Balcony Waterproofing

Does your firm build or design multi-family construction projects? If so, this type of construction is often one of the most litigious areas of commercial construction today because most multi-family units have balconies where water intrusion often occurs. When structures have balconies, there is a greater chance for water to penetrate the building enclosure, requiring you to get several layers of flashing details correct. Unfortunately, tragic results can ensue when water intrusion is not properly flashed and protected.

Luckily, there are resources available to help make sure you are doing the job right.



Building code requirements for balconies and exterior low‐sloped structures (below a 2‐in. rise in 12 in. of run; 2:12) fall under Chapter 15 of the International Building Code. However, a slope of this extent would not be comfortable for daily use, thus often the slope for the balcony is reduced to the minimum slope allowed by code of 1/4‐in. rise in 12 in. of horizontal run. This is also nearly equal to the maximum slope allowed for landings at exterior opening doors of 2 percent. Often, though, the slope is created with a topping over the structural element that leaves the designer with a decision as to how to make the control layers integral within the vertical opaque wall system with the horizontal balcony. For this piece, we will examine the common wood framed balcony assembly with a lightweight concrete topping.


  • Scupper and overflow
  • Drain
  • Handrail termination/attachment at the horizontal deck surface
  • Control joints
  • Expansion joints
  • Drain mat above the waterproofing layer and below the concrete topping
  • Parapet wall on the outer edge or open slab edge
  • T‐bar edge system incorporating the slab waterproofing membrane
  • Integration with the water‐resistant barrier (WRB) of the vertical wall with the horizontal flashing system of the balcony
  • Termination of the wall cladding above the finished topping of the balcony with adequate clearance as recommended by the manufacturer
  • Sealing of the exterior entry door to the balcony
  • Additional topping coatings on the concrete, which requires careful consideration in its water permeance and resistance from hydrostatic pressures from below if the waterproofing layer is also included on the sheathing below a coating
  • Paver or a tile finish system that is elevated on pedestals


Step 1: Location of the Waterproofing Layer. Determining how one is going to waterproof the system is a critical decision that should be decided prior to moving forward with other detail considerations. []

Step 2: Waterproofing Details to Consider. No matter which method is chosen, the key principal to consider within the design is to be sure to give water a chance to get out of the assembly.

Step 3: Supplemental Details. Once the system is determined and the waterproofing elements and approach have been designed, one should consider other elements and details that are often affected by a balcony placement.

Step 4: Final Considerations. Coordination of the architectural design intent and structural requirements of the loads and reactions is an integral part of the balcony design.


As an exposed, external structure, a balcony also requires thorough and well planned maintenance. This includes checking for stability and overall condition and integrity, in addition to many specific issues. You should inspect any brick for mortar integrity, grout condition and misalignment; wood parts should condition for deficiencies such as dry rot, termites, instability, worn edges, cracks, holes, and splintering. Ensure that any metal surfaces do not show signs of discoloration, cracking, rust, peeling or splitting.

For any stucco, check for signs of chipping, flaking, efflorescence, and cracks. Hardware around the structure should be inspected as well for condition.

As far as the structure goes, check the footings/foundation and the fire escapes. They must maintain their overall function, as per local building and fire codes, and the condition of access points must still be met.

Most importantly for the purposes of waterproofing, you will want to inspect the decking waterproofing system for deficiencies such as cuts, tears, blisters, as well as ensuing that any and all water flow is away from the building.

A full check-list for balcony inspection, as well as a plethora of other forms of preventative maintenance, can be found in John C. Maciha’s book Preventive Maintenance for Multi-Family Housing.

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