planning and design of sewage

PLANNING AND

DESIGN OF

SEWAGE SYSTEMS

VITUS BERING DANMARK Planning and design of sewage systems

Table of contents

PREFACE ........................................................................................................................................................ 3

DESIGN .......................................................................................................................................................... 4 CHECK LIST BY ARRANGEMENT OF SEWAGE SYSTEMS ................................................................................... 4 ARRANGEMENT OF HEIGHT CONDITIONS........................................................................................................ 5 THE PLANE PIPE LAYOUT................................................................................................................................ 6 DRAIN IN STREET AREA.................................................................................................................................. 6 ...................................................................................................................................................................... 7

PLACING OF PIPES ...................................................................................................................................... 8 ARRANGEMENT IN RELATION TO FOUNDATIONS ............................................................................................ 8 PIPES CROSSING FOUNDATION........................................................................................................................ 9

SPECIAL DEPTH DEMANDS .................................................................................................................... 10 FROSTHENSYN ............................................................................................................................................. 10 TRAFFIC CONSIDERATION ............................................................................................................................ 10 CONSIDERATIONS FOR OTHER SYSTEMS....................................................................................................... 10

LOSS OF HEIGHT ....................................................................................................................................... 11 BY DRAIN PLACES ........................................................................................................................................ 11

CLEANING.................................................................................................................................................... 12 CODE OF PRACTICE REQUIREMENTS............................................................................................................. 12 IMPROVEMENT OF CLEANING ACCESSES ...................................................................................................... 12 ACCESSIBILITY OF CLEANING SPOTS ............................................................................................................ 13 SITING AND DISTANCE BETWEEN CLEANING SPOTS ...................................................................................... 13

CHANGE OF DIRECTION OF LYING PIPES......................................................................................... 15 CONNECTION TO LYING PIPES............................................................................................................. 16

CONNECTION OF LYING PIPES TO LYING PIPES.............................................................................................. 16 EXAMPLES OF SOLUTIONS .................................................................................................................... 17

EXTERNAL ROOF DOWNPIPE......................................................................................................................... 17 DRY PIPES .................................................................................................................................................... 17 CONNECTION OF MORE GULLYS ................................................................................................................... 17 DRAIN FROM EXTERNAL BASEMENT STEPS................................................................................................... 18

PREPARATION OF DRAIN PROJECTS.................................................................................................. 19 SEWER PLANS .............................................................................................................................................. 19 PURPOSE ...................................................................................................................................................... 19 DRAWING BASIS........................................................................................................................................... 19

EXAMPLE OF SEWER PLAN.................................................................................................................... 20 SIGNATURES FOR SEWER PLANS......................................................................................................... 22


Preface This publication “Planning and design of sewage systems” is worked out to act as a refer-ence book in connection with design of sewer plans. The publication first of all applies to constructing architect students, because the material is chosen from all the questions, which arise in connection with the daily work in the con-structing architect study. Great importance is attached to short descriptions and belonging illustrations, so that the publication can be used as reference during the work making a rational sewage system. The text is not new, as all text and illustrations are chosen from SBI-direction 185, Drain-age installations. 2. edition, 1997.

Vitus Bering Danmark April 2004 Jens Peder Pedersen


Arrangement of the sewage system

Design By design all conditions concerning drainage installations are determined so detailed; that the installation is unambiguous determined and can be made according to the project mate-rial. The project has to explain all conditions concerning the building regulations, environ-mental legislation, codes of practice etc. and the special conditions concerning the topical building. The design should among other things determine the installation in connection with the buildings and their surroundings, dimensions and slope and state specifications for all components and joining methods.

Check list by arrangement of sewage systems 1. Procure all necessary information e.g.:

• a reasonable good drawing material

• information about all drain places and their use and ventilation conditions

• information about existence of harmful substances

• information about main sewer and connection conditions

• information about prohibition, easements, building lines, etc.

2. Make decisions about special components and systems, e.g perimeter drain, and exam-ine placing possibilities and levels etc.

3. Choose experimentally a connection place.

4. Examine the slope conditions

• where is the most dangerous point?

• which slope can be used?

• how big loss of height should be noticed by the drain places, in pipes and components and by connection?

• will there be special demands for depth, e.g for extension?

• do you have damming in main sewer, and which safety heights should be fulfilled?

• is the available slope enough?

5. Choose if necessary another connection place.

6. Mahe decisions about pumping:

• but only, if it is absolute unavoidable.

• remember, that pumping could also be necessary for perimeter drain.

7. Sketch a pipe layout (track):

• take care of foundations and other building components.

• take care of other pipes and systems.


