Editor's note:

"General code for waterproofing of building and municipal engineering" is a mandatory specification of the full text. It cooperates with the technical provisions in laws, administrative regulations and departmental rules to form a "technical regulations" system, which is the basis of various specific technical specifications and procedures for building and municipal waterproofing. Any standard has a certain theoretical basis and technical background. Only when we have a macro understanding of it in theory, can we well understand and apply norms, and will not be entangled in a certain article locally to form a complete understanding of the ideological system. Zhejiang Luban waterproofing invited Professor zhangwenhua of Zhejiang University of technology to analyze some theoretical issues of the specification. I hope it will help you.

The phenomenon of water leakage from building exterior walls has been quite common, especially in the rainy southern and coastal areas, which not only affects the normal use of buildings, but also has a certain impact on the structural safety. The main reason for the external wall leakage is that the external wall waterproofing has not been paid attention to, and most architectural designs do not have the requirements of external wall waterproofing. The mandatory engineering construction code general code for waterproofing of building and municipal engineering (GB 55030-2022) implemented on April 1, 2023 has made mandatory provisions on exterior wall waterproofing, specifying that the waterproofing grade shall be determined according to the waterproofing category of building exterior wall engineering and the category of waterproof service environment, and the corresponding waterproofing fortification shall be carried out according to the waterproofing grade. Starting from the functional requirements of building exterior wall engineering for waterproofing, how to determine the waterproof fortification standard and waterproof grade of building exterior wall?

1. Waterproofing scope of building exterior wall works

The exterior wall of a building is a component that forms the boundary between indoor and outdoor buildings, and bears part of the load, protects against wind and rain, insulates heat, prevents noise, and prevents fire safety. Waterproofing of exterior wall works refers to the waterproofing treatment carried out on the exterior wall of a building to prevent rainwater, snow water, cleaning water, etc. from penetrating into the room and to protect the wall insulation layer, structural layer, etc. The waterproofing scope of external wall works generally includes the external facade of the entire external wall, as well as the door and window openings, awnings, waist lines, balconies, deformation joints, pipes protruding from the external wall and other node parts.

External wall waterproofing is generally connected at the coping of parapet and gable at the roof. The inner walls and coping of parapets and gables belong to the scope of roof waterproofing. The waterproof layer of the external wall and the waterproof layer of the roof shall be overlapped on the top surface of the parapet and gable, and then fixed with metal coping or reinforced concrete coping.

For buildings with basements, when the exterior wall of the building is on a vertical plane with the outer side of the basement exterior wall, the waterproofing of the building exterior wall shall be connected with the waterproofing of the basement exterior wall at the top plate surface, and the waterproofing layer shall be overlapped. When the external wall of the building falls on the top plate of the basement, the waterproof layer of the external wall and the waterproof layer of the top plate shall be overlapped at the corner of the external wall and the top plate. The waterproofing of building exterior wall without basement shall be terminated under the apron at the bottom of the exterior wall, and the termination shall be lower than the damp proof course of the foundation of the exterior wall.

2. Waterproofing grade of building exterior wall works

According to the general specification, the waterproofing grade shall be determined according to the waterproofing category of the project and the waterproofing service environment. Article 2.0.3 of the general specification specifies the waterproofing category of building external wall works. Class a refers to the external wall of civil buildings and industrial buildings sensitive to leakage, and class B refers to the external wall of industrial buildings whose leakage does not affect normal use; Article 2.0.4 the use environment of building exterior wall is classified. The annual precipitation P ≥ 1300mm is class I, 400mm ≤ annual precipitation P ＜ 1300mm is class II, and the annual precipitation P ＜ 400mm is class III. According to the provisions on waterproof grade in Clause 2.0.6, the waterproof grade of building exterior wall shall be selected according to table 1:

Table 1 Selection of waterproofing grade of building exterior wall

Civil buildings are the general name of buildings for people to live and carry out public activities. According to the use function, they are divided into residential buildings and public buildings. There is no doubt about the definition of waterproof category. Whether the industrial building is sensitive to leakage and whether the leakage affects the normal use shall be jointly determined by the architectural designer and the owner user, and shall be clearly indicated in the architectural design description.

According to the relevant data in the standard for building climate zoning provided by the meteorological department, for the external walls of civil buildings and industrial buildings sensitive to leakage, the division of areas requiring primary and secondary waterproofing is shown in Figure 1; See Figure 2 for the division of class I, II and III fortification areas of industrial buildings where the leakage of waterproof category B does not affect the use.

Figure 1 waterproofing zoning of class a project

Figure 2 waterproofing zoning of class B works

3. Relevant requirements of other standards for waterproofing of building exterior wall works

(1) General code for civil buildings GB 55031-2022

Civil architecture refers to buildings for people to live, live and carry out social life. It can be divided into two categories: one is residential buildings, such as dormitories, residences, apartments and villas; The other is public buildings, such as office buildings, schools, libraries, hospitals, gymnasiums, exhibition halls, cinemas, hotels, shopping malls, stations, wharves, airports, etc. The general code for civil architecture specifies the basic dimensions, technical requirements and general technical measures of building space and location. Article 6.2.3 specifies the requirements for damp proof and waterproof of the wall; Article 6.2.4 specifies the waterproofing and drainage requirements for exterior wall openings and external windowsills; Clause 6.2.6. specifies the waterproofing requirements when installing equipment or pipes on the wall; Clause 6.8.1 specifies the waterproofing requirements for deformation joints:

(2) Code for residential projects (Exposure Draft)

A house is a house for the daily living of a family, which outsiders are not allowed to enter at will. The code for residential projects puts forward relevant requirements in terms of residential environment, building space, structural safety, indoor environment and building equipment, and article 2.2.8 of the exposure draft puts forward requirements for waterproofing of residential buildings; Article 4.1.16 puts forward requirements for waterproofing of Balcony:

Author Zhang Wenhua

Professor, School of civil engineering,

 Zhejiang University of Technology