The mandatory engineering construction code general code for waterproofing of building and municipal engineering gb55030-2022, which will be implemented on April 1, stipulates that the waterproofing design service life of roof engineering shall not be less than 20 years, and the waterproofing grade shall be determined according to the waterproofing category and annual precipitation of roof engineering. What is the difference between this and the current technical code for roof engineering GB 50345-2012?

1. Technical code for roof engineering GB 50345-2012 specifies the waterproof grade of roof

Article 3.0.5 of the technical code for roof engineering (GB 50345-2012) specifies the basis for determining the waterproof grade of the roof and the fortification requirements.

The high-rise buildings in the provisions are relatively clear, while important buildings or general buildings are independently determined by the owner and architect according to the project. The article also stipulates that special waterproofing design shall be carried out for building roofs with special requirements for waterproofing, and the waterproofing requirements can be higher than class I. Since its implementation in 2012, the proportion of waterproof fortification according to the waterproof grade is relatively large.

2. General code for waterproofing of building and municipal engineering (gb55030-2022) specifies the roof waterproofing grade

The general specification stipulates that the working life of waterproofing design of roof works shall not be less than 20 years, and the waterproofing grade shall be determined according to the waterproofing category of the project and the use environment. In combination with the waterproof category of roof works in article 2.0.3 of the general specification and the use environment in article 2.0.4, and according to the waterproof grade in article 2.0.6, the waterproof grade of roof works shall be selected according to the following table:

(1) Waterproofing category of roof works

The general specification is to determine the waterproof category of roof works according to the possible impact of leakage according to the functional requirements of roof waterproofing, on the premise that the roof does not leak within the working life of the engineering waterproof design. Due to the different use functions of buildings, once the roof of some buildings leaks, it may cause explosion and cause casualties. If the roof of some buildings leaks, important equipment or precious items will be damaged, or products will be polluted and damaged; Some buildings, such as roof leakage, will bring great impact and inconvenience to production and life; Some buildings, such as roof leakage, will pollute and mildew the interior decoration, affecting the use function and beauty. Therefore, when dividing the waterproofing categories of roof works, according to the influence degree caused by leakage, the following situations shall be considered: huge losses will be caused after leakage, even personal casualties; Or the leakage will cause great economic losses; The leakage water has certain adverse effects on the health, property and building functions of personnel; The water leakage will not affect the normal use function or cause economic losses. The roof waterproofing category is determined to be divided into class A, class B and class C. The determination of project waterproofing category and applicable project types can be determined by the project designer according to the actual situation of the project by referring to the table below.

(2) Use environment

Different environmental conditions have different effects on the waterproofing system. The main factors affecting the waterproofing system are precipitation, wind pressure, ozone, ultraviolet light, temperature, humidity, acid, alkali and salt in the atmosphere, etc. Ozone, ultraviolet, temperature, humidity, acid, alkali and salt in the atmosphere mainly affect the durability of the waterproof system. Besides the durability, precipitation and wind pressure are also the factors affecting the failure probability of the waterproof system. When the impact degree is large, the fortification requirements are relatively higher; In the waterproofing of roof works, precipitation is the most important influencing factor. Therefore, article 2.0.4 of the general specification classifies the waterproofing environment of roof works according to precipitation.

The article takes the annual precipitation as the benchmark, and the annual precipitation of each region is different every year. The following figure shows the annual precipitation statistics of Hangzhou from 2000 to 2021. The annual precipitation from 2003 to 2006 was less than 1300mm. According to the annual precipitation in the past 21 years, the engineering waterproof environment in Hangzhou should belong to class I, but it can also belong to class II. How to determine it needs to be explained in more detail.

Rainstorm intensity has a great influence on roof waterproofing, especially for roof drainage, which is a decisive factor in the design of drainage system. When the project designers determine the roof waterproofing grade, in addition to the two main factors of roof engineering waterproofing category and annual precipitation, they should also consider the impact of rainstorm intensity, wind pressure, ozone, ultraviolet, temperature, humidity, acid-base salt in the atmosphere and other factors on the roof waterproofing, so as to reasonably determine the roof waterproofing grade.

Author Zhang Wenhua

Professor, School of civil engineering, Zhejiang University of Technology

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