• take care of systems on neighbour property.

8. Arrange slope conditions:

• try to obtain plenty, uniform slopes.

• avoid big slope changes.

• consider savings in digging depths by downlead and similar.

9. Make use of available materials – but also notice the restrictions, they could present.

10. Arrange possible drain systems and their connections.

11. Be sure, that the system is easy to clean, where this is important.

12. Be sure, that you have easy access to the places, where it is needed because of inspec-tion and draining etc.

13. Examine, if all pipe crossings are possible.

Arrangement of height conditions The most dangerous point in a drain installation is the one, which is most difficult to drain, either because it is placed deep or because it is placed far away. The drain installation should as well as possible be made without pumping. It is therefore decisive, if the avail-able height difference between the connection level and the most dangerous point is suffi-cient, so that the pipes can be laid with minimum slope. Arrangement of slope If the available slope is plenty, the slope should be shared out from the most dangerous point to the connection point. The most simple is to place the pipe straight between the two points. This solution is very often the most expensive, because the digging work will be bigger, see figure 1. Figure 1. Straight pipe between floor drain and street sewer (A) causes a deeper well and and extra digging work corresponding the hatched area.


In practice it is inconvenient with a lot of slope changes and also changes of direction in a pipe. Therefore as a rule it is very often chosen to place the pipes straight passing more branches and only changing slope in wells.

The plane pipe layout

The economi is of course a main factor by arrangement of a drain system. This means among other things, that the pipe length should be as short as possible and the pipe layout as simple as possible. An assignment can almost always be solved in many ways. Still certain main principles are common:

• the most important pipes should be led the shortest possible way to main sewer pipes

• the layout should be in a way, that the accumulating pipes are led tight past the most important installation groups

• the cleaning possibilities for the accumulating pipes should be good and the clean-ing access easy accessible

• the pipe system should as well as possible be ventilated. Inlet The design is started by determining all inlet places in the system, that is all drain objects, floor drains, standing pipes and roof downpipes and terrain drains etc. furthermore it is important to prove, where the system is ventilated or can be ventilated. Some inlets are quite firm, e.g. drain objects as wc, while other inlets can be moved a little, if it causes better solutions. This will often involve floor drains and gullys. In the interests of accessibility the pipes should be led outside the building, as direct as possible. This is not an absolute demand, if it makes the drain system unreasonable expen-sive, see figure 2 next page.

Drain in street area Rain water pipes: In principle all drains (except for service pipes) should be kept inside private property, this is behind property-line and also behind building line and etc. Where a building is placed up to property-line along street, and permission is given to place roof downpipes and open light shafts in footpath outside property-line, it will nor-mally also be permitted to lead footpath pipes along the building and to place gullys here. Very often this area is called “light shaft zone”, and is about 0,5 m. Even if there are no light shafts – and in this area, perimeter drains, rain water pipes and gullys can be placed here. On the contrary waste water pipes must not be led here, and also the same for floor drains led to a gully. Cleaning wells: Private cleaning wells are normally not allowed in the street area.


Figure 2. Example of pipe layout in connection with strip building.


Placing of pipes In figure 3 are shown some recommend distances between building components and pipe system outside the building.

Figure 3. Placing of pipes outside the building and recommended distances to bilding etc. a states normal distance to building, but it can be both smaller and bigger, depending of

other installations, neighbour site and foundations. b states a reasonable smallest distance to building overhang – practically to give space

for digging-up. c states normal distance between pipes in separate system, still depending of placing of

wells.

Arrangement in relation to foundations Drain installations should normally be placed in a way, that the foundation of a building is not inadmissibly reduced. Guidelines for this are stated in Code of practice for fuondation, DS 415. It is worth noting that concept buildings also include pipes for e.g. water, gas and district heating and other drain pipes. Given that according to the Code of Practice, we talk about modified foundation class (single-family houses), you can follow the guidelines in figure 4. Temporary excavations along existing foundations must not be lower than the boundary surfaces, shown in figure 4. If the limitations in the depth can not be respected, the pipes must be laid in a bigger distance from the foundations, or the foundation must be led deeper down. The first solution is normally the cheapest. See figure 4 next page.


Figure 4.Boundary surfaces for excavations along foundations in clay soil.

Pipes crossing foundation Pipes, which are crossing foundations, must not be casted in the foundations, and they must not be placed below the lower edge of the foundation. The pipes are led through a recess with 50-100 mm air gap around the pipes. If pipes cross below the lower edge of the foundation, foundation downleads have to be made, as shown in figures 5 and 6.

