To mimic a unitized curtain wall, consider disjointing the stick-built curtain wall into independ- ently supported upper and lower units (with a double horizontal mullion). TAKEAWAYS This introductory article illustrates an example design strategy to integrate a fly-by curtain wall parapet with the roof system. Each project’s design intent and constraints create unique challenges to overcome. Many manufacturers are also developing proprietary toolkits to accommodate this challenging detailing. Keep in mind the following tips next time you encounter a fly-by curtain wall parapet: • Disjoint the fly-by parapet from the curtain wall below. • Identify the wet/dry line and detail accordingly. • Outrigger options offer greater flexibility for fly-by elements. • Specify a first-in-place mockup. • Field quality control testing is critical. ■ Maria Raggousis consults on building enclosure design, rehabilitation, and investigation projects for owners, architects, and general contractors. Maria also specializes in thermal and hygrothermal analysis for both new design and existing building projects to develop performance-based solutions in predicting, mitigating, or reducing moisture-related damage to building enclosures. Sam Zalok is experienced in new building enclosure design and consulting, building enclosure leakage investigations, and building enclosure rehabilitation designs, including below grade waterproofing systems, masonry and flashing systems, and roofing systems. Sam’s specific specializations include new construction building enclosure consulting, roof replacement design, facade rehabilitation design, and plaza waterproofing design. Figure 7: A design reinforcing concept.Figure 8: A design concept with unitized curtain wall and outrigger support system.22 Pushing the Envelope Canada • Fall 2025 FEATURE I n new condominium and rental resi- dential buildings constructed with wood framing, balcony guards are often treated as finishing details, installed late in the construction process and rarely revisited until something goes wrong. Yet when post base connections fail, they don’t just compromise the guard; they com- promise resident safety, expose hidden structural vulnerabilities that can escalate rapidly and expensively, and undermine the confidence of residents and property managers alike. WATER AND ROT Wood-framed balconies are particular- ly susceptible to deterioration due to two key factors: movement and moisture. Un- like steel or concrete, wood expands and contracts more with seasonal changes in temperature and humidity. Guard posts that are anchored into the balcony wood framing must resist lateral loads from leaning, pushing, or sitting. When mois- ture infiltrates the framing, the structural integrity of these connections can degrade quickly, often without visible warning signs. The first line of defense against mois- ture ingress is proper waterproofing de- tailing. Unfortunately, this is often where things begin to unravel. Guard posts are frequently installed directly onto balcony top surfaces without curbs, gaskets, seal- ants, or integrated membrane protection. These omissions create direct pathways for water to enter the framing below. In some cases, membranes are installed be- fore guard bases are set, but no follow-up sealing occurs. Further, guard designs that include hollow steel or aluminum posts or sleeves can trap water inside, accelerating deterioration and channeling moisture downward into the wood substrate. These failures are rarely visible until wood rot is advanced. This is especially problematic because the wood framing in these balconies is not pressure-treated. Often located above conditioned living spaces, or exterior patio areas meant to be protected from above, the framing is designed to remain dry and is not equipped to handle moisture ex- posure. Once water enters, there are no provisions for drying, and deterioration be- gins silently. The current Ontario Building Code requires waterproofing membranes and flashing to prevent moisture ingress, but it does not provide explicit detailing requirements for pedestrian membranes over wood-framed balconies. As a result, performance depends heavily on product selection, detailing at transitions and inter- faces, builder execution, and inspection quality. STRUCTURAL MISSTEPS When moisture compromises the wood framing that guards are fastened into, guard connections become especially vul- nerable. Structural missteps are common and often hidden behind finishes, that present risk even if moisture has not en- tered. Guards are frequently fastened into only the rim board without adequate block- ing to resist code-specified applied loads. Fasteners such as drywall screws or under- sized wood screws are still encountered in the field, despite lacking the strength, cor- rosion resistance, and embedment depth needed for strength and long-term stabil- ity. Guards may also be mounted