By Stefan Nespoli, P.Eng., BSS and Shawna Smigelski, P.Eng., BSS
Wood-framed structures in Canada have been increasing in quantity and complexity as building codes have been updated to permit taller wood-framed structures. Wood-framed construction is now common for both townhomes and midrise buildings, many of which offer balconies and terraces for resident enjoyment.
A balcony is an outdoor usable space that does not have indoor occupied space below or access to the ground. Wood-framed balconies can be constructed as cantilevered structures (Figure 1) or simply supported, for example, framing joists connected to a ledger board at the building face, and columns, beams, or other supports provided at the front edge.
A terrace is an outdoor usable space that has indoor occupied space below. Terraces are typically simply supported by walls on all sides and therefore present lower structural risk; however, there is higher risk of damage to the building interior resulting from leaks. In both cases, surfaces are typically sloped to drain water off the front edge or to a drain.
Wood-framed balconies and terraces can be durable and long lasting; however, exposure to precipitation, especially rain combined with snow melt, presents challenges in design, construction, and maintenance. Wood-framed structural building components are susceptible to moisture and must be protected to reduce risk of rot, mould, and structural failure. Since this article focuses on waterproofing systems, balconies will be referred to, however, this topic also applies to terraces as well.
Designers and builders commonly rely on sheet waterproofing membranes to provide waterproofing protection (Figure 2). In these systems, the primary risk areas for water ingress are at penetrations and terminations. At penetrations, such as a top-mounted balcony guard baseplates, water ingress can cause wood rot compromising guard anchors, creating unsafe conditions and structural concerns. At terminations, such as upturns at the building face or below an access door, water ingress can lead to wood rot, structural issues, and leaks to the building interior.
There are also common issues with water ponding, negative slope, and missing or minimal upturns below balcony door thresholds, increasing the risk of water ingress. Since wood-framed balcony structural systems are typically concealed from easy visual inspection by architectural details, such as soffit materials on the underside, water leaks can progress significantly before they are detected, which presents a risk to public safety.
Identifying and understanding these risk areas is critical to developing and constructing durable wood-framed balconies and terraces. Canadian Standards Association (CSA), S478:19 Durability in Buildings, defines durability as “the ability of a building or building element to perform its functions to the required level of performance for its design service life in its structure environment under the influence of environmental actions.”1 It is reasonably assumed by building owners that the wood framing members provided with protective systems are intended to serve the life of the building, just as they would expect of their walls studs or roof trusses. However, achieving this service life in wood-framed balconies and terraces requires rigor in design, construction, and maintenance of these risk areas.
Penetrations at horizontal surfaces
Penetrations through sheet waterproofing membranes present a high risk for water ingress leading to wood rot. Where possible, penetrations should be avoided altogether or elevated off horizontal surfaces where water collection is expected. Where penetrations are required, durable seals must be provided since the waterproofing membrane is not self-sealing.
