The core technology is to set up a steam exhaust channel inside the insulation layer and the leveling layer, so that the excess water in the base layer can be discharged into the atmosphere through this exhaust structure, which can effectively reduce the bulging of the membrane waterproof layer, and can also inhibit the cracking of the membrane and the leakage of the roof.
Roof exhaust ducts
1. Why do you want to do it?
On the question of why the roof should be used as a steam exhaust pipe, we recommend reading the research process and core technology of "roof exhaust structure", which was published in the 11th issue of "China Building Waterproofing" in 2015, author: Ye Linchang, institution: China Construction Industry Association Building Waterproof Branch. This article is an introduction to the research process and core technology of "roof exhaust structure" by Professor Ye Linchang, a well-known expert in building waterproofing, and explains the causes and consequences of this technology.
1 The mystery of roof bubbling
At the end of 1961, shortly after the 15,000 m³ reinforced concrete rectangular (30mx90m) crude oil tank of the No. 5 Petroleum Plant in Jinxi, Liaoning Province (now Huludao City) was put into operation, it was found that the roof of the asphalt linoleum of "three felts and four oils" was bulging in a large area, and caused serious water leakage. The large diameter of the bubble (also known as the bubble) can reach 200~300mm, and the small one is about 20~30mm, and the size of the bubble is connected in pieces, and the area reaches about 5% of the entire roof. After dissecting the bubbling, it can be seen that the bubbling is honeycomb-shaped, and the marble (i.e., the asphalt cementing material) is drawn into a thin wall; The larger the bubbling, the higher the "honeycomb wall" and even being pulled off. The "honeycomb-shaped" base layer is sometimes with small white spots, sometimes dark gray, and condensation droplets. According to the preliminary analysis, the main reason for the drum is that the crude oil stored in the tank must be melted under the action of steam above 55°C, and then sent to the oil pipeline. The roof slag insulation layer contains a large amount of water, and when it is affected by the temperature of the crude oil in the tank, the volume expands and bubbles are formed.
Later, the author observed many times that around the hole wall of the incoming (outgoing) crude oil pipeline on the roof, "hot gas" came out from time to time due to contact with the air, so there were few bubbling bubbles similar to the series of patches in this area. This peculiar phenomenon caused the author to think deeply, and thus started the arduous process of research on "roof exhaust structure".
At the same time, we also found in other roofing projects that the roof surface temperature is as high as 60 °C or more due to the influence of solar radiation heat in summer, and the volume expansion of the roof insulation layer due to the presence of moisture causes the membrane to bulge, and with the temperature change, the bubbling repeatedly appears and gradually expands, and finally causes roof cracking and leakage.
Building physics tells us that the maximum tension value of saturated water vapor is 0.61 kPa when the air temperature is 0 °C, and when the air temperature rises to 40 °C, this value is 7.38 kPa, which is more than ten times higher. Foreign studies have also shown that when the temperature on the roof is 60 °C, the partial pressure of steam inside the roof can reach 4.9MPa. The above values are enough to cause all kinds of membranes to bulge and break, resulting in roof cracking and leakage. This is a scientific explanation for the destruction of solid substances after the excess moisture inside the roof base layer is "vaporized" under the action of temperature; It is done "naturally" from the inside out, over and over again, through artificial heat sources or solar radiant heat. In order to solve this problem, we selected several projects for experiments at that time, and the main measures were to master the weather forecast and reduce the moisture inside the roof; Improve the quality of coil paving and improve the adhesion between coil and base layer. The paper "Strengthening Scientific Experiments, Strict Operating Procedures, and Breaking Through the Roof Waterproofing Barrier on the Basis of Quality Assurance" summarized by this was exchanged at the construction technology academic conference held in Dalian by the Civil Engineering and Architecture Society of the Three Northeast Provinces in July 1964.
