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The most common and high-risk penetration at horizontal surfaces with high exposure are balcony guard baseplate anchors. Guards are an integral safety component of any balcony or terrace. The building code also specifies loading and dimensional requirements for guards. Guards are commonly top mounted on both concrete and wood balconies. The guard is structurally connected to the balcony with vertical anchors. In wood balconies, the anchor holes penetrate the vinyl waterproofing membrane and often rely on direct pull-out resistance where water penetration can quickly reduce anchor strength. Anchor penetrations must be provided with a durable watertight seal to maintain guard safety (Figures 3 and Figure 4).
In addition, top-mounted guard baseplate securement methods often create depressions around the baseplate that attract water and thereby increase the severity and duration of moisture exposure. Defects under these conditions cause accelerated deterioration. During installation, guard baseplate anchors are fastened through the baseplate, waterproofing, wood sheathing, and into the structural wood blocking. Achieving the required torque for structural securement commonly compresses the waterproofing and wood sheathing, which creates a depression and allows water to collect around the baseplate (Figures 5 and Figure 6).
This risk is commonly addressed through perimeter sealant around the baseplate, sealant within the anchor holes, or a butyl gasket below the baseplate. These approaches can be combined for added redundancy.
Baseplate perimeter sealant
Installing sealant around the perimeter of the top-mounted baseplate is a simple but ineffective solution to protect penetrations. Relying on sealant is risky due to increased variables including proper material selection, compatibility, surface preparation, workmanship, and maintenance. De-bonded or damaged perimeter sealant is common and inevitable since the service life of the sealant is 10 to 15 years at best, compared to more than 20 to 30 years for the waterproofing and guards. This presents major durability concerns, even as something as a small imperfection in the seal presents a source for water entry (Figure 7).
In some cases, the perimeter sealant is provided with a gap, or weep hole, at the front edge to allow any water entering the guard post to drain out. Drain holes are provided at guard post bases to drain water entering the guard assembly through joints, which is a direct bypass of the perimeter sealant and contributes to water entering the anchor penetrations. There are clear risks with providing a gap in the baseplate perimeter sealant, especially when considering the baseplates may be set in depressions created when the guard is anchored. Even though the weep hole is on the positively sloped side of the balcony, it now sits lower and is an easy source for water entry.
Further, the detailing at the balcony drip edge flashing may prevent drainage, and instead direct water back toward the weep hole (Figure 8). This is reviewed in detail later.
Butyl gasket below the baseplate
A butyl gasket or pad may also be placed below the guard baseplate to provide a seal to protect the anchor penetrations (Figure 9). However, when the pads are either not fully engaged (Figure 10) or skewed, the anchors are vulnerable to water entry. In addition, if adhesive pads are used but the release film is not removed, the seal will be compromised.
Anchor penetrations
To provide a seal directly at anchor points, the anchor pilot holes are filled with sealant prior to installing the fasteners (Figure 11). In general, this approach is effective. However, there is still a risk of water entry as the sealant ages and fails, alongside poor levels of protection if not installed correctly. Since it is concealed, the integrity of the seal cannot be confirmed on installation, and regular inspection or maintenance of the sealant itself is not feasible. During investigative reviews of new construction, there may be areas with no protection at the penetrations at all (Figure 12).
Lag bolt versus through bolt anchors
Lag bolts are commonly used to secure guard baseplates because they are easy to install and do not require access to the balcony underside. This is common in new construction, where balcony waterproofing and soffits have been installed by the time the guard installation crews arrive on site.
Using through-bolt anchors in lieu of lag bolts provides additional redundancy in maintaining guard securement. A threaded rod (or carriage bolt) is installed from the baseplate to the underside of the structural wood blocking, terminating with a washer or plate and nut. This changes the structural connection from relying on pull-out resistance of the lag bolt to the bearing capacity of the washer or plate and nut on the underside of the wood blocking. Since the risk is that water will enter from the top side of the balcony and deterioration will inevitably occur, lag bolts are much more susceptible to loss of structural capacity due to wood rot and deterioration within the anchor penetration.
Using through-bolts reduces the risk of total failure of the guard as the bearing capacity is dependent on the surface farthest away from the water entry point. Where guard baseplates align with framing joists, lag bolts can be used in combination with through-bolts.
