Terminal Roof Waterproofing Construction and Maintenance I

Terminal roofs often cover tens of thousands of square meters. If a leak occurs in a single-story roof, the spaces directly below—such as check-in halls, waiting areas, and baggage sorting facilities—are high-value areas that are directly threatened, posing a risk to airport operations and the passenger experience. Waterproofing design adheres to the principle of “combining prevention, drainage, interception, and sealing; prioritizing prevention; implementing multiple lines of defense; integrating flexible and rigid measures; adapting to local conditions; and adopting a comprehensive approach.”

1. Roof Drainage

Roof drainage and waterproofing are two closely related and mutually reinforcing components of a building’s roof system. Drainage is a prerequisite for waterproofing; an effective drainage system can rapidly remove rainwater or melted snow from the roof, reducing the time water remains on the surface and minimizing erosion and waterlogging. If the drainage system is inadequate, rainwater will accumulate on the roof, increasing the roof load and accelerating the aging and deterioration of the waterproofing layer. Waterproofing is the safeguard for drainage; if the waterproofing layer is damaged or fails, water will penetrate into the roof structure, affecting the normal operation of the drainage system.
The design of the drainage system must take into account the performance of the waterproofing layer, including its load-bearing capacity and service life. The drainage slope should ensure that rainwater flows smoothly toward the drainage outlets while avoiding excessive water flow impact on the waterproofing layer. Drainage outlets, gutters, and other drainage facilities should be located within the protected area of the waterproofing membrane to ensure that the drainage facilities themselves are not damaged by leaks. If the drainage system is poorly designed or constructed, water flow may erode the waterproofing membrane, leading to damage. Blockages in the drainage system can cause water accumulation, which subjects the waterproofing membrane to prolonged immersion, accelerating its aging and failure.

The design of the waterproofing membrane must account for the requirements of the drainage system; the membrane must be capable of withstanding the pressure and water flow impact generated by the drainage system’s operation. Joint details around drainage facilities should be reinforced, as damage to the waterproofing membrane can impair the normal operation of the drainage system. Improper installation of the waterproofing membrane may lead to issues such as leaks in the drainage system during use. For example, when installing rainwater inlets, ensure the waterproofing membrane is properly sealed to prevent rainwater from seeping around the inlet.

2. Waterproofing of Concrete Roof Structures

The standard approach for concrete roofs in terminal buildings can be divided into four layers: structural configuration, crack control, waterproofing and thermal insulation, and detail joints. Based on the design of a concrete roof for a certain airport terminal, the structural configuration layer, from top to bottom, consists of:

1) A 40mm-thick C30 fine-aggregate concrete protective layer, reinforced with a φ4@200×200 steel mesh, troweled and finished immediately after placement;

2) A non-woven polyester fiber fabric or PE film separation layer;

3) An upper layer of 2 mm thick polymer waterproofing membrane + a lower layer of 1.5 mm thick polyurethane coating;

4) A 20mm-thick 1:3 cement mortar leveling layer (2% sand content), with a minimum thickness of 80mm of foam concrete or aerated concrete;

5) A 50mm-thick extruded polystyrene board insulation layer, dry-laid with staggered joints;

6) A cast-in-place reinforced concrete roof slab with a thickness of ≥120mm, water resistance grade P6, poured in a single continuous pour; 7) Depending on architectural requirements, a 20mm-thick fire-resistant coating and surface finish layer.

Typical Construction Sequence: Substrate cleaning → Structural water-tightness test → Slope formation layer → Insulation layer → Leveling layer → Waterproofing layer (membrane + coating) → Separation layer → 40mm fine aggregate concrete protective layer (reinforced, with 6m×6m contraction joints filled with weather-resistant sealant) → Curing for no less than 14 days → Second water retention test for 48 hours with no leakage → Handover.

Roof parapets, equipment foundations, and parapet walls must be cast in place with the roof slab in a single pour. At expansion joints, curtain wall interfaces, rainwater outlets, and pipe penetrations, a 500mm-wide reinforced membrane layer is added to the double-layer waterproofing. When using a siphon rainwater system, an additional membrane waterproofing layer is installed in the eaves gutter, followed by a water retention test.

3. Metal Roof Waterproofing

Waterproofing for steel-structured roofs differs from that of concrete roofs. It no longer relies on a single waterproofing method but instead employs a three-layer defense system—or three or more waterproofing layers—comprising “continuously welded metal or stainless steel panels + flexible membrane + membrane coating at joints.” This is further supplemented by systems such as siphon drainage, overflow outlets, and gutter heating for snow melting to collectively ensure zero leakage.

1) Structural waterproofing of the metal panels themselves: Standing seam aluminum-magnesium-manganese panels, 360° rolled-edge color-coated steel panels, or stainless steel hidden-clip panels. Panel thickness ≥0.9 mm, slope ≥5%, longitudinal overlap ≥200 mm. All panels are secured using concealed fasteners to eliminate water leakage through nail holes.

2) Butyl rubber sealing tape is laid continuously beneath the standing seam. Additional flashing tape is applied at the ridge, eaves, and gable ends to form a “secondary seal.”

3) Composite membrane/coating integrated waterproofing layer: Option A: 1.8 mm thick TPO membrane + 0.6 mm thick galvanized steel composite panel. Option B: 2 mm thick single-component polyurethane waterproof coating, reinforced with non-woven fabric.

Metal Roof Waterproofing Methods:

1) Self-waterproofing with standing seam metal roof panels. Typical profiles include 65/400 and 75/400 aluminum-magnesium-manganese or galvanized steel sheets, with rib heights of 65–75 mm. The 360° interlocking creates a cavity for water drainage. This can serve as the primary waterproofing layer or is often used as a decorative or structural layer.

2) Self-waterproofing with continuously welded stainless steel sheets: 0.5 mm thick profiled stainless steel sheets are fully continuously welded using automatic welding machines, resulting in a nail-free, hole-free, and fully airtight and watertight structure; backed by 1.5 mm thick self-adhesive modified bitumen membrane.

3) Single-layer flexible membrane system: profiled steel sheet → PE vapor barrier → rock wool/glass wool insulation → 1.5 mm thick TPO or PVC membrane (mechanically fastened + hot-air welded) → topped with metal flashing or standing seam panels as needed.

4) Double-layer or multi-layer composite systems, combining “metal sheet + flexible membrane” or “metal sheet + coating + membrane.”

5) Coating-based waterproofing, primarily used for leak repairs on existing terminal buildings or for irregular joints such as skylights, eaves, and ridges. Typically employs a “three-coat-one-fabric” process (primer + intermediate coat + polyester non-woven fabric reinforcement + topcoat), with colors customizable to match the roof.

6) Integrated waterproofing for special-shaped curtain walls and roofs: When the boundary between the roof and curtain wall is complex (e.g., Shenzhen T3 Terminal), use rigid flashing panels + flexible membrane edging + water drainage channels + removable cover plates.