What should be the slope of the sewer pipe according to construction standards

Nikolay Fedorenko
Checked by a specialist: Nikolay Fedorenko
Author: Tatyana Zakharova
Last update: April 2019

Preliminary calculations for a sewage system protect against potential technological problems, for example, from clogging. Correctly selected pipe diameters and competent installation ensure a long and comfortable use of the waste system.

One of the important indicators in the design and installation of communications is the slope of the sewer pipe, necessary for the free movement of drains.

We will tell you how to calculate a sufficient angle of inclination of the pipeline, what rules should be followed when wiring the internal and external sewer systems.

What is the slope angle of sewer pipes

One of the principles of pipe installation, which is used in practice by experienced builders, is the ability to install the mains in such a way that the wastewater moves by gravity. This principle is applied everywhere - both in the arrangement of apartments in high-rise buildings, and in the construction of private 1- or 2-story cottages.

Horizontal branches, for which the slope angle is calculated, is installed after the risers are laid and fixed - vertical sections of the sewer. Risers are distinguished by a larger diameter than other pipes.

Horizontal branches are connected to the risers using fittings (tees) and sent to the side of plumbing fixtures (toilets, sinks, bathtubs, showers) along the smallest path.

The angle of the pipe from the toilet
Most often, toilets are mounted near the riser - plumbing fixtures that "give" the greatest amount of solid waste. The shorter the path for solid waste to exit, the less likely it is

And now we will analyze the definition of the slope angle of a horizontal sewer pipe - external or internal.

Imagine that a straight line runs along the laid highway parallel to the floor or the surface of the earth in the case of external pipes. If the beginning of the line is connected to the lower end of the pipeline, then we get the angle - with proper installation. This is the slope angle.

It is measured in degrees or, which is easier to understand, in centimeters per linear meter - cm / linear m.

During the construction process, for convenience and ease of calculation, just pull the cord aligned horizontally. Its beginning is fixed at the lower point of the highway, and the end is brought under the upper. Angle measurements are relative to him.

The calculation of the slope angle is directly related to pipe parameters such as length and diameter.

According to the standards set forth in SNiP, the diameter of the horizontal branches of the internal wiring must meet the following standards:

  • D 40-50 mm - from dishwasher or washing equipment;
  • D 50 mm - from sinks, sinks, bathtubs, urinals (i.e. appliances with liquid drains;
  • D 110 mm - from toilets.

For external sewage, a pipe diameter of 110-160 mm is provided.

Sewer slope
There are options when you have to combine pipes of different diameters. For example, a toilet pipe is attached to the drain from the sink (50 mm). Obviously a 110 mm pipe adapter is required (+)

It is important to choose the right diameter and slope of the communications, otherwise the system will often fail. Consider the possible negative consequences.

How system functionality depends on slope

During the installation of the sewer system, pipes are laid either directly (parallel to the floor) or at a certain angle. The first option is clearly erroneous, since it blocks the movement of effluents and, ultimately, makes the entire system inoperative.

Incorrect slope of sewer pipes
Judging by the photo, the pipes are not even laid parallel to the floor, but with a slight slope towards the bathtub - that is, incorrectly. When you turn on the water in the sink, it will not flow towards the riser, but directly into the bath

The second solution is correct, but it can be implemented in different ways:

  1. Provide the sharpest angle.
  2. Make the slope minimal.
  3. Perform installation, focusing on the numbers recommended by regulatory documents.

What will happen in each of these cases?

Option 1. It would seem that the angle is too sharp, therefore, the steep descent of the drains is not dangerous. This opinion is erroneous, since the rapid flow of a liquid does not fully ensure the washing off of solid waste.

As a result, they accumulate and form blockages. The second trouble is related to the breakdown water locks, the result is a specific smell of sewage in the whole house or apartment.

Noisy pipes with a large angle of slope
Another undesirable and disturbing consequence is the loud noise that wastewater falling down at a high speed creates

Option 2 The minimum slope is not much different from horizontal installation. Slow fluid movement entails siltation, the formation of a thick layer of dirt on the walls of the pipes, and then regular blockages. By the way, SNiP recommends adhering to the speed of runoff within 0.7-1.0 m / s.

Option 3. The most optimal solution is to ensure the slope indicated in the regulatory documentation, which shows the dependence of the laying angle of the trunk on the diameter or length of the pipe. We proceed directly to the norms and calculations.

What standards should be observed?

Let us dwell on construction standards, which are detailed in SNiP. About the features of the internal sewage can be read in SNiP 2.04.01-85, external - SNiP 2.04.03-84. It is also useful to refer to the regulatory documentation GOST 25150-82.

Features of the house sewage system

There are two options. arrangement of internal sewerage - hidden and open installation. The first is to mask the wiring behind the wall panels, under the flooring and in the ceilings, the second is to lay in open areas.

