• 26 th May, 2020

Consequences of incorrectly installing roof drains with waterproofing membranes

Concrete has been highly renowned as one of the best materials used for roof construction and has been adapted in most modern commercial and residential building construction. However, the concrete flat roof alone will not guarantee the prevention of leakage issues. The water on the roof will stagnate over time and likely leak into the structural slab, which will in turn cause roof leakage. On a roof during construction, there are various points of susceptibility such as roof drains, gutters, downspouts, and scuppers. It is critical that these points and the construction material are given the utmost importance during construction to ensure that there is no leakage on the roof. However, we must not ignore the installation of the waterproofing membrane associated with the roof drains.

The waterproofing of the roof is the formation of an impermeable barrier between structural slab and other layers on the roof. This ensures that water does not penetrate the roof slab and the structural integrity of the building is maintained. The waterproofing is completed using waterproofing membrane, which is a layer of watertight material that is laid onto a surface to prevent water leaks or damage. Waterproofing membranes generally consist of pre-formed sheets or liquid applied membranes. They can be adhered or installed above the structural slab to prevent water penetration. Roof failure is usually caused from water related issues. Hence, showing the great importance of waterproofing to keep the roof protected.

Improper applied waterproofing is equally bad as no waterproofing at all. The necessity of the waterproofing membrane is continuous throughout the entire roof, but that continuity breaks at the drains. This problem can be avoided if you have a provision of properly installing the waterproofing membrane to the roof drains.

Saudi Cast’s range of roof drain products (FD-4050, FD-4060, FD-4160, FD-4080, FD-4010, FD-4020, and FD-4100) come with a waterproofing clamping device that ensures that the water leaked through the different layers halts at the membrane and flows towards the drains. Saudi Cast recommends following installation steps of the waterproofing membrane associated to roof drains:

1. Slope the concrete screed layer towards drain:

When the surface is flat, the water will seep through the top layers then stop and form puddles on the waterproofing membrane. This can accelerate the degradation of the existing waterproofing materials used. Therefore, roof designers recommend creating a slope towards the drain by spreading the concrete screed (light form) on the flat roof to have the water flow gradually towards the roof outlets. Place the waterproofing membrane along this slope to direct the seeped water towards the roof drains and in turn into the drainage pipes.


2. Properly install waterproofing membrane and fix it with the drain:

This is one of the most important steps to make roofs watertight. Start applying the waterproofing membrane on the roof drain first then work your way around the rest of the roof (as per manufacturer’s instructions). Place the membrane in between the roof drain body and clamp and securely fastened it using the bolt. This properly ensures the continuity of the membrane on the roof. The membrane must lay flat and contour the body opening. Next, install the waterproofing membrane on rest of the roof with proper overlapping to join adjacent membranes; it must then be elevated up to the height of the conjoining roof walls as per the manufacturer’s recommendation. Hydro tests are mandatory before installing the next layer.


Nevertheless, even if all of these steps are followed correctly, roof leakage still may occur, which will damage the waterproofing membrane itself or disturb the continuity of water flow. The reason this could still happen are as follows:

a. Open penetrations

Open penetration to roofs occur at the drains, vents pipes, HVAC units, gas lines and other systems that come through the roof membrane. These penetrations can be sealed using Saudi Cast’s drains that come with proper pipe fixation arrangement, vent stack flashing sleeves FD-8030, and parapet sleeve FD-8050.

b. Damaged roof flashings

Roof flashings are the metal pieces installed on the roof edges. When a flashing has not been installed correctly or when a metal flashing has aged, it can cause water to seep into the roof slab and damage it. Therefore, it is very important to install the roof flashings properly and maintain it regularly.

c. Debris

Buildup of debris can trap water on the roof for a long period and allow it to seep in an excessive amount of water by capillary action, which will damage the waterproofing membrane itself. Hence, it is important to keep the roof clear to permit water to run off rapidly.

Roof leakage problems associated with waterproofing membranes in connection with roof drains can be avoided with the use of Saudi Cast’s roof drain, which comes with a proper waterproofing fixation mechanism. Ensuring waterproofing membrane continuity if roof drains are installed as per Saudi Cast’s recommendations.