Figure 5. Foundation downlead for pipes, which cross a foundation below the lower edge of the foundation. Figure 6. Stepping in foundation downlead by deep pipes.


Special depth demands

Frost regards To avoid the water in a pipe to freeze, the pipe should be at least 0,75 m below terrain, measured to internal pipe bottom level. Same depth for water level in gullys. In more cases can smaller depths be used: 1. Dry pipes for roof water 2. Water traps or gullys in basement steps etc. 3. Insulated pipes 4. Drain pipes by heated buildings Dry pipes are roof water pipes or pipes from cheat wells before gully or other permanent water filled part. These pipes can be placed as high as the conditions allow, e.g. in a depth of 0,3 – 0,4 m close to buildings, where ground milling will not be done. Water traps in protected basement steps can be placed with water trap in normal depth, which means about 250 mm below floor. in gullys in basement steps the distance from grating to water surface should be 400 mm. This is based on experience. Strings around basement steps are led 0,6 m down below floor level, which give access for ground heat form below. Furthermore drains in smaller basements will get a heat gain from neighbour-ing heated basement rooms. If the location is exposed, the drain can be made as a bending, which is led to a gully outside the basement steps. Pipes below building can be placed in very small depth, provided that they are not exposed for frost. The same also below crawlways, but it depends on the construction of the crawl-way and the location and insulation. Insulation of frost exposed pipes can be made with plates of insulation material above and around the pipes. Drain pipes, which are placed near to a heated building, should be frost safe with a depth of 0,6 m.

Traffic consideration A depth of 0,75 m will not always be defensible below areas with traffic. For each pipe type and material information must be found in catalogues about permissible smallest depth regarding traffic load, or special calculations of strength must be made.

Considerations for other systems Crossing of other pipes in the ground can, if the drain pipe is plaved lowest, cause lower levels than normal.


Loss of height

By drain places For drains in floor or by ground deck special form pieces are normally used, e.g. bendings or water traps, which cause a loss of height compared with the floor level. Normally you try to obtain that the muffs of lying ground pipes are free of the floor construction. A loss of height of 250 mm will in most cases be sufficient, but both bigger and smaller losses of height can be actual depending on the form pieces that are used, see figure 7. Figure 7. Loss of height below level of basement floor (GK) is calculated to the course level (L): a By a duckfoot bending can normally be calculated with 250 mm, when the duckfoot

bending is placed with lower edge of coupling in floor level. b By a floor drain followed by a water trap should be calculated with at least 250 mm

and often more, depending of the used parts. c By a floor drain with build in water trap followed by a bending, the loss of height can

be from 250 - 400 mm. d A pipe always has to be laid so deep below floor, that its coupling will not be embed-

ded in concrete, especially with heavy traffic on the floor.


Cleaning

Code of practice requirements The Code of Practice makes demands about that all parts of the drain installation can ob-tain easy cleaning. The cleaning should be made without essential inconvenience and without risk of damage and health risk. The cleaning accesses should be easy to localize, easy accessible and easy to serve. The Code of Practice does not make specific demands about number or placement of the cleaning accesses, and by the planning you can in that way take into consideration, which cleaning methods are used. No matter the cleaning pos-sibilities, the installation should be made in a way, that the risk for settlement is small.

Improvement of cleaning accesses Cleaning accesses can be of many different constructions, and in the following there are mentioned som of the most common. Manholes Manholes are the traditional cleaning access for pipes in ground. A manhole is by “Ar-bejdstilsynet” defined as a well with an internal diameter of 1,25 m and an access opening of at least 0,6 m. In connection with one- and two family houses, linked houses and alike wells with a diameter of 1,00 m can be used as manholes. Cleaning- and inspection wells in plastic VA-approved cleaning- and inspection wells in plastic can be used as cleaning access. The diameter is normally 300 – 400 mm, and the depth should with the present systems not exceed 4 m for the sake of the strength. Cleaning spots Cleaning spots are form pieces with a removable cover. Cleaning spots take part of the VA-approved drain systems. The cover can be secured with screws, bolts with thread or in another way. See figures 8 and 9. Figure 8. Inspection piece of plastic Figure 9. Inspection piece of cast iron and stainless steel


Cleaning branch pipes Cleaning branch pipes can be made of ordinary branch pipes, where a not-used branch is provided with a removable cover (end plate for muff). In figure 10 are shown examples of cleaning brance pipes placed in ground. Similar constructions can be used in buildings. Figure 10. Inspection branch pipe. A og B can with tight cover be used in the open air, whith no traffic load. C og D can be used indoor.

