Roof Waterproofing

But its purpose is slightly different, so moisture can pass through the roofing material, which is acceptable and even normal in some cases. The real barrier on its path, which in fact protects the roof from getting wet, is waterproofing.

Different materials can be used for waterproofing depending on the type of roof: from mastics and the widely known roll roofing (rubberoid) to modern super-diffusion membranes. The choice depends on specific conditions and the roof structure. Therefore, it's essential to first determine the roof structure components, and the selection of waterproofing will follow naturally.

Coating Waterproofing: Mastics

As a standalone waterproofing method, mastics are used for flat, liquid-applied roofs. However, they are more commonly used as auxiliary insulation. Specifically for:

• repairing roll roofs, sealing cracks and misaligned joints of roll material;
• adhering roll insulation;
• sealing pipe vents, skylights;
• additional insulation of valleys, eaves, ridge sections;
• attaching bituminous shingles.

Mastics cannot be used as standalone waterproofing for sloped roofs. For mastic roofing, the base must be thoroughly cleaned of dust, dirt, and flaking parts. Often, it is recommended to additionally prime the base with bituminous primer or degreasing agent.

Rubberoid

Used for roofs with a slope from 0 to 25%. Very popular and widely used. One reason is its low cost. However, it is rapidly losing favor. The issue lies in its limited durability — after several years of use, it may show defects: the cardboard base rots, bituminous material degrades under UV exposure, integrity is compromised, and leaks begin. Moreover, its base consists entirely of flammable materials.

A more modern alternative with some drawbacks removed is European rubberoid. It uses non-rotting base materials (glass fiber, polyester, glass mat), coated with modified bitumen. It is more durable than its predecessor but still not eco-friendly and flammable. It is significantly more expensive than standard rubberoid. Therefore, using European rubberoid for small roofs is often not cost-effective. But it’s suitable for flat roofs.

Pergammin

Pergammin was once a very popular roofing waterproofing material. It replaced rubberoid but has now lost popularity. The reasons: non-eco-friendly, low strength, rapid aging, and loss of insulating properties. It's the cheapest option, but equally short-lived. Therefore, it should only be used for temporary roof protection.

Films and Membranes

Term "waterproofing films" refers to membranes made from PVC or polypropylene. These materials are gaining popularity for several reasons:

• high base strength,
• excellent waterproofing performance,
• long lifespan (up to 50 years),
• breathability (vapor permeability).

They are divided into pseudo-diffusion, diffusion, anti-condensation, and super-diffusion membranes. Each type has its own purpose and application specifics. Naturally, membrane prices are relatively high compared to other waterproofing materials, and cost often correlates with performance.

Pseudo-diffusion membranes are films with low vapor permeability: up to 300 g/m²/24 h, typically ranging from 30–50 g. These can be used to protect cold roofs, with no usage restrictions in such cases.

If used in insulated roof structures, a ventilation gap must be created between the membrane and insulation. This gap is mandatory and requires additional sheathing. Therefore, the cost of such insulation may rise to match that of standard diffusion membranes.

Diffusion and super-diffusion membranes are perforated films with medium (400–1000 g/m²/24 h) and high (over 1000 g/m²/24 h) vapor permeability, respectively. Such permeability is considered sufficient for roofing. With these films, a ventilation gap is not required. Key features:

• can be installed directly on insulation;
• blocks moisture from entering the roof structure while simultaneously releasing internal vapor;
• acts as wind protection for insulation, helping retain heat in the under-roof space;
• retains performance even in dusty environments;
• forms condensation on the upper surface when releasing vapor, so they must not be used under roofs prone to corrosion.

If the finish layer is metal (steel, zinc, copper, aluminum), use diffusion-type volumetric membranes. The layer in contact with the roofing material acts as a separator, absorbing and thus diverting condensation away from the metal roof.

Anti-condensation membranes are also used for metal tile and corrugated roofs. One side of the film has a fluffy fleece. This side should face outward, toward the finish layer.

A ventilation gap must be created under the membrane, as its vapor permeability approaches zero. When choosing such a film, look for the lowest possible vapor permeability, since it must not allow moisture to reach the finish layer.

Properly selected waterproofing extends the lifespan of both the roofing and insulation, and the entire roof structure. Therefore, choosing protection against moisture should be done with care.