Masking sewer pipes with a slope
One of the options for flush mounting is full or partial deepening into the walls. In brick and panel houses for this type of disguise, gating is practiced, followed by finishing - plaster, drywall, ceramic cladding

The type of installation, in particular, determines the permissible length of the pipeline:

  • hidden lines must be no longer than 10 m;
  • open pipes they can be longer, but provided that they are installed at a defined slope and with free access for maintenance purposes.

The diameter of the pipes must necessarily coincide with the diameter of the releases of plumbing fixtures. To connect the mains to the risers, shaped elements are used - crosses and tees of the direct type for connection at an angle of 90 ° and oblique type for fixing at angles of 45-60 °.

Distance between revisions
Despite the correct, with a slope, the location of the hidden pipes for the purpose of maintenance, inspection cameras are arranged - both on bends and on long straight sections of the highway (+)

Requirements are presented for turns: they must be smooth, from 90 ° or more, that is, not sharp. For a safer change of direction of the pipe create a design of two turns of 135 °. When connecting parts, the sockets should be turned against the flow of wastewater. The only exception is the installation of double socket couplings.

In SNiP the permissible values ​​of the slope of the sewer pipes are indicated. The data are shown in the following table:

Slopes of household sewage
Standard values ​​are given depending on the diameter of the pipes, in units that are read as the number of centimeters per linear meter. For example, when installing bends with a diameter of 50 mm, it is necessary to withstand a slope from 0.025 m to 0.035 m (from 2.5 cm to 3.5 cm per meter) (+)

It turns out that with a sewer line length of 5 m, the difference in height above the floor between the beginning and end of the pipe will be 12.5 (17.5) cm = 2.5 (3.5) x 5.

Let's go back to the “help” of the construction cord - it just might come in handy. If it is stretched along the entire length of the pipe, but parallel to the floor, it just turns out that the distance from the cord to the lower end of the trunk is 0 mm, and to the upper - 12.5 (17.5) cm.

As is clear from the table, with an increase in the diameter of the pipe, the slope value decreases, that is, for D 110 mm, the optimal inclination angle is 2 cm / linear m.

The table shows the minimum values ​​of norms. There is also a maximum slope - it is 0.15 m / running m. The value is relevant for pipes of various types and sizes, except for the shortest branches, the length of which is less than one and a half meters.

It can be concluded that the angle of inclination for sewer pipes should be between the data from the table and 15 cm / linear m.

Sample Internal Wiring Project

The project should begin with the drawing up of diagrams, drawings and sketches with simultaneous calculations relating to all branches.

Particular attention should be paid to the following points:

  • the location of pipes, fittings, joints;
  • diameter of pipes and fittings;
  • the length of each section to the riser;
  • the height of the flooring or the mark of floors, niches, etc.

In addition to the exact measurement values, the tolerances should be taken into account: for each branch of the trunk ± 20 cm, for the length of the riser and branch ± 1.5 cm.

Metering card
Sample metering card for installing sewer pipes for two apartments connected to a common riser. Two parts are absolutely identical and are located in mirror image (+)

For this scheme of a sewer comb, measurements of the distances between individual points, namely the central axes, are important:

  • riser and sink;
  • bathtubs and washbasins;
  • toilet bowl and washbasin.

It is also necessary to take into account the thickness of the wall that separates the plumbing blocks of two adjacent apartments.

Read more about designing the internal sewer wiring of a private house in this article.

Outer pipe laying

Unlike internal sewage pipes, which can be both open and masked in ceilings, external highways are classified as hidden communications - the pipeline is placed in the ground.

Pipelines most often have access at the level of the foundation of the house and lead to treatment or storage facilities. Throughout, they should have a diameter of at least 110 mm and a clearly defined slope of 0.02 m per linear meter.

In addition to the mandatory bias to the external highways, a number of requirements are also imposed.For example, they must also be equipped throughout. manholes.

If the highway is straight, then a well is arranged every 10 m, if it has bends, then in places of turns. Technical wells are also required where several highways intersect or there is a step transition.

The maximum number of inspection wells is necessary to anticipate the occurrence of blockages in the most predisposed places: at bends, at junctions, etc. (+)

For outdoor sewage use different types of pipes, their cross-section is from 110-200 m. As we already explained above, the slope angle depends on the internal diameter of the pipeline, therefore we take this into account when arranging trenches and laying communications.

Do not forget that for pipes of large diameter smaller values ​​apply:

  • at D 150 mm - from 0.007 m to 0.01 m;
  • at D 200 mm - from 0005 m to 0.008 m.

These are the minimum values. When installing a short fragment of a pipe with a large cross-section, a miniscule slope may not be noticeable, but for long pipelines the differences are obvious.

For example, when laying a pipe with a diameter of 15 cm, it was decided to make a slope of 1 cm / linear m. It turns out that for every 10 m the difference is 10 cm, and after 100 m it is 1 m. This must be taken into account and combined with the parameters of the groundwater level, as well as with indicators of the level of freezing of the soil.

