Project Overview The Brilliance BMW Shenyang Production Base is a model of Germany's "Industry 4.0" aligning with China's intelligent manufacturing, effectively driving the development of the local economy and the automotive industry chain. This article takes the roof waterproofing project of the South Machining Workshop in the Brilliance BMW Automotive Co., Ltd. engine plant construction project as an example to introduce the application of a TPO polymer waterproof membrane single-layer roofing system on the roof of an automotive plant.
The South Machining Workshop single-unit project covers an area of 14,677.2 m2, with a single-story main building and partial mezzanine. The building height from the outdoor ground level to the top of the parapet wall is 12.85 m. The main structure is designed for a service life of 50 years, and the building's fire resistance rating is Class II. The main plant building is a steel frame structure and a steel roof truss structure, and the roof uses profiled metal sheet composite insulation membrane waterproofing (Figure 1).
Figure 1. Brilliance BMW Automotive Co., Ltd. Engine Plant Project
2. Roof Waterproofing and Insulation Design
2.1 Roof System Structure Layers The roof waterproofing project of the South Machining Workshop of the Brilliance BMW Automotive Engine Plant adopted the Oriental Yuhong TPO single-layer roof mechanical fixing system. In this roof system, the TPO waterproof membrane layer is installed on the roof using fasteners in a point-fixing manner, and is required to withstand all external loads (wind loads, shrinkage deformation loads, etc.) to ensure the waterproofing and protective function of the roof system. The structural design of the TPO single-layer roof system is shown in Figure 2.
Figure 2 Roofing System Design
2.2 System Construction Layer Parameter Requirements
1) The main waterproofing material for the roof system is TPO waterproof membrane, i.e., thermoplastic polyolefin waterproof membrane. This material has good low-temperature flexibility, weather resistance, durability, and hot air welding performance, and can be well integrated with various roof insulation structures to form a roof insulation and waterproofing system. This project uses polyester-reinforced TPO waterproof membrane, 2.0 m wide and 1.5 mm thick, with hot air welding for the overlap joints.
2) The insulation layer uses Class A non-combustible rock wool. Under a compressive strength of 60 kPa, the compression ratio of the rock wool is no more than 10%; under a point load of 500 N, the deformation is no more than 5 mm. During construction, the rock wool is laid in double layers with staggered joints to prevent through-joints, and is fixed to the crests of the profiled steel base plate using sleeves and screws. This project uses 70 mm thick rock wool insulation boards laid in double layers with staggered joints.
3) The vapor barrier uses a 0.3 mm thick polyethylene (PE) film with a vapor permeability ≤25 g/(m²·d). Adjacent PE films overlap by 10 cm, and the overlap seams are sealed with 10 mm wide, 1 mm thick butyl tape and compacted with a pressure roller to prevent air bubbles. The overlap seams of the vapor barrier at parapet walls, roof access points, pipes, and other joints are also sealed with butyl tape to ensure complete isolation of indoor air and prevent indoor moisture from entering the upper insulation layer.
4) The profiled steel base plate is a 0.8 mm thick single-layer roof-specific double-sided galvanized profiled steel sheet.
3. Roof Waterproofing and Insulation Construction Methods and Challenges Analysis
3.1 Process Flow: Base layer cleaning → Laying vapor barrier layer → Double-layer staggered rock wool insulation board laying → Mechanically fixing rock wool insulation board → Laying TPO waterproof membrane → Mechanically fixing TPO waterproof membrane → Hot air welding TPO waterproof membrane → Inspection and acceptance.
This project uses single-layer roof-specific profiled steel sheets as the base slab. Before construction, it is necessary to protect the roof perimeter and openings, clean the base layer, and prepare for roof waterproofing and insulation construction.
3.2 Construction Key Points: Roof safety and waterproof tightness are two fundamental indicators of a high-quality roof system. They permeate the entire roof construction process, while standardized construction is the technical and organizational guarantee of project quality.
