In April 2018, the "General Specification for Waterproofing of Building and Municipal Engineering" was included in the mandatory specification research and compilation plan of the Ministry of Housing and Urban Rural Development, and was officially approved for project preparation in January 2019. After more than 4 years, on October 24, 2022, the Ministry of Housing and Urban Rural Development issued the full mandatory standard "General Specification for Waterproofing of Buildings and Municipal Engineering" (hereinafter referred to as the "General Specification for Waterproofing"), which will be implemented on April 1, 2023. The general waterproof standards start from comprehensively improving the design service life of engineering waterproofing, determining the engineering waterproofing level through the engineering waterproofing category and the engineering waterproofing use environment, clarifying the material engineering requirements, improving the durability, reliability, environmental safety of waterproof materials, enhancing the waterproof fortification requirements, increasing the number and thickness of waterproof channels and other fortification measures, as well as design, construction, acceptance, operation and maintenance requirements, comprehensively improving the quality of engineering waterproofing, and laying a good foundation for reducing building leakage and curing the stubborn problem of leakage.

Background

1. Reform of standardization work in engineering construction

In March 2015, the "Notice of the State Council on Issuing the Reform Plan for Deepening Standardization Work" (Guofa [2015] No. 13) was released, marking the official launch of the country's deepening standardization reform work. In order to implement the State Council's standardization reform work plan, in August 2016, the Ministry of Housing and Urban Rural Development issued the "Opinions on Deepening the Reform of Engineering Construction Standardization Work" (Jian Biao [2016] No. 166), which set the long-term goal of the government formulating mandatory standards and social organizations formulating voluntary adoption standards. By 2020, the management system that adapts to the development of standard reform will be basically established, important mandatory standards will be issued and implemented, government recommended standards will be effectively streamlined, and group standards will have a certain scale. By 2025, a standard system with mandatory standards as the core and recommendatory standards and group standards as the supporting standards will be initially established, the effectiveness, progressiveness and applicability of standards will be further enhanced, and the international influence and contribution of standards will be further enhanced. Clearly propose seven major goals for the reform of engineering construction standards, including accelerating the formulation of mandatory standards throughout the text, building a mandatory standard system, and comprehensively improving the level of standards. In this context, the pre research and compilation of mandatory standards related to the fields of architecture and municipal engineering have been put on the agenda. Mandatory standards have mandatory binding force, ensuring the safety of people's lives and property, personal health, engineering safety, ecological environment safety, public rights and interests, as well as promoting the conservation and utilization of energy resources and meeting the control bottom line requirements of social and economic management. The names of mandatory standard projects are collectively referred to as technical specifications. Technical specifications are divided into engineering project categories and general technical categories. Engineering project specifications are mandatory standards that focus on the overall scale, planning layout, project functionality, performance, and key technical measures of engineering projects. General technical specifications are mandatory standards aimed at technical specialties, with general technical requirements such as planning, surveying, measurement, design, and construction as the main content.

2. Waterproofing is a fundamental functional requirement of construction engineering

Humans moved from caves to plains, using branches and leaves to build shelters on trees to avoid wind, rain, and wild animals. Later, they used soil as walls, and thatch, natural stone slabs, and rammed earth with long leaves to guide water, were used to build houses. The Qin and Han dynasties invented bricks and tiles, starting with the use of bricks for walls, tiles for roofs, and dense multi-layer stacked tiles with certain waterproof capabilities for roofs. They also used steep slopes to drain water away, achieving the purpose of sheltering from wind and rain. In modern times, asphalt rolls made mainly of natural asphalt and petroleum asphalt were used. The method of stacking two felt, three oil, three felt, and four oil asphalt rolls formed a fully enclosed waterproofing system mainly based on material waterproofing. The sloping roof was gradually changed to a flat roof. In modern times, modified asphalt rolls, composite polymer rolls, waterproof coatings, and other alternatives to asphalt rolls are used for roof waterproofing. The purpose is still to provide shelter from wind and rain, and to provide a good living environment for people's lives and production. The green, energy-saving, environmentally friendly, ecological, and intelligent technologies of buildings all rely on a safe and reliable platform for healthy development. Building waterproofing is one of the most basic guarantees of this platform. Building water leakage often causes mold and poses a health hazard. And it breeds neighborhood conflicts, leading to disputes. With the improvement of living standards and decoration standards, people are particularly sensitive to leaks. Building waterproofing failure may result in damage to facilities and property. The long-term invasion of water can rot wooden structures, harm steel structures, cause steel corrosion, develop concrete cracks, damage the main structure, and shorten the safe service life. In multiple mandatory standards such as the "General Code for Civil Buildings" GB 55031-2022, the "Code for Dormitory and Hotel Building Projects" GB 55025-2022, and the "Residential Project Code" (draft for comments), waterproof requirements have been proposed for the basement, roof, exterior walls, and interior of building projects.