At this meeting, Shi Jiayu, chief engineer of the Design Department of the Ministry of Construction Engineering, and Gu Pengcheng, chief engineer of the Beijing Municipal Urban Planning Administration, made academic speeches at the conference. Mr. Shi's speech quoted Mao Zedong in the "Theory of Contradiction" said: "materialist dialectics believes that external causes are the conditions of change, internal causes are the basis of change, and external causes act through internal causes", and pointed out that in scientific experiments, we should follow the method of "removing the false and retaining the true, removing the rough and extracting the fine, from the surface and the inside, from this to the other", so that the research on roof waterproofing is on the right track. At the same time, based on the experience gained in various places, he formally proposed that the roof waterproofing should adopt the guidelines of "adapting to the place and engineering conditions, preventing and draining at the same time, and combining resistance and prevention".
Mr. Gu's speech took Beijing's 1959 National Day "Top Ten" gift project as an example, and combined with the Ministry of Construction issued in May 1964 "roof concrete waterproof design technical measures (trial draft)", "roof membrane waterproof design technical measures (trial draft)" and "underground building waterproof design technical measures (trial draft)" was explained. Their speeches were commanding from a commanding height, affirming the achievements and pointing out the direction of future research. Soon after the meeting, the author wrote to Mr. Gu for advice on some problems in the pilot project and practice, and he once again emphasized that in addition to reducing water use during roof construction, he also suggested that "all nodes should be rigid and flexible to facilitate adaptation". The word "change" made the author suddenly enlightened, and also pointed out the direction of future research on "roof exhaust structure". Due to the interference of the "Four Cleanups" and the "Cultural Revolution", this research work was interrupted for a time.
2. "Exhaust steam" decompresses, and the bubbling quietly disappears
In 1970, when the military was under control, the author had the opportunity to restart the research on roof waterproofing in the "3013" project (national defense project) in Bishan County, Sichuan Province (now part of Chongqing City). In these projects, the practice of reserving the exhaust duct in the roof insulation layer and leveling layer, and setting up the exhaust hole in the roof, cornice and other parts, supplemented by the reform of the membrane paving process, changes the bottom coil close paste to point paving, strip paving or empty paving, and finally makes the research of "roof exhaust structure" (also known as "exhaust roof") achieve initial results.
The exhaust steam structure of the roof and the internal and external ventilation makes the water vapor discharge have a way out, effectively reduces the peak value of the steam partial pressure, reduces the pressure of "exhaust steam", and eliminates the internal factors caused by bubbling; The innovative process of paving multi-layer membrane (also known as laminated membrane) supplemented by "detaching the bottom coil and sticking the surface coil closely" is not only conducive to the rapid discharge of excess water inside the roof, but also can reduce many problems such as cracking, leakage and aging of the coil caused by huge temperature stress. The paper "The Causes of Bubbles in Membrane Waterproof Roof and Its Improvement Opinions", which was written by the author to introduce the above-mentioned innovative results, was first published in the fourth issue of the journal "Construction Technology Newsletter - Construction Engineering" sponsored by the China Academy of Building Research in 1972.
Later, the author promoted the use of this design technology in tens of thousands of square meters of roofing projects such as Chongqing 479 Factory and Sichuan Vinylon Factory, focusing on the standard design and effect test of exhaust holes (roads). A series of research results on the scientific principles of exhaust roofing and related structures were published in relevant magazines and the author's personal monograph around the 80s of the last century, among which the article "Practical Effect and Analysis of Exhaust Roofing" (published in Building Technology, No. 6, 1997) won the first National Journal Award for outstanding papers. Roof exhaust structure, as shown in Figure 1-3.
