When waterproofing CAUSES leaks

It is an often overlooked fact, but the incorrect application of waterproofing is responsible for many leaking roofs across South Africa today. The market is flooded with a wide range of liquid-applied waterproofing products, including acrylics, polyurethanes, bitumens, and liquid rubber. These products are manufactured by nearly every paint company and are available in almost every hardware store, making them easily accessible to homeowners, handymen, and professional contractors alike. While the quality of these products varies, all can perform effectively if applied correctly and in the appropriate situations. The key differences lie in their durability and cost.

However, problems arise when waterproofing systems are applied indiscriminately to roofs, sealing the wrong components. While this might provide a short-term solution, it often leads to far more serious issues in the long run than the original problem it was meant to solve.

Incorrect Sealing of Tiled Roofs

Tiled roofs should not be sealed because doing so can trap water beneath the waterproofing layer. This issue can occur immediately if the waterproofing has been poorly installed, or it may develop over time as the sealant weathers and begins to form pinholes. During heavy or prolonged rainfall, water can penetrate the coating, preventing the tile from functioning as intended and funneling water into the house.

The only components on a tiled roof that should be sealed using a waterproofing membrane are:

• Ridge cappings
• Flashings to head and side wall parapets
• Flashings around chimneys and skylights
• Broken tiles (only as an emergency measure when no replacement tiles are available)

The following elements on a tiled roof should never be sealed:

• Valley flashings
• Tile overlaps where they adjoin
• The entire roof surface with a waterproof coating
• Roof tiles with paint applied so thickly that it clogs the joints and glues the tiles together

A tiled roof is designed not to be sealed. If you examine the design and profile of a roof tile, it is intended to keep water out without the need for additional sealing. The thickness and density of a concrete tile, when laid at the correct slope, make it impermeable to water, even during extended periods of rain. When tiles are overlapped according to specified widths on a correctly pitched roof, water cannot breach these overlaps. Additionally, where tiles overlap side by side, their special design incorporates two rows of grooves along the edge of each tile, allowing them to interlock and prevent water from spilling over.

Conclusion

While certain components of a tiled roof can be waterproofed or sealed, the general rule is that the roof should be repaired and reinstated to its original state, as it was designed and built. The application of waterproofing should be reserved for specific areas where it is needed, rather than being used to seal the entire roof, which could ultimately lead to more harm than good.

Incorrect Sealing of Metal Roofs

Metal roofs, commonly found on factories, shopping centres, and other commercial properties, often feature profiles such as corrugated, IBR, and Kliplok. There are also lesser-known variants and many profiles that are no longer available on the market, making repairs to these roofs particularly challenging.

The areas on a metal roof that can be safely sealed are:

• Counter flashings to parapet walls
• Box gutters
• Holes and splits in roof sheets
• Penetrations such as pipes and ducts

However, the following components on metal roofs should never be sealed:

• Side overlaps
• End overlaps
• Head and side wall flashings
• Roof screws
• Ridge cappings
• Back flashings

Similar to tiled roofs, metal roofs are designed to function without the application of waterproofing bandages. Metal roofs must accommodate significant expansion and contraction, known as thermal movement. The roof fasteners on corrugated and IBR roofs are specifically designed to manage this movement. Ensuring that roof sheets are not overly long allows for end-to-end movement through overlaps. On large structures such as warehouses and shopping centres with long single-span sheets, the sheets are often fastened with concealed clips that allow for substantial movement as the sheets slide on the clips. Importantly, on all metal roofs, the head and side wall flashings should not be fastened to the roof, allowing all components to move independently of each other.

Serious Problems from Incorrectly Sealing Metal Roofs

Indiscriminate sealing of metal roofs can lead to several serious issues:

• Worsening leaks: Water can become trapped under the waterproofing layer, exacerbating the problem that was initially intended to be repaired.
• Rusting of roof sheets: Water trapped under overlaps can cause roof sheets to rust, leading to large-scale repairs and, in some cases, complete roof replacement.
• Unsightly repairs: Repairs made with waterproofing materials can be visually unappealing unless the entire roof is repainted, which incurs additional expense.
• Increased maintenance costs: Waterproofing materials require reapplication every few years, adding to the ongoing cost of roof maintenance.

As with tiled roofs, only a limited number of components on a metal roof should be sealed with a waterproofing membrane. The roof should otherwise be restored to its original design and condition. For example, if screws, flashings, or ridge cappings are faulty, or if roof sheets are damaged, they should be replaced. Butyl sealing tape is a useful product to install between roof sheets and flashings, offering much greater longevity than waterproofing bandages with no maintenance required. Additionally, if flashings or other components are undersized or incorrectly installed, they should be rectified accordingly to ensure the roof functions as intended.