Sanitary Drainage in Buildings
André Henrique Patrício Botica
Dissertation for obtaining the master's degree in
Military Engineering
Jury President:
Professor Doutor Jorge Manuel Caliço Lopes de Brito
Supervisor:
Professor Doutor Albano Luís Rebelo da Silva Neves e Sousa Professora Doutora Maria Cristina de Oliveira Matos Silva
Examiners:
Professora Doutora Filipa Maria Santos Ferreira Major de Engenharia Mestre João Carlos Martins Rei
October 2012
1
Introduction
Although people have started to drain sanitary wastewaters at least five thousand years ago, the evolution of such drainage systems have been slow, mainly in buildings. The drainage systems used nowadays are the result of developments occurred between the beginning of the 19th century and the middle of the 20th century. Since then, quality has been assured by building codes and standards, which often offer simplified design methods to be used by technicians. Unfortunately, as often happens, these simplifications, which, in the short term, are useful to ensure that most building drainage systems are properly designed and installed, at the long term may contribute to hide theoretical fundamentals, and eventually to an inadequate technical and scientific background of technicians having to deal with more complex buildings. Actually, adequate design of building drainage systems of sanitary wastewaters requires a comprehensive knowledge not only of technical requirements but also of the available technologies and design methodologies. This work aims to gather the information required for designing sanitary wastewater drainage systems in buildings. Building codes, regulations and technical standards will be considered, as well as other general quality recommendations. Design methods considered in Portuguese regulations will be compared with methods considered in other codes, such as:
the European standard, which must be adopted by countries in the European Union although adapted to specific national legislation and standards;
the Brazilian standard, which is based in the American model, thus causing some difficulties to Portuguese professionals who need to practise in Brazil.
2
Sanitary wastewater drainage systems in buildings
The drainage network of sanitary wastewater is used to gather sewage and then conduct it to the public drainage system, where sewage will flow towards its final destination, i.e., a wastewater treatment plant. The process of designing wastewater drainage systems can be divided into four phases. The first phase aims to gather information about the building, such as architectural or structural restrictions, and then to identify optimal locations for vertical pipes, which are those where conflicts with other building services are avoided. At this stage, also the need for elevation systems of wastewater collected at lower levels should be assessed. In the second phase, the main route of the drainage system is preliminarily defined. The system will be optimized during subsequent stages of the project as occurs in the third stage, where diameters and inclination of pipes are set. Finally, in the fourth stage, after installation of the system, actualized plans should be produced in order to ease future maintenance and inspection works.
2.1
System components
Building sanitary drainage systems include several components:
Accessories: devices, such as connections, fittings, or valves, which ensure the adequate functioning of the drainage system and allow maintenance and repairing works.
Branch discharge pipe: pipe that links the appliance producer of wastewater or the water trap to the discharge stack or drain.
Branch ventilating pipe: pipe that ensures the water seal of traps when it is not guaranteed by primary ventilation.
Discharge stack: ventilated pipe that aims the vertical downward transport of wastewater, gathering the effluents of various near horizontal discharge pipes.
Ventilating stacks: pipes that complement the primary ventilation system in discharge stacks when this is insufficient.
Drain: nearly horizontal pipe aimed to gather itself the effluent from discharge stacks and branch discharge pipes and then to conduct sewage to a new stack or the outside chamber.
Building inspection chamber: manhole located within the property limits aimed to gather the sewage of connecting drains and then to conduct it to the building drain.
Building drain: pipeline aimed to conduct all wastewaters produced in the building to the public sewer. Although this pipe is part of the public network it must be installed by the building owner. For large buildings, there can be multiple drains connected to the public sewer, but building drains gathering sewage from different buildings are not allowed.
Public sewer: pipe system which receives the effluents of different buildings and conduct them to their final destination.
2.2
Building sanitary drainage systems
The public sanitary drainage systems can be divided into four types:
Combined system, in which sanitary wastewater and rainwater drainage are provided by the same pipe;
Separated system, in which sanitary wastewater and rainwater drainage are provided by different pipes;
Mixed system, which includes the two previous systems;
Pseudo-separated system, which is a actually a separated system with exception to rainwater collected on indoor terraces and conducted to the sanitary wastewater public sewer.
Regardless the existing or projected public sanitary drainage system, sanitary wastewater and rainwater drainage in the building must be separated and flow from the building inspection chamber to the public sewer through the building drain must be driven by gravity. Inside the building, three systems for conducting waste water can be adopted:
Gravity system, where all wastewaters are collected at a level higher than that of the building drain;
Pumped system, where all wastewaters are collected at a level lower than that of the building drain thus requiring pumping to elevate them to a higher level;
Mixed system, which combines the above systems.