Fig.1. Exhaust duct practice
Fig.2. Linoleum laying method at the bottom layer of exhaust roof
Fig.3. Various construction methods of exhaust roof
In order to understand the application effect of the roof exhaust structure, in 1974, sampling inspection holes were set up on the 68,000 square meters of steam exhaust roof in the spinning workshop of Sichuan Vinylon Factory. The test results after one year show that the water content of cement expanded vermiculite in the insulation layer of each part is relatively reduced: the ridge part is reduced by about 35%, the middle of the roof is reduced by about 33%, and the cornice is reduced by about 25%. This roof waterproofing application technology researched by the mainland has reached the world's advanced level at that time (early 70s of the last century). However, compared with similar "breathing roofs" in foreign countries (i.e., building plastic drainage panels are set in the insulated roof to form a pressure balance layer), the vapor exhaust effect is more direct, significant, and long-lasting [1].
On the contrary, if there is no exhaust structure in the closed insulation or thermal insulation layer (including slope finding layer), the bulging, cracking and leakage of the waterproof layer will come unexpectedly. In October 1990, the newly built Wenzhou Airport terminal building had serious leakage due to serious leakage due to the lack of exhaust structure. Soon after the acceptance of the project, it was found that the coil was bubbling in pieces, and some of the local bulges reached 70~80mm, and the whole arm could be stretched into the base layer, which was really shocking (Figure 4). The author was invited to appraise the project and put forward a rectification and maintenance plan, so that this quality accident could be satisfactorily resolved.
Fig.4 The waterproof layer bubbles and bursts due to the large amount of water contained in the insulation layer
It is worth pointing out that today it is meaningful for us to re-examine the effect of exhaust roofing and further understand the profound philosophical ideas in it. "The language of heaven, the way of things", it is in line with the concept of "ventilation up and down" of Hanwa roof structure more than 2,000 years ago. It correctly handles the balance between the sky (wind, rain, cold and heat and other natural phenomena), the ground (how to vaporize and escape excess water in roof construction), and people (living functions), so that many complex technical problems are simplified into the scientific structure of "Taoism and Nature", and finally achieve the integration and harmonious coexistence of man and heaven and earth.
3. Analysis of the relevant provisions of the specification
According to the author's suggestion, the research results of exhaust roofing, which is mainly aimed at the design of multi-layer coils, have been included in the Code for Construction and Acceptance of Roofing Engineering (GBJ207-83) and the Technical Code for Roofing Engineering (GB50207-94), which have been widely used in the country and have achieved good technical, economic and social benefits.
In addition, the use effect of the exhaust structure in the new synthetic polymer single-layer membrane roof is of great concern to the industry. The following examples are compelling. In January and February 1995, the construction of Shanghai Songjiang Jianwu Electric Appliance Factory main factory housing project, the construction area of 10,000 square meters, the thickness of 1.2mm single-layer chlorinated polyethylene-rubber blended membrane, and according to the roof area of each half of the two different membrane paving methods, the results found that the roof constructed by the empty paving method, the membrane did not see bubbling and cracking. In the half of the roof constructed by the empty paving method, considering the weak link at the seam of the membrane, an additional waterproof membrane strip was added to the joint for the sake of safety. In addition to the common surface cracks corresponding to the cracks in the base layer, two different new cracks appeared on the half of the roof that was paved with full adhesion (Fig. 5-8), one was a regular crack at the lap joint of the coil, and the other was a regular crack at the cavity of the exhaust duct (Fig. 5-8), and then the roof was seriously leaked and forced to be repaired [2].
With the increasing variety of new waterproof materials, how to explain these new cracks that people have not recognized in the past is a new topic worthy of attention. The author believes that only through the process of experimental research and re-practice can we obtain correct conclusions, and there is no other shortcut.
Later, the test further confirmed that if the synthetic polymer waterproofing membrane is very firmly bonded with the base layer when paving, then its characteristics of high tensile strength, large elongation and strong anti-deformation ability will not be brought into play. Therefore, this kind of material should be paved with strip sticking or point sticking, such as when there is a heavy protective layer in the design structure, it can be used strip sticking, spot sticking or empty paving method. By adjusting the construction method, the above-mentioned project quality problems can be easily solved.
