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In most cases, sewers are made gravity-fed. This means that all drains leave on their own, under the influence of gravitational forces. But in order for them to move, the pipes must not be laid evenly, but with a slope, and with a certain one. What should be the slope of the sewer pipes and we will talk further.
What is the slope of the sewer pipe for?
Everyone has probably heard that sewer pipes must be laid with a slope, and even with certain building codes – SNiP. Why exactly? Because it is necessary that the speed of movement of wastewater through the pipes be such that water and solid particles move together.
When laying or repairing an existing sewer on my own, I often make two mistakes:
- Make the slope less than recommended. In this case, the water leaves very slowly, the pipeline section is often clogged. Even if we are talking about a bathroom, sediment accumulates in the pipes, which causes blockages. If a toilet pipe is laid with a slight slope, then, firstly, there may be problems with flushing, and secondly, the smell of decaying waste products will be added.
The sewer pipe must be laid with a certain slope - The slope of the sewer pipe is made too large. This case is no better. Water leaves quickly, and solid inclusions remain in the pipe. They rot, spread odors, and even cause clogging. In this state of affairs, the sewers have to be cleaned almost every month.
The norms specified in the SNiP are advisory in nature, but they are written based on many years of experience, so it makes sense to listen.
What should be the slope
How to understand what a pipe slope is? In SNiP, it is written in fractions – in the form of decimal dobies. It looks like this: 0,03 or 0,008. The numbers are deciphered as follows: this is the height difference between the two ends of a meter-long piece of a laid sewer pipe. The number 0,03 means that one end of the meter pipe is raised by 3 cm. Accordingly, the number 0,008 indicates that one end is raised by 0,8 cm or 8 mm.
The pipeline is usually much longer than one meter. You can calculate how much one end of it should be higher than the other by multiplying the selected slope by the length of the pipeline. For example, we will lay a sewer with a slope of 3 cm / m, its length is 25 m. This means that its far end will be lowered by 3 cm * 25 m = 75 cm.
Dependence on pipe diameter
Sewer systems are divided into internal – mounted in an apartment or house, and external – which are laid on the street. In both cases, it is necessary to maintain the required slope of the sewer pipe. When they say so, they mean the indicator recommended by sanitary standards. It depends on the diameter of the pipes used: the smaller the cross section, the greater the slope must be given.
| Sewer pipe diameter | Normal slope | The smallest allowable |
|---|---|---|
| 50 mm | 0,035 (3,5 cm) | 0,025 (2,5 cm) |
| 100 mm | 0,02 (2 cm) | 0,012 (1,2 cm) |
| 150 mm | 0,01 (1 cm) | 0,07 (7 mm) |
| 200 mm | 0,008 (0,8 cm) | 0,005 (0,5 cm) |
The table shows the slope of the sewer pipe, which will ensure the normal operation of the system. If for some reason it is impossible to make the required angle of inclination (it happens in areas with difficult terrain), you can reduce the angle of inclination to the specified boundary norm. The chance of getting problems increases, but not by much.
What to do if the slope is more than required
Sometimes it is not possible to make the required slope – there are different conditions. In this case, there are two solutions:
- Lay the pipe as it turns out (but the difference per meter should not be more than 15 cm per meter) and hope that everything will work. With a large slope, it is recommended to install tees with upward bends on the track after a while – so that it is possible to clean blockages. The probability of their formation with large slopes of the sewer pipe is high.
- Lay the pipe with the recommended slope in the area where it is possible, then install the overflow well, again lead the pipe out of it at the desired slope. Several such wells may be needed.
A method of organizing sewerage in areas with a large slope – overflow wells
The first option is cheaper in the device, but it involves frequent blockages in the pipes. Of course, with heavy use of sewage (large amounts of water), there may not be any problems, everything can work without problems. But this is rather an exception. By the way, when using plastic pipes, the likelihood of blockages becomes lower – they have smooth walls, on which precipitation rarely forms. The second option is more expensive and time consuming, but it guarantees the system’s performance.
How to maintain the required slope
Determining the slope of the sewer is not enough. It still needs to be held while laying. The most convenient option is the presence of a special level with a goniometer. If there is no professional equipment, you will have to cheat.
There are ways to control the angle of the sewer pipe using the usual level:
- Having drawn a line on the wall with the desired slope, apply a building level to it, make a mark on the plastic in the place where the edge of the bubble is located. When placing the tubes, arrange them so that the bubble is in the desired position.
- If you take a meter level, you can attach a lining of the required width on one side. In short sections, this method does not work, but it is convenient to expose an extended pipeline.
Domestic sewage
When laying the pipeline, it is necessary to maintain a given slope, to prevent deflections and sagging. By the way, when laying outlet pipes from different plumbing fixtures, it is required to withstand different slopes (see photo below).
When laying an internal pipeline, you can draw the required slopes on the wall, and put pipes along them. You should not focus on the floor level, it is better to beat off the horizontal line. It is easier to do this if you have a level, if it is not, you can use a bubble level. After that, having calculated the required difference (described above), you “lift up” the far end. Once again check the accuracy of the calculations and the applied lines. After you can proceed with the installation.
In bathrooms and toilets, the required level is usually laid out with a thick sand-cement mortar. Anyway, then the pipe gets off – a drywall box is placed, on which the tiles are then glued. A more modern option – laying pipes in a strobe is not available to everyone – in panel houses there is no such wall thickness. When laying sewer pipes from the kitchen, stands and wedges are more often used. After the pipeline laid with the required slope is fixed to the walls with the help of special holders. They are installed in increments of no more than 40 cm.
Advice! When installing, turn the sewer sockets against the flow. So less likely to get leaking joints.
Outdoor sewage
Sewerage on the site is laid in trenches. When laying the track, try to make it as straight as possible. Any turns are a potential site for clogging. If you can’t do without turns, install a tee next to it, bring the pipe out just above the ground level and plug it with an airtight lid. This will be the right decision – you can quickly and without problems clean the traffic jams.
When laying an external sewer, they dig a trench with a flat bottom. The depth of the trench – 20 cm more than necessary – is a place for a sand cushion. With a small length and a small drop, the bottom can be left as it is – even. If the difference is large, you will have to form a slope. At this stage, there is no need to maintain the slope too much – do it approximately. Then the bottom is leveled, all stones and roots are removed, the pits are compared, compacted. There should be an even solid base.
Sand is poured onto the leveled bottom. It must be poured in layers of 5 cm, leveled, compacted (spill with plenty of water). Having laid 4 layers in layers, we get a pillow of 20 cm. Pipes are laid in the sand, forming a given slope. The slope can be checked with a long building level (1,5-2 meters or more). If this is not the case, you can attach a bubble level to a long even rail (beam) in the middle with adhesive tape. This way you can achieve the minimum error.
After the pipe is laid and its slope is checked, it is covered with sand. It should close it almost halfway. The sand is carefully leveled and spilled. After that, the pipe is 1/3 covered with dense sand (it is possible that the level is higher). Then you can fill it with soil.