3. The leakage rate remains high, and the proportion of leakage in complaints about construction quality remains high

Water leakage has always been one of the common quality problems in construction projects, which has long plagued the production and life of the people. Multiple units and departments in China have conducted investigations on water leakage in construction projects. The statistical data on leakage rate, reasons for leakage, and service life of waterproof layers are as follows:

(1) Leakage rate

In a survey of 100 cities nationwide in 1996, the leakage rate was as high as 60%, with some cities reaching as high as 80% to 90%. The China Building Technology Research Center conducted a survey on the leakage situation of houses built within the past 10 years. In 17 provinces, 22 cities, and 327 buildings, leakage accounts for 60%. In 2008, the Ministry of Construction organized 100 cities to conduct leakage investigations on houses completed between 1998 and 2000. Randomly inspect 20 projects in each city, including public buildings, factories, and residential buildings, with residential buildings accounting for 50%. The scope of investigation includes roofs, toilets, and basements. Among the 2072 buildings sampled, 24.5% were completed in 1998; Completed in 1999 accounted for 35.1%; Completed in 2000 accounted for 40.4%; The total area is about 8 million square meters. The survey results show that roof leakage accounts for 35%; Toilet and bath 39.2%; In the spring of 2011, relevant departments in Hainan conducted investigations on 37 projects in Haikou, Sanya, and Qionghai cities, and found that 32 projects had varying degrees of leakage, accounting for 86.5%; Among them, 17 have serious leakage, affecting the overall structure and building life. At the end of 2012, the spot check results of waterproof materials in Guangzhou showed a sharp decline in their qualification rate: 73.30% in 2010; In 2011, it was 61.11%; In 2012, it was 43.75%. In 2014, the China Building Waterproofing Association released the "2013 National Building Leakage Survey Project Report" based on the national building leakage survey. The survey report selected 28 large and medium-sized cities and 850 communities across the country for investigation. Roof samples were obtained through field surveys and home visits, with an average of 100 or more buildings per city, totaling 2849 buildings and corresponding to 1777 basements; The household samples were intercepted and visited by interviewers in the community where the building samples were located, with an average of over 100 per city, totaling 3674. This survey mainly covers roofs and basements built in the past 20 years, with an average construction time of 2004 for buildings. The survey shows that the national average roof leakage rate is 95.33%. Among the building samples surveyed in 28 cities, 19 cities have roof leakage rates higher than the average level. Among them, 16 cities have a roof leakage rate of 99.00% or above, and roof leakage is extremely common in the vast majority of cities. The average basement leakage rate nationwide is 57.51%, and among 28 cities, 12 cities have basement leakage rates higher than the average level. Some cities have basement leakage rates exceeding 70%. Although there has not been a comprehensive investigation into the leakage situation in recent years, it can be seen from the engineering quality situation reports released by relevant institutions such as construction supervisors and industry associations that the leakage rate of construction projects is still high. In the complaints about construction project quality, the proportion of complaints about leakage problems is still high. For example, in 2020, housing leakage complaints accounted for 33.3% of the total number of engineering quality complaints in Beijing.

(2) Reasons for leakage

The causes of building water leakage involve multiple aspects such as materials, design, construction, and management and maintenance. The material quality mainly affects the durability of the waterproof layer; Unreasonable design can affect the effectiveness of waterproofing, the feasibility and difficulty of waterproofing construction, and the durability of the waterproofing layer, among other aspects; The quality of construction is directly reflected in the effectiveness of waterproofing engineering. If leakage occurs in some projects that have not yet been put into use, there must be construction quality problems; Poor management and maintenance during use can also cause leakage, such as damage to the waterproof layer of roof installation equipment, falling leaves covering water outlets causing poor drainage and backflow. According to the analysis of the causes of leakage in engineering projects conducted over the years, unreasonable waterproof design accounts for 20% to 25%, poor construction quality accounts for 40% to 50%, unqualified material quality accounts for 20% to 25%, and inadequate management and maintenance accounts for 8% to 12%.

(3) Service life of waterproof layer

The service life of the waterproof layer is related to the quality of the material and the usage environment. The usage environment includes high temperatures caused by wind, frost, rain, snow, sunlight, ultraviolet rays, ozone, acid and alkali salt ions, mold and other microorganisms in the atmosphere. These factors have an aging effect on the waterproof material, causing the waterproof layer to gradually become ineffective. The average service life of waterproof layers in different years without considering differences in environmental conditions: 1950-1958, with an average of 26 years; From 1958 to 1964, with an average of 20 years; From 1964 to 1976, with an average of 16 years; From 1976 to 1980, with an average of 10 years; From 1980 to 1990, with an average of 5 years; After 1990, an average of 3 years; In recent years, many projects have been completed but missed in the same year. The normal service life of the waterproof layer is getting shorter and shorter. This statistical data may have issues with judging water leakage. Before the 1980s, people had relatively low requirements for waterproofing, and it was acceptable for there to be a small amount of wet stains, mold, etc. on ceilings, walls, etc. However, since the 1990s, the requirements for waterproofing have increased, and wet stains, mold, etc. are also symptoms of waterproofing failure. This is one of the reasons for the low service life of waterproof layers in recent years. However, it is an undeniable fact that the quality of waterproof materials has declined, especially in terms of durability.

4. The necessity of formulating mandatory standards

The hazards caused by water leakage are multifaceted. Water leakage can lead to mold growth in building interiors, breed mold, and keep the interior in a damp state for a long time, posing a threat to human health; Leakage of water can cause damage to indoor decoration, detachment of suspended ceilings, and other hazards, resulting in property damage; Leakage can accelerate the rate of structural damage and reduce the durability of building structures. As a waterproofing project that ensures the basic functional requirements of buildings, the safety of people's lives and property, personal health, and engineering safety, it is necessary to develop mandatory standards.

Author Zhang Wenhua

Professor, School of civil engineering, Zhejiang University of Technology