Fig.5 Example of cracking in the building surface of the main factory of Shanghai Songjiang Jianwu Electric Appliance Factory
Fig.6. Irregular cracks on the surface of the coil
Fig.7 There are regular cracks in the lap joints of the coil
Fig.8 There are regular cracks in the coil at the exhaust duct cavity
Finally, it is emphasized that the current GB50345-2012 specification follows the relevant provisions of the roof exhaust structure in Article 4.4.5, and points out in the description of the article: "The design of the roof exhaust structure is a technical measure for the membrane roof where the closed insulation layer is difficult to dry", while affirming the exhaust effect, it ignores the influence of different paving methods of the membrane (such as whether it is close to the base layer) on the exhaust effect and related quality; Many single-layer membrane roofs that have been constructed have also confirmed that if the membrane paving method is improper, cracking will occur, which will affect the reliability and durability of waterproofing and other quality problems.
The author is convinced that the research topic of roof "exhaust" has infinite vitality. There are indeed many articles that can be done on how to make good use of this exhaust structure that meets the requirements of green building and waterproofing, correctly understand the meaning and spirit of the code provisions, and combine the existing thermal insulation and waterproof new products, and put forward more scientific design and construction methods through more experiments and engineering practices.
2. How?
Regarding the question of how to do the roof exhaust pipe, we will take a look at the excellent engineering practices based on the quality standardization practices of China Construction Eighth Bureau and the relevant specifications and requirements. The "Technical Code for Roofing Engineering" GB50345 design of roof exhaust structure shall comply with the following provisions:
1. The separator joint set up by the leveling layer can double as the exhaust channel, and the width of the exhaust duct should be 40mm.
2. The exhaust duct should be vertically and horizontally connected, and should be connected with the atmospheric exhaust hole, which can be located under the cornice or at the intersection of the vertical and horizontal exhaust duct.
3. The longitudinal and horizontal spacing of the exhaust duct should be 6m, and a steam exhaust hole should be set up every 36 square meters of the roof area
It should be waterproofed.
4. Plastic plates with fulcrums can also be laid under the insulation layer.
01 Exhaust pipes are clearly installed
Exhaust pipe typesetting→ exhaust pipe, exhaust hole processing→ exhaust pipe installation and fixing→ roof construction to surface layer → pier construction→ gluing.
1. According to the roof typesetting, the exhaust pipe (road) is set in the insulation layer of the lattice joint, and it is advisable to use the method of burying PVC (or other materials) pipe punching and exhausting.
2. The exhaust pipe is arranged at the vertical and horizontal intersection of the lattice joint, and should be located at the higher part of the roof elevation.
3. The exhaust pipe is rooted in the slope layer (insulation layer) and other water-absorbing materials, and the periphery of the buried pipe wall should be perforated and wound with fiber cloth to prevent blockage and ensure smooth exhaust.
4. The height of the waterproof end of the exhaust pipe is greater than 250mm, and the clamp should be fixed firmly and the end should be tight.
5. Circular or polygonal pier protection, with a height greater than 250mm, will protect the waterproof end.
Schematic diagram of exhaust pipe and pier section of open set
Example diagram of stainless steel exhaust pipe and pier guard
Example diagram of PVC exhaust pipe and pier protection
Example diagram of stone exhaust pipe and pier protection
The exhaust pipes should be in a line and in the center of the lattice seam, with the same height, smooth gluing, and consistent width.
02 Concealed exhaust holes
The bleed pipe is left → exhaust hole is installed → glued.
1. The PVC bleed pipe buried in the insulation layer at the roof grid is directly led to the side of the parapet wall, smoke exhaust (air) duct or other roof walls.
2. The exhaust hole should be located in the middle of the lattice joint, and the height from the roof should be greater than 350mm and 50mm higher than the ridge.
Concealed exhaust vents and logos
Schematic diagram of the section of the concealed exhaust hole
Example diagram of buried vents
The installation is firm, the exhaust is smooth, and the gluing is smooth.
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