If failures arise in the bed of sealant, repair or replacement becomes much more difficult. Repairing or replacing a perimeter caulk joint is feasible, however, when a flashing is introduced, the bed of sealant that the flashing rests on is not a serviceable joint.

Maintainability is also a factor that should be considered with the design of a sill condition. Pre-installed on the verticals, which means gaining access to seal the fastener or the perimeter of the clip would be extremely limited and would most likely require a blind seal. These penetrations are often made for fastening “F” or “T” clips that attach the curtain wall verticals to the substrate. When a sill flashing is required to be used, an upturn leg as shown on the detail above would not provide the benefit of additional waterproofing support as intended due to the following:Ī) Curtain wall systems, or any other systems that do not have an integral sill flashing design, will require penetrations to be made with the fasteners through the sill flashing. While this is an option, it requires additional steps which equates to more cost.

In a case such as this, a sill flashing could serve the function of marrying the waterproofing to the curtain wall system by setting the flashing into a bed of sealant that is compatible with the membrane and then caulking the curtain wall to the flashing, allowing compatibility on both sides of the flashing. An example would be if a waterproofing membrane was being used on the substrate that was not compatible with the perimeter caulking. In some cases a sill flashing piece may be required due to the substrate the system is attaching to. If a system does not have a sill flashing extrusion that is provided by the system manufacturer, then the sill flashing is not integral to the functionality of the system, and additional testing may be required. There are now two joints that become critical to maintain the system’s waterproofing integrity: the perimeter joint, as well as the bed of sealant that the sill flashing is set on to. For curtain wall systems that do not include a sill flashing extrusion as part of the system, a detail such as this can pose the following problems:

Stone curtain wall system