at odd angles, transferring force eccentrically and introducing rotational stresses that loosen connections over time. These vulnerabilities are not hypothet- ical – they are frequently discovered only after significant deterioration has occurred, often requiring both structural repairs and improvements to waterproofing detail- ing. Such issues are increasingly found in buildings between eight and ten years old, typically beyond the coverage of applicable new home warranties in Ontario. Because failures tend to surface outside of the war- ranty period, options for recovering repair costs from the builder are limited. CASE STUDY: A QUIET FAILURE IN WATERLOO, ONTARIO During a leak investigation of an eight- year-old wood-framed condominium in Waterloo, Ontario, visibly loose guard rails identified prompted further professional investigation. Fast-forward to removal of the waterproofing, the cause was immedi- ately clear: water infiltration at the base of the guard post had rotted the rim board entirely. The anchorage screws had lost their withdrawal and pullout resistance, and the railing was held in place by little more than friction. The root causes were threefold. First, there was no waterproofing membrane below the guard post base to prevent mois- ture ingress. Second, the connection lacked adequate blocking behind the rim board to support the guard post anchorage. Third, Guarding Against Failure: Hidden Vulnerabilities in Wood-Framed Balconies Damage shown from the case study in Waterloo, Ontario. Photos courtesy of Shelby Hyland. By Shelby Hyland and Stefan Nespoli, Edison Engineers Inc.Building Science Association of Ontario 23 FEATURE there had been no regular inspections or sealant renewal at the base plate. This wasn’t a 30-year-old building; it was less than eight years from occupancy. This fail- ure was predictable and preventable. An expansion of the review uncovered similar deterioration, at various degrees of progression, at a majority of balconies at the property. MANAGING WOOD-FRAMED BALCONIES Even with proper detailing and design, wood balconies and associated guards are subject to wear. To help identify early signs of failure and maintain balcony safety, Building Owners and Property Managers can incorporate the following into their an- nual inspection routines: • Check for lateral movement or wobble in guard rails (especially if this increases over time) • Inspect sealants at guard post base plates and transitions • Look for rust, staining, or soft wood at post bases • Check for water stains around post bases on soffits below • Verify that drainage pathways around posts are clear • Confirm visual access to fasteners and anchorage points at guard post bases • Ensure sealants are in good condition and reapply as needed • Document and photograph any signs of deterioration for follow-up • Retain a professional engineer if any concerns arise, whether localized or widespread, and every five years to assess structural integrity and recom- mend appropriate remediation. By recognizing and addressing these vulnerabilities early, you can protect owners and their residents, reduce overall repair costs and preserve the long-term perform- ance of their buildings. When these ele- ments come together, they not only prevent failure, but they also build safer, more resili- ent communities for years to come. ■ Shelby Hyland, P.Eng., is a Restoration Project Manager at Ed- ison Engineers Inc., where she applies her background in structural design to restoration projects for residential and condominium cli- ents across Southwestern Ontario. Stefan Nespoli, P.Eng., BSS, is a Principal and Regional Lead at Edison Engineers Inc., where he leads technical teams delivering performance audits, reserve fund studies, and repair design projects for condominium and residential clients across Southwestern Ontario and the Greater Toronto Area. Water infiltration at the base of a guard post, rotted through.24 Pushing the Envelope Canada • Fall 2025 MEMBERSHIP OPENS THE DOOR TO SO MUCH MORE! MORE LEARNING Conferences, Technical Forums, and Field Trips. MORE PEOPLE Architect’s, Engineers, Educator’s, Manufacturers and Contractors. MORE OPPORTUNITIES Construct Canada, Dinner Meetings and Social Events. Join Today! bsao.caMembership opens the door to so much more. More learning: Conferences, technical forums, and field trips. More people: architects, engineers, educators, manufacturers, and contractors. More opportunities: Construct Canada, dinner meetings, and social events. In 2025 OBEC rebranded to the Building Science Association of Ontario (BSAO) with the mission to advocate for building science and provide quality education and forums for collaboration for members to network and increase their technical knowledge. Our vision is to ensure we are the gold standard in building science education and professional networking. 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