Mechanical parts of the drain assembly
High drain perimeters guards, mesh covers, flow control devices, and retrofit drain inserts are examples of mechanical parts that can obstruct drainage. When used as intended, they will enhance the roof’s drainage. However, flow control with no overflow drainage or drain screens/membrane clamping rings not having clear drainage can hold back water to the point that things turn ugly. In worst case scenarios, excessive water impacts the roof’s performance and safety.
Retrofit options
There are retrofit options available to improve the roofs drainage after the roof has been installed.
Maintenance
Ongoing maintenance is required to keep the drains clear of debris. Any building operator on a regular basis can check the roof drainage by removing leaves, dirt, and garbage from around the roof drain surface. Ballast guards and drain screens prevent debris from entering the drainpipes themselves, but debris can build up around the guards, and if not cleared regularly, can cause blockage. This can be outsourced to a contractor, and if modifications need to be completed which the contractor can implement.
Prevent or remove mechanical obstructions
There are drain fittings that can be installed on the inside of the drainpipes, which are an option when installing new insert drains where interior plumbing is not accessible. However, these reduce the flow rate from the original drain due to the reduction in plumbing pipe diameter and may result in the same roof being under designed for the hydraulic load required by the code. These devices can be avoided by accessing the drains from the underside and installing fittings on the exterior side of the pipes.
While new buildings require flow controls, these devices should only be installed if the roof was designed for them, including overflow drains. On the same note, they should not be removed if they are already incorporated into the roof system, as the increased flow rate can overwhelm the municipal sewers.
Drain relocation
As mentioned, existing drains set at high points of the structural deck can cause standing water. Relocating the drains to the low points of the roof deck will promote drainage. This would require plumbing repairs and additional or repositioning of the drainpipes, and localized repairs to the entire roof assembly.
Adding drains or scuppers
Additional drains can be added to the roof area and, if feasible, new drainpipes can connect into the existing pipes. Again, plumbing repairs by a professional would be required. Note that installing extra drains beyond the original hydraulic load capacity should not be completed unless all the plumbing lines to the sewers are checked to be able to take the increased load. If not, then the interior plumbing pipes can burst and/or backup into the building.
Scupper drains can be installed along the exterior perimeter of the roof and used as overflow scuppers for emergencies, or at roof level to act as a consistent drainage outlet. Downspout connections from scupper drains can be either connected directly to storm drains or over splash pads, depending on local by-laws and the existing site drainage.
Add sloped infill
A slope can be integrated during construction of the roof or as surface retrofits. Lightweight concrete with built-in sloped insulation can be installed during a roof retrofit before the new roof membrane is installed. This can remain intact in a single building over many roof membrane replacement projects as the concrete will protect the insulation from deterioration.