2.3
Installation and quality rules
In Portugal, installation of sanitary wastewater drainage systems must comply with Portuguese regulations. However, there are other quality rules which are stated in standards and books on the subject. In this work, the main rules and recommendations were gathered and then summarized into tables for each component of the drainage system. 2.3.1
Comfort
Smelling and noise must be avoided in order to assure comfort of the building occupants. Noise from drainage networks in buildings is essentially impact noise transmitted mainly by vibration of construction elements. To reduce or prevent such noise transmission, pipes and accessories must be isolated from the building structure by appropriate materials such as rubber or mineral wool. Also flexible materials such as elastic joints should be used to absorb impacts and vibration generated by sewage falling down in stacks or by direction changes in branch discharge pipes and drains. Pumps are another noise source which should be baseisolated. Gases originated in the pipes must not enter dwellings. A depth of water seal is used in traps installed in sanitary appliances or on the floor in order to comply with this requirement.
3
Designing methods
Designing of a building sanitary drainage system must take into account compliance with legal requirements, adequate performance both in terms of flow capacity and self-cleaning, and coordination with other building services, always looking for the lowest combined cost of implementation, maintenance and operation. Adequate sizing of building sanitary wastewater drainage systems is obtained after a correct definition of both the network and accessories to be installed followed by:
Calculation of flow rates;
Determination of pipe diameters and corresponding inclination, in the case of nearly horizontal pipes;
Verification of the need for ventilation auxiliary systems in order to keep water seal in traps.
Sizing of inspection chambers as well as pump groups when needed.
In this work, the design methods given in Portuguese Regulations and in the European Standard and Brazilian Standard will be analysed and compared (see section 5).
4
Materials
The importance of adequate building sanitary drainage systems is directly related to the maintenance of public health and environmental quality. Both requirements are met through appropriate drainage and its proper sizing. However, the materials used also play an important role, and should ensure:
Resistance to internal and external stresses;
Resistance to the action of ice and temperature variations;
Drainage conditions (roughness of the pipe as smooth as possible);
Resistance to abrasion;
Resistance to chemical aggression;
Dimensional reliability (reduced in diameter tolerance provided by manufacturers);
Ease of transport, installation and maintenance;
Reduced costs (material, transportation and maintenance).
The quality of the pipes and accessories used in the drainage system should be guaranteed with quality certificates of accredited entities. In general, materials used are divided into concrete, ceramic, metal or plastic. Each of these groups has subgroups according to their suitability for use in each situation. Although any material can be used, the material most often used in building sanitary wastewater drainage systems is plastic, namely PVC.
5
Case study
In order to illustrate the application of the design methods considered in Portuguese Regulations and in the applicable standards used in the European Union and Brazil, a building sanitary wastewater drainage system was designed considering a fictional building. The building, with 4 floors above the ground and 1 underground floor for parking and storerooms, is assumed to be located in a region served by a public sewer.
5.1
Solution adopted
In Figures 5.1 and 5.2 building plants are shown respectively for ground floor and for the above floors. The plants are simplified, being presented just the toilets and kitchens, which are the relevant facilities for the present work. In Figure 5.3, the drainage system of each room (kitchens at left and centre and sanitary facilities at right) is detailed. For simplicity, it is assumed that the basement level is higher than the level of the public sewer in order to allow gravity flow directly from a building inspection chamber installed in the basement.
Figure 5.3 - Kitchen (left and middle image) and WC (image from the right) pipe distribution.
Figure 5.2 – Plan of floor 1 to 3.
Figure 5.1 – Ground floor plan.
Although kitchens exhibit different layouts, their vertical alignment allows the use of only three discharge stacks as shown in Figure 5.3. Drains and building drain with respective building inspection chamber are shown in Figure 5.4.
D2
D1 D3
Figure 5.3 - Location of discharge stacks.
Figure 5.4 – Location of drains and building drain.
Figures 5.1 to 5.4 are in a simplified form not complying with standard scales and symbolic representation.
5.2
Sizing
PVC pipes were considered with a slope of 10 mm/m in the case of near horizontal pipes. For application of the European standard, systems I and II were considered. Results obtained for each component of the system are shown in the following Tables.