Accessibility of cleaning spots Cleaning accesses should be easy to localize. They should be clearly indicated and if pos-sible with the dimensions marked in the drawing, and they should be easy to find, which means placed visible. Covers on manholes and cleaning wells should have measures in proportion to buildings or other fixed terrain objects. The covers should in garden areas be raised so much above terrain, that they are not hidden by soil or plantation. There should be easy access to the cleaning accesses. They should not be placed in locked rooms, store rooms and similar places. There should be sufficient free height and free area for transport of cleaning tools, and so that the cleaning work can be done in a reasonable way. Placing of cleaning accesses in crawl spaces can normally be accepted. The cleaning work can cause pollution etc. of the surroundings, and this should be respected by the placing of the cleaning accesses. Cleaning accesses must not be placed in living rooms or in kitchens in restaurants, store rooms for food and similar, where health risk can arise. Pipes, which are shared for more dwellings, should be cleaned from cleaning accesses, which are placed inside every single dwelling.

Siting and distance between cleaning spots Cleaning accesses should be placed suitable from the design of the part of the drain sys-tem, they shall serve. The best cleaning conditions you get, when the pipes, that are most exposed for chocking, e.g. pipes from wc and kitchen sink, are led directly to cleaning well. See figure 11.


Figure 11. Pipes, that are most exposed for blocking, should be led directly to cleaning well. A: Good solution. B: Bad solution. The number of changes of direction in pipes between two cleaning accesses should be lim-ited. Normally it will be acceptable, that you have two 45° bendings and a duckfoot bend-ing between two cleaning accesses. By connection of branch pipes to an accumulating pipe, the length of the branch pipe should not exceed 10-15 meter. The number of and the size of the changes of direction should be as small as possible, e.g. max. 45° for pipes with more installation objects, and max. 90° for pipes with one installation object, see figure 12. Branch pipes are difficult to clean, and changes of direction increase the risk for blocking Figure 12. Limitation of length and number of changes of direction of branch pipe. The distance between two cleaning accesses can be adjusted according to the chosen clean-ing method. By normal drain installations, where it could be necessary to clean with clean-ing-split, the cleaning accesses in wastewater pipes should be placed the following places: • In pipes in floor or below ground deck with a distance of at highest 20 m. • By change between standing and lying accumulating pipes in building. • After total change of direction of 90° no matter the distance to the next cleaning access. • In ground outside the building, so that the distance between the cleaning accesses is at

highest 40 m. Longer distances can be accepted, if it can be shown, that normal used cleaning tools can be used. The distance between the last cleaning access in building and the first in ground should at highest be 20 m.


• In building by change from pipe in building to pipe in ground. Cleaning of rain water pipes is not so required. Still, cleaning accesses should be used in rain water installations, so that the service pipe can be cleaned.

Change of direction of lying pipes In pipes, which are connected to one installation object, form pieces with a change of di-rection of at highest 88°, can be used. See figure 13. When sharp changes of direction increase the risk of blocking, you should be careful with pipes, that are very exposed for blocking, e.g. pipes from wc and kitchen sink. The bigger radius the bending has, the more the risk for blocking is reduced. Therefore only 88° bend-ings with big radius should be used by change of directiopn in coupling pipes. Figure 13. Change of direction of 88o can be used for pipes, which are only connected to one installation object. A: Bad solution. B: Good solution. In pipes, where more than one installation object is connected, you should use bendings, which are at highest 45°. Is the change of direction 90°, a straight piece of pipe of at least 0,3 m should be insert between the bendings, see figure 14. Figure 14. By changes of direction of 90° should be used two 45° bendings with a straight piece of 0,3 m between the bendings. Changes of direction of more than 90° should be made in manholes. Special form pieces can be used on those conditions, which are stated in the VA-approval.


Connection to lying pipes

Connection of lying pipes to lying pipes Connection is mainly made with VA-approved form pieces in cleaning- and inspection wells or in manholes. Figure 15. Double branch pipes should not be used in lying pipes. By connection in cleaning- and inspection wells built on the spot are used connection angles, which are smaller than 60°, and opposite connections should be displaced in proportion to each other, so that flooding is avoided, see figure 16. Figure 16. In wells build up on the spot, opposite connections should be displaced com-pared to each other, and the connection angles have to be smaller than 60°.


Examples of solutions

External roof downpipe

Figure 17. Roof downpipe connection to gully

Dry pipes Figure 18. Dry pipes to the same gully

Connection of more gullys Figure 19. Pipe layout from more gullys


Drain from external basement steps Figure 20. Floor drain without water trap led to gully outside the basement steps. Good solution. Figure 21. Floor drain with water trap led directly to the sewer system. Less good solu-tion.