3.2.1 Roof Safety: The TPO single-layer roof system relies on the fasteners at the membrane overlap joints to resist wind loads, and the arrangement of the fasteners determines the roof's wind load resistance level.
In terms of wind load design, this project accurately calculated and determined the fastening method for the roof waterproofing layer based on internationally accepted load calculation standards and wind uplift test results, ensuring the safety of the roof during use.
The wind uplift load of a single-layer roof is related to various factors such as wind speed, building height, building location, roof slope, and building shape.
3.2.2 Waterproofing Tightness Besides the quality of the TPO waterproofing membrane itself, the quality of the hot-air welding of the membrane overlaps is crucial to the waterproofing tightness of the roof system.
The hot-air welding overlaps of the TPO waterproofing membrane, including long and short side overlaps and detailed node welding, are of paramount importance in the construction of a TPO single-layer roof system. Problems such as incomplete or false welds should be avoided. Incomplete or false welds refer to welds that are not firmly welded; they may appear to be welded on the surface, but can actually be torn apart by hand, making these areas prone to leakage. Standardized construction measures should be implemented to prevent incomplete or false welds by addressing their underlying causes.
1) TPO membrane that has been contaminated or exposed to the external environment for approximately 7 days must be cleaned before hot air welding. For contaminated membrane overlaps, first wipe away dust and debris with a damp cloth, then dry with a clean cloth, followed by thorough cleaning with a dedicated membrane cleaner, and finally dry with a white cloth. Welding should only proceed after the membrane cleaner has completely evaporated (approximately 15-30 minutes depending on ambient temperature), and the welding speed should be approximately 20% slower than normal.
2) Before formal welding begins or after a drastic change in temperature, a trial weld must be conducted to determine the optimal welding temperature and speed. The ambient temperature should not be lower than -10°C. Figure 3 shows the weld seam tearing at different welding temperatures and speeds (13-19°C). This project underwent a trial weld using combination A in Figure 3, i.e., a welding speed of 2.5 m/min and a temperature of 480°C.
Figure 3. Welding temperature and speed test and adjustment before formal welding.
3) Only when all roof construction conditions meet the requirements can the next step of construction proceed (except in special circumstances), striving for completion in one go. "Completion in one go" means completing the large surfaces, details, and finishing touches in the shortest possible time. If this is difficult to achieve, proper protection must be implemented, and the membrane at the welding area must be thoroughly cleaned before welding.
4) Isolation plates should be placed before welding the overlapping edges of the membrane, and also after welding to ensure that the welding torch insertion portion is properly welded (Figure 4).
Figure 4. Isolation plates placed before and after welding the overlap edge of the roll material.
5) For short side joints of the roll material, the lower roll material should be cut at an angle or with a notch as shown in Figure 5 (left); when welding, a partition plate should be placed to ensure welding quality while avoiding burns to the bottom roll material (Figure 5 (right)).
Figure 5. Key points to note for short side overlap
6) At the end of each workday or during rainy weather, sealing measures should be taken to prevent rainwater and moisture from entering the insulation layer.
7) At T-joints, the membrane rolls need to be cut to ensure welding effectiveness.
8) After the membrane rolls are welded, a special hook should be used to inspect the welds promptly. Any unwelded or weak welds should be addressed immediately to ensure the membrane rolls weld effectively.
3.3 Analysis of Construction Difficulties This project involves the machining workshop and engine assembly workshop of an automobile factory. The owner and management unit had high requirements for the detailed design of the roof waterproofing system. There are many roof walkway slabs connected to the roof via H-beams, resulting in numerous H-beam columns protruding from the roof, increasing the difficulty of waterproofing. Before waterproofing construction, based on the site conditions, the joints of the H-beam columns protruding from the roof were refined. A drip edge was welded to the H-beam columns to ensure waterproof sealing at this location, solving the waterproofing problem. The specific method is shown in Figure 6.
