Invert Level

Published: December 6, 2018 | Last updated: July 5, 2023

What Does Invert Level Mean?

An invert level is defined as the elevation of the inside-bottom of a pipe, trench, culvert, or tunnel. It may also be considered the "floor level" of a pipe.

Invert levels are essential for assessing the flow in a piping system. For example, the invert of a municipal sewer connection can impact the sewer system of a newly constructed house or building.

Invert levels are determined by measuring the vertical distance from a fixed datum to the lowest level of a pipe. This is typically done using a pipe laser or some other type of surveying equipment. Engineers will then use this data to come up with drainage plans or alternative drainage systems.

Pipe inverts are especially crucial in systems that rely on gravity flow, i.e., non-pressurized pipe fluids. As such, the invert level of the pipe’s outfall must be lower than the level at the upstream end.

This parameter can also be used to determine pipe grades or slopes. For example, if you know the incoming and outgoing inverts between manholes, the sewer pipeline grade can be determined using simple trigonometry.


Trenchlesspedia Explains Invert Level

The invert level is so-called due to its resemblance to an upside-down arch. An inverted arch has its rounded tip (crown) pointing downward. Its counterpart, obvert level, is the elevation of the highest interior point.

Just as the invert is referred to as the ‘floor’ level, the obvert is considered the ‘ceiling’ level. These terms are commonly seen in architectural and construction drawings.

How do Invert Levels Influence Piping Design?

As mentioned before, invert levels are particularly useful when designing piping systems that rely on gravity flow. When assessing these types of drainage systems, engineers and contractors need to ensure that the piping flow remains positive. In other words, the fluids must be allowed to flow from a high point to a low point on a consistent grade. Therefore, for this type of flow to be achieved, the invert level at the outlet must be lower than the invert level at the inlet.

Invert levels do not only apply to sewer piping systems. All infrastructure responsible for transporting fluids without the aid of external pressure relies on the inverts of their inlets and outlets. In buildings, invert levels must be coordinated to ensure that drainage systems function efficiently.

For example, when designing the layout of a floor drain piping system, inverts must be located below floor level. Also, for drainage systems that are required to discharge into existing water bodies, the invert level of the pipe outlet needs to be placed at the appropriate elevation.

Invert levels are an essential component of construction drawings for all sanitary and stormwater systems. This information ensures that contractors locate and install pipes at their intended elevations. Mechanical engineers may also coordinate with civil engineers for specific types of internal piping/drainage systems, such as those required for HVAC and specialized equipment.

Placing pipes at incorrect invert levels can result in poor drainage, clogs, backups, and flooding.


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