Preparation of drain projects

Sewer plans A building work, and also a drain work, must not be started without permission from the local authorities. To acquire permission, an application has to be sent in, according to the building regulations. This application has to be attended by a drawing, which shows possi-ble existing and/or designed drain systems. This is called a sewer plan. Sewer plans can contain information about as well installations in building as in ground, which means both sanitary work and sewer work.

Purpose A sewer plan has more purposes. As mentioned it should:

1. Form the basis of evaluation of the legality of the project compared with valid laws and codes of practices and other provisions.

Furthermore it should: 2. Form the basis of material counting and evaluation of different work contributions,

which means pricing and arrangement of timetable. 3. Form the basis of execution of the work. 4. Form the basis of operation- and maintenance arrangements and future changes.

The sewer plan is very often supplemented with e.g. specifications and conditions etc., es-pecially in the interests of point 2 and 3. This can be reasonable in purpose of expressing special wishes or demands. But it is needless, if it is only a rattling off of the laws and codes, which already are valid.

Drawing basis The natural basis for a sewer plan is a building drawing (plan drawing) of the lowest sto-rey, e.g. a basement plan. By bigger buildings with complicated foundations if possible a foundation plan. The drawing basis should also include necessary cross sections, among other things to be able to evaluate the proportions of the foundations. Furthermore a site plan showing property-lines and adjoining roads is very often necessary to illustrate con-nections to main sewer pipes etc. Building drawings should contain sufficient informations about levels on terrain and building parts (floor levels etc.). Drain installations can be divided into internal installations (in building) and installations in ground. By tradition these two domains are handed over to authorized professions: the plumber and the sewer contractor. The border between these two professions is as a rule the change by the floor against ground. A drain project will very often contain the whole drain installation. Internal pipes are drawn in the building drawings, but is very often detailed in diagrams of the drain installa-tion, see figure 22 – while pipes in ground are drawn in the basement- or foundation plan.


Figure 22. Diagram of drainage installations

Example of sewer plan A sewer plan should contain so many superscriptions and measurers etc., that the stated systems can be built without further informations except for such that as usual are men-tioned in a description (material and lying demands etc.). In figure 23 is shown an example of a sewer plan. The superscriptions in the sewer plan is first of all distances, measures, levels, dimensions, slopes and materials etc., and itn is of course possible to include further more detailes. Still the drawing can very easy loose som clearness, if it is overloaded with superscriptions. The extent of the superscriptions should be limited to the absolute neces-sary. Levels, which can be calculated without trouble from already given information, should be avoided. Frequent superscriptions of common occurrence can be given in a uni-fying information, e.g.: ”All abstract pipes are 110 mm PVC, which are laid with at least 20 o/oo”. Shortenings (of materials, objects etc.) are used as much as possible. Superscriptions should be made with readable writing, so that it is clear, where it belongs. See example of a sewer plan, figure 23 in next page.


Figure 23. Example of sewer plan.


Signatures for sewer plans Signature Remarks

New pipes

Separate system Waste water system (solid line) Rain water system (interrupted line) Heavy line.

Perimeter drain (interrupted line with dots) Heavy line.

Crossing pipes The line for the lowest pipe is interrupted. Bottom level should be insert parallel with the pipe, it belongs to.

Water trap.

Existing pipes

Existing systems (short interrupted lines, no matter which system) Thin line.

Existing system, which is dismantled. Cork. = Corking.

Wells and intercepting traps etc.

Cleaning- and inspection wells with bot-tom trenches. Diameter of upleading pipe is 315 mm. Bottom level 19,08 is well centre.

Manhole with bottom trenches and at-tached rain water inlet (plasher). Diameter 1,25 m (cone- and cover diameter are normally not stated). Bottom level 17,20 is well centre. Levels for pipe lead-in can if necessary be stated.


Signature Remarks

Wells and intercepting traps etc.

Gully (circular) with water trap and tight cover. With sand- and catch pit. Diameter 300 mm. Level to water trap (water level) 9,28. Bottom level for inlet 10,05.

Gully (circular) with water trap and and grating for surface inlet. With sand- and catch pit. Diameter 300 mm. Level for water surface 10,45.

Roof downpipe gully (gully with bending) with water trap and cover. With sand- and catch pit. Diameter 200 mm. Level for water surface 14,50.

Floor drain with circular drain basin (without water trap). Floor drain with square drain basin (with water trap). Connection diameter should be stated. Level for water surface 9,85.

planning and design of sewage

Documents

arrangement of sewage

design of sewage systems

placing of pipes

drain places

loss of height

pipes crossing foundation

table of contents preface

check list