Table 5.1 - Flow for individual equipments Portuguese Appliance
regulation
EN 12056 I
EN
NBR
12056 II
8160
Calculation of flow rate (l/s)
NBR 8160
UHC
Toilet Bowl (Br)
1.50
2.00
1.80
0.96
6
Bath (Ba)
1.00
0.80
0.60
0.90
2
Washbasin (Lv)
0.50
0.50
0.30
0.15
1
Bidet (Bd)
0.50
0.50
0.30
0.40
1
Sink (LL)
0.50
0.80
0.60
0.25
3
Dish machine (ML)
1.00
0.80
0.60
0.30
2
1.00
0.80
0.60
0.30
3
Washing machine (MR)
Table 5.2 - Discharge diameter of individual branches
Portuguese regulation
Appliance
EN
EN
NBR
12056 I
12056 II
8160
NBR 8160 (UHC)
DN (mm) Toilet Bowl (Br)
90
90
80
100
100
Bath (Ba)
40
50
40
40
40
Washbasin (Lv)
40
40
30
40
40
Bidet (Bd)
40
40
30
40
40
Sink (LL)
50
50
50
50
50
Dish machine (ML)
50
50
50
50
50
50
50
50
50
50
Washing machine (MR)
Table 5.3 – Group discharge branch diameters Portuguese
served
1Ba+1Bd+ 1Lv
EN 12056 (SI)
regulation
Appliances
DN
EN 12056 (SII)
DN
NBR 8160
DN
NBR 8160 DN
l/s
l/s
mm
l/s
l/s
mm
l/s
l/s
mm
l/s
l/s
mm
2.00
1.59
75
1.20
1.20
75
1.45
1.45
63
1.45
1.45
50
UHC
4
Table 5.4 - Ventilating branches Portuguese
Portuguese
regulation
regulation
EN 12056
EN 12056
Secondary
Analytical
Graphical
(SI)
(SII)
ventilating branch
method
method
DN
DN
DN
DN
(mm)
(mm)
(mm)
(mm)
V1
75
75
50
50
80
75
V2
40
40
50
50
32
75
V3
40
40
50
50
32
75
NBR 8160
UHC
DN (mm)
DN mm 50
Table 5.5 – Discharge stacks without secondary ventilation Portuguese
Portuguese
regulation
regulation
Analytical
Graphical
method
method
Stack
DN
D1
D2/D3
EN 12056
EN 12056 (SI)
DN
NBR 8160
(SII)
DN
DN
DN
(l/min)
(mm)
(l/min)
(mm)
(l/min)
(mm)
(l/min)
(mm)
391.25
140
301.74
125
337.64
125
312.25
125
263.03
110
241.21
110
189.74
110
164.32
NBR 8160
(l/min)
90
(mm)
UHC
DN (mm)
Does not
Does not
check only
check only
primary
primary
ventilation
ventilation
Table 5.6 – Discharge stacks considering secondary ventilation. Portuguese
Portuguese
regulation
regulation
Analytical
Graphical
method
method
Stack
DN
EN 12056 (SI)
DN
EN 12056 (SII)
DN
NBR 8160
DN
DN
NBR 8160
UHC
DN
(l/min)
(mm)
(l/min)
(mm)
(l/min)
(mm)
(l/min)
(mm)
(l/min)
(mm)
D1
391.63
90
301.74
90
337.64
110
312.25
110
289.20
110
80
110
D2/D3
263.03
75
241.21
75
189.74
90
164.72
75
102.00
75
32
75
(mm)
Table 5.7 - Secondary ventilating stack. Portuguese
Portuguese
regulation
regulation
Vent
Analytical
Graphical
Stack
method
method
DN
EN 12056 (SI)
DN
EN 12056 (SII)
DN
NBR 8160
DN
DN
NBR 8160
UHC
DN
(l/min)
(mm)
(l/min)
(mm)
(l/min)
(mm)
(l/min)
(mm)
(l/min)
(mm)
(mm)
V1
391.63
63
301.74
63
337.64
50
312.25
50
289.20
50
80
75
V2/V3
263.03
50
241.21
50
189.74
50
164.72
50
102.00
50
32
75
Table 5.8 - Drains and building drain Drains in
Portuguese
Portuguese
buildings
regulation
regulation
EN 12056
EN 12056
and
Analytical
Graphical
(SI)
(SII)
connecting
method
method
branch
DN
DN
DN
DN
NBR 8160
DN
NBR 8160
DN
l/min
mm
l/min
mm
l/min
mm
l/min
mm
l/min
mm
l/min
mm
C1
391.25
140
301.73
125
337.64
160
337.64
125
289.20
160
80
110
C2
263.03
110
241.20
110
189.74
125
189.74
110
51.00
110
112
110
C3
559.71
140
500.19
140
431.28
160
431.28
125
391.20
200
144
110
RL
559.71
140
500.19
140
431.28
160
493.20
160
391.20
200
144
110
6
Conclusions
Despite the design methods recommended in the rules and regulations considered in this work are based on identical assumptions, simplifications can be made in order to develop quick design methods based on tables. The European standard EN 12056-2 and the Brazilian standard NBR 8160 offer such methods, although the use of alternative analytical methods is always possible. The later is used as the main calculation method in Portugal. The case study showed that design results rely heavily on discharge flow rates considered, with some differences between standards and regulations considered. Pipe sections also can exhibit significant differences according to the occupancy rates allowed. An important conclusion of this study is that Portuguese regulations lack information and detail on assuring the depth of water seal in traps. Another important conclusion is that simplified methods, such as the one presented in the Brazilian standard NBR8160, are not always conservative when compared with more detailed methods. This work has a monographic nature aimed to gathering and selecting available information on the subject of building sanitary drainage systems.