How to control the slope

For an example of installing an external highway, take the laying of a single straight pipe leading from the building to the septic tank.

The purpose of the pipe is to move the sewage coming from plumbing fixtures to a common tank. This is greasy waste from the kitchen sink, and fecal matter from the toilet, and dirty water from the shower.

It is reasonable that the pipe should be at least 110 mm in cross section. It is important for us that the necessary slope is maintained throughout the pipe, in this case - 0.02 m / linear m.

Using the laser level, you can measure the slope at different stages of operation. A photo gallery will help visually present controlled work sites.

If the angle of inclination is maintained in all places, there will be no problems with the movement of sewage water. However, it should be remembered that in the future, the result of undetected errors can be the complete dismantling of the external highway, therefore, each measurement must be taken very seriously and not do it “by eye”.

Calculation of the level of fullness of the highway

Additional calculations of the level of filling, along with the angle of inclination determined according to SNiP standards, provide trouble-free movement of sewage drains through the pipeline.

Calculations are made according to the formula:

Y = H / dwhere

  • Y - level of fullness;
  • H - fluid level in the pipe;
  • d - diameter

A value of 1.0 means that the line is completely filled with drains - this can only happen if the layout of the wiring elements is absolutely horizontal.

Tube fullness
In SNiP the norms of minimum and maximum permissible filling are indicated - 0.3 and 1.0, respectively. That is, if the pipe diameter is selected correctly, the waste will move at the desired speed without sticking to the inner walls (+)

In this regard, it is customary to take values ​​in the range of 50-60%. In practical applications, occupancy is taken into account, which is greater than 0.3 and less than 0.6. The optimal value is considered to be 0.5-0.6.

Let's try to calculate the flow rate on our own.According to regulations, it should be 0.7 m / s or more. Only at such values ​​does the fluid freely reach the final goal.

Suppose that H is 60 mm and D is 110 mm, the pipes are made of plastic, that is, they have a smooth inner surface and a minimum degree of resistance. According to the formula 60 we divide by 110, we get 0.55 - this is the level of fullness (Y), it corresponds to the norm.

Conclusions and useful video on the topic

Information from the videos will help you understand the complex nuances of installing a sewer pipeline.

An example of correctly mounted pipes in a bathroom:

Detailed explanation of the theoretical part:

Useful device for observing a slope angle:

Compliance with the norms when calculating the angle of inclination of sewage pipes is of great importance in terms of technology. Calculations are best done at the design stage of the internal wiring or external pipeline device.

If you have any difficulties, we recommend that you contact a professional design engineer.

Is there anything to supplement, or have questions about determining the slope and wiring of sewer pipes? You can leave comments on the publication. The contact form is located in the lower block.

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Visitors Comments
  1. Andrew

    Sewer laid sewer when he was thirty years old. He could not boast of knowledge in this area. Now there are problems that are still being solved, but I'm already tired of this.

    The fact is that from the exit from the house to the entrance to the pit, there are as many as four bends on which the growths formed. It is difficult to deal with blockages with a cable. There is little space in the yard, there is nowhere to dig a new pit. Dig up the existing one - lose convenience for a week. So I don’t know what to do. Did someone solve such problems?

    • Nikolay

      Good afternoon! It came up with the idea to use a 110 mm pipe for water supply, black with a blue stripe - can it be laid in one piece and give the necessary radius where necessary?

    • Expert
      Nikolay Fedorenko

      Good day, Andrey. The only right solution is to unearth the existing one and make a complete replacement.

      In addition to the problems that have arisen, another one is shining soon. The service life of the joints is much shorter than that of the pipes themselves. Given the lack of knowledge of the father-in-law, I assume they have already begun to leak.

      This will lead to leaching of the soil under the pipes, and since cast iron is brittle, the pipe will break, unable to withstand the pressure from above. In this case, you have to do the same work, only knee-deep in feces. I recommend not to delay the solution of the issue.

    • Dmitry

      Put a new branch, but forget about the old one! If turns cannot be avoided, it is necessary to put manholes!

  2. Michael

    Of course, you can lay sewer pipes directly parallel to the floor, but then there will be problems with blockages. I disguised the wiring behind the wall panels after making a bias. It turned out well and the view is pleasant. It turns out the sewer pipe, also under a slight slope from under the foundation, and is led into a trench all the way to the sewer pit. The angle of inclination was made by level. Five years have passed, so far no problem.

  3. Sergey Nikolaevich

    I have a private house. During its construction, such a question also arose.I made a sewer with a slope, so that the water by gravity quickly left. The angle was slightly larger than shown in the video, but then there were no problems, and to this day there is no. As for laying pipes in an open area, I immediately abandoned this venture, since there is a risk of freezing in winter. This option is the worst. I dug a pipe deeper than the freezing level in our region so that it would not freeze. The material is the same as in the video. Everything is correctly described for you, the technology proposed is correct. For those who have a private house or are building, this video is useful. Take note boldly.