top of page


  • Tom Stratton

A step-by-step guide to waterproofing your roof

A step-by-step guide to waterproofing your roof


There are many reasons for a leaky roof, but poor or inadequate waterproofing tops the list. And if the city or area you live in is prone to heavy rainfalls, waterproofing the roof is imperative to prevent long-term structural damage. This guide will cover everything from the importance of waterproofing to the materials required and the step-by-step process involved. 

What is waterproofing?

Roof waterproofing adds that extra layer of protection to ensure no water enters your walls through the roof, thus protecting your structure from water damage and rot. Waterproofing is one of the most critical steps in the roof installation process.

Why is it important to waterproof the roof?

Before we look at the technical aspects, let’s understand why waterproofing is integral to roof maintenance.

Reduces cost of repair

Waterproofing your roof will ensure that, in the long run, you save a lot on the costs of repair and maintenance. Any roof or roofing material will eventually outlive its life span, but protecting it from the harsh elements of nature will prolong the roof’s life. 

Maintains the structural durability of your home

If you have a leaky roof, water will eventually seep into the walls of your home and gradually erode the beams and structures supporting your home. Roof waterproofing is essential to maintain the structural durability of your home. 

Maintains the energy efficiency of your home

Waterproofing, when combined with a coating of UV membrane, will act as a protective layer against the sun’s harsh rays, thereby maintaining the temperature in your home, which leads to a lower electricity bill. 

 Prevents growth of mold and mildew

A damp roof can cause mold and moss to grow not just on the roof but also on the wet walls of the interior of your home. Stained roofs and interiors do not just indicate neglect, but long-term dampness in the home can lead to potential health issues for you and your family. 

Prevents visible water stains

Water stains on the walls and ceilings are an eyesore, and if you are in the market to sell your property, it can substantially bring down the property cost. Waterproofing will ensure that your home or property remains beautiful inside and outside.

Materials used in waterproofing

There are many types of waterproofing materials in the market. Selecting the suitable material for your roof will depend on the external temperatures, the level of precipitation in your area, etc. Contact your local contractors for advice on the best type of waterproofing materials.

EPDM Rubber: 

  1. Ethylene propylene diene monomer or more commonly known as EPDM, is a synthetic rubber. 

  1. It is resistant to UV rays, abrasions, and the impact of weather. 

  1. It is also one of the most flexible and waterproof rubbers on the market, making it an ideal choice for roof waterproofing.

  1. EPDM Rubber is available in two thicknesses: 45 and 60 mils, and the cost will vary depending on the thickness you choose. 


  1. Another common roofing material is polyurethane. 

  1. They are plastic polymers, and there are many different polyurethanes, each with specific utilities. 

  1. Regarding their application in roofing, they are the strongest and most durable materials. 

  1. They are flexible and can withstand the roof structure’s daily movement (contraction and expansion).

  1. They are highly adhesive. They can stick to most roofing substrates.

  1. They can absorb the UV rays, in turn lowering the energy costs of the building and prolonging the life of the roof.  

  1. They also fill all the cracks on the roof and help decrease the water absorbency of the concrete.

Cementitious Coating: 

  1. The cementitious coating is mainly a mixture of sand, chemicals, and some silica-based substances. 

  1. When these ingredients are combined with lime to hydrate it, it creates a waterproof sealant. 

  1. It is easy to apply, which is why it is also a popular choice for many contractor. 

  1. However, unlike the other materials, it has little flexibility.


  1. Thermoplastic is a plastic polymer and is very popular in waterproofing. 

  1. This material becomes pliable at a specific temperature and can solidify when cooled. 

  1. This pliable property makes it easy for the contractor to seal the sheets or panels. 

  1. Thermoplastics are resistant to tears, abrasions, chemicals, oil, and fuel. 

  1. They are highly flexible, resistant to low temperatures, and withstand extreme weather conditions. 

PVC Waterproofing Membrane: 

  1. Polyvinyl Chloride membrane, commonly known as PVC membrane, is another widely used material for waterproofing roofs. 

  1. It is water-resistant and vapor permeable or breathable. 

  1. It can be reinforced with a base of glass fiber or polyester mesh to provide extra durability.

  1. It is easy to install and is very durable.

Bituminous Membrane: 

  1. Bitumen (asphalt or coal tar) is combined with a mix of organic liquids, making them very sticky. They have certain properties which make them an ideal material for roof waterproofing.

  1. They actively repel water.

  1. They are easy to install on roofs but can only be used on flat or low-sloped roofs.

  1. They are cost-effective as compared to other materials. 

Steps to waterproofing the roof: 

Once you have selected the material for waterproofing, it is essential to follow a step-by-step process to ensure that the waterproofing membrane sticks securely to your roof and stays durable. Knowing the basic step involved in waterproofing will help you quickly identify any faults during installation and ensure you are getting your money’s worth.

Step 1: Cleaning the substrate  

It is crucial to thoroughly clean the substrate or the roof deck and ensure it is free of debris or dust. A clean substrate will ensure that the applied liquid membrane will stick firmly to the substrate. A high-pressure washer can be used to eliminate any contaminants that can interfere with the adhesion of the membrane. Once the substrate has been cleaned, it must dry thoroughly before applying the membrane. 

Step 2: Priming the Surface

The next step after cleaning the roof is to prime the surface. Ensuring the primer covers the entire roof surface as it fills all the cracks is important. A primer also acts as a sealant for the roof’s surface, and it’s important to ensure that the waterproofing membrane sticks properly to the roof. If the primer is not applied correctly, it can lead to leaks in the roof, and you might have to do the process again. Again, ensure the roof’s surface is clean and dry before applying the primer. 

Step 3: Treating the roof details: 

Once you have applied the primer and the base coat, the next step is to check and seal all the nooks and corners of the roof. All the vents, skylights, and chimneys must be treated with sealants, and the edges, corners, pipes, vents, and drains. Flashing should be checked for damages and gaps, and gutters must be free from debris and waste. 

Step 4: Applying the waterproofing membrane: 

The next step is to apply the waterproofing membrane of your choice. As discussed above, many types of materials are available in the market. A minimum of two membrane layers is often applied to ensure a leakproof surface. It is imperative to allow the first layer to dry before applying the next one. 

Step 5: Applying a primer or sealant:

The last step is to apply a final layer of primer or sealant. This locks in the waterproofing membrane onto your roof and acts as a shield protecting your roof from external elements. Allow the sealant to dry completely before exposing your roof to rain or snow. 


Now that you have an understanding of the different roof waterproofing materials available in the market and the steps involved in waterproofing, you will be able to make an informed decision. 

If you have any further questions or queries, feel free to contact Tom and Jerry’s Roofing. You can schedule a free consultation with them at: 


bottom of page