Figure 6 Waterproofing method for H-shaped steel columns
4. New Technology Application and Innovation
4.1 New Technology Application The mechanically fixed TPO single-layer roofing system adopted in this project is one of the new building waterproofing technologies promoted by the national construction authorities, and it has the following significant advantages:
1) It reduces the protective layer, making the roof lighter and saving a significant amount of building materials; TPO waterproof membrane is a green and environmentally friendly material, which can be recycled after reaching its service life, reducing construction waste.
2) It reduces energy consumption inside the building, saving energy and reducing emissions.
① The light-colored TPO single-layer roofing system used in this project is a cold roofing system. Its high solar reflectance index and retention rate allow the membrane to reflect a large amount of solar radiation, reducing heat conduction downwards, lowering the internal temperature of the factory in hot summers, reducing the energy consumption of refrigeration equipment, and conforming to the design concept of green building.
② The single-layer roofing system uses sleeves and screws for mechanical fixing, without compressing or separating the insulation layer, reducing thermal bridges, and providing excellent insulation performance.
3) Oriental Yuhong TPO waterproof membrane has a special functional resin layer on its surface, which is smooth, colorfast, easy to clean, and has a low dust absorption rate, providing long-lasting energy-saving effects. While ensuring the membrane's welding performance, it is also more resistant to aging and acid rain, resulting in a longer service life.
4) Mechanized construction saves time. The construction process utilizes numerous mechanized tools, including automatic hot air welding machines, effectively ensuring the quality of the waterproofing project while reducing the labor intensity of workers and improving construction efficiency.
5) Reliable waterproofing effect reduces maintenance costs. Based on the thermoplasticity of TPO, the membrane can be processed into various shapes after heating, simplifying joint construction and enabling various special roof designs to meet the construction requirements of complex details, ensuring no leaks to roof pipes and equipment. Furthermore, TPO membranes allow for flameless construction, making them environmentally friendly.
6) During the construction of the mechanically fixed TPO single-layer roofing system, the membrane is laid loosely on the base layer, with mechanical fixing only at the overlap joints. The homogeneous membrane used in the detailed nodes has an elongation at break of over 500%, allowing the system to adapt to large base layer deformations. It is a fully assembled construction method with no wet work, resulting in fast construction speed, making it a perfect choice for large-span steel structure buildings.
4.2 Innovations of this Project
4.2.1 Waterproofing Treatment of H-shaped Steel Columns Exposing the Roof
To ensure waterproofing tightness, the columns protruding from the roof of the single-layer roofing system should use regular cross-sections, such as circular columns or square steel columns, avoiding irregular cross-sections such as angle steel, channel steel, and H-beams. However, this project extensively uses H-beam columns, posing a significant challenge to the construction and waterproofing tightness of the TPO membrane.
After numerous trials and discussions, the final solution was to replace the H-beams with rectangular steel for the joints (see "3.3 Analysis of Construction Difficulties"). This innovative approach solved the feasibility and waterproofing issues of irregular cross-section column joints, laying the foundation for the waterproofing safety of the entire roof system.
4.2.2 The roll material surface has an easy-clean layer. For large factory roofs, cleaning is a very troublesome problem. A dusty roof not only affects aesthetics but also reduces sunlight reflection, increasing indoor energy consumption.
General TPO materials have a rubber-like surface, which is relatively rough and has a high coefficient of friction. Once contaminated during use, the surface is difficult to clean, especially at overlapping areas and detailed joints during construction. This can lead to the risk of incomplete welds during welding, resulting in potential leaks later in the project.
To address this issue, Oriental Yuhong developed a TPO waterproof membrane with an easy-clean layer. During use, it exhibits better scratch resistance, organic solvent resistance, gas barrier properties, and lower water absorption and coefficient of friction. It also reduces the static electricity that attracts dust to the surface. When using organic solvents to clean surface contaminants, it is less likely to damage the surface structure, and the contaminants are easier to wipe away.
