Leaks in photovoltaic rooftops are, in most cases, not due to poor-quality mounting brackets, but rather result from a failure to distinguish between different roof types and the application of a one-size-fits-all approach to waterproofing. Many construction teams drill holes and apply sealant in the same way regardless of the roof type; whilst this may seem quick and convenient, it frequently leads to subsequent problems such as water seepage, dampness and peeling.

Different roof structures vary in terms of materials, drainage methods and load-bearing characteristics; consequently, the methods used to secure photovoltaic mounting systems and the waterproofing techniques employed also differ.

I. Flat Concrete Roofs: Emphasis on Secure Anchoring and a Continuous Waterproof Membrane

Flat concrete roofs are characterised by high hardness and a solid substrate, making them the most suitable roof type for drilling and anchoring. They are commonly used in industrial and commercial buildings, as well as self-built homes with flat roofs. However, flat roofs drain slowly and are prone to water accumulation, placing higher demands on hole sealing and the integrity of the waterproof coating.

For photovoltaic installations, it is recommended to prioritise the use of chemical anchors to secure the mounting frames. Compared to expansion bolts, chemical anchors provide a tighter, more secure hold that does not loosen over time; they also result in smaller gaps around the holes, thereby reducing the risk of water ingress. After drilling, the holes must be thoroughly cleaned and dried before injecting the adhesive to ensure the interior of the hole is fully filled and compacted, leaving no cavities through which water can seep.

Once anchoring is complete, it is not sufficient to simply seal the anchor points; a large-area waterproof coating must be applied around the entire base. Apply multiple layers of weather-resistant waterproof coating to the base, the base of the bolts and the drilled holes, extending outwards to cover the existing waterproofing layer. This integrates the localised waterproofing at these points with the roof’s overall waterproofing system, preventing localised leaks caused by spot repairs or cracking in the surrounding area.

II. Glazed Tile/Terracotta Tile Roofs: Drilling holes in the centre of tiles is strictly prohibited; the focus must be on positioning the tiles to avoid such areas.

Tile roofs are made of brittle material that is prone to cracking, and their glazed surface is non-absorbent. If a hole is drilled in the centre of a tile, it is certain to result in micro-cracks, water seepage and water pooling during rainy weather, and such damage cannot be fully repaired. Ninety per cent of leaks in tiled roofs are caused by drilling in the wrong locations.

The installation of photovoltaic systems on glazed or clay tile roofs must adhere to one ironclad rule: drilling is permitted only at the overlapping joints between tiles; drilling into the centre of the tile surface is strictly prohibited. These joints naturally allow for expansion and contraction, are less prone to fracturing, and align with the roof’s existing drainage pathways, thereby minimising water pressure build-up.

At the same time, specialised tile-hook waterproofing pads and rubber sealing layers must be used. Flexible spacers should be employed to wrap around the metal contact points, preventing tile breakage caused by rigid compression whilst sealing gaps against capillary seepage. Waterproofing for tiled roofs does not rely on thick or excessive layers of adhesive, but rather on precise positioning and flexible protection to ensure the integrity of the tiles, sealed joints and unobstructed drainage.

III. Steel-framed colour-coated steel sheet roofs: Avoid drilling holes where possible; where drilling is unavoidable, ensure double sealing.

Colour-coated steel sheet roofs are lightweight, prone to rust and subject to significant thermal expansion and contraction; drilling holes at random is strictly to be avoided. As metal sheets are subject to constant vibration and deformation throughout the year, standard sealant applications are highly prone to cracking and delamination. This makes them the roof type with the highest incidence of leaks and the greatest maintenance requirements.

Therefore, the preferred approach for colour-coated steel roofing is a hole-free clamping solution. By utilising specialised roofing clamps to grip the corrugations, this method avoids damaging the panel surface or cutting through the existing waterproof coating, thereby eliminating the risks of leaks and rust at source. This is currently the optimal installation method for industrial building photovoltaic systems.

Where drilling is unavoidable due to specific installation conditions, a dual-seal process using specialised waterproof rivets for colour-coated steel roofing sheets combined with butyl waterproof tape must be implemented: the rivets feature built-in waterproof washers to secure the drilled holes, whilst the surface is then fully wrapped with high-adhesion butyl tape. This conforms to the curvature of the roofing sheets, withstands cracking caused by thermal expansion and contraction of the metal, and prevents water ingress through gaps and surface corrosion.