Building new manhole,moving manholes and drains

Feminist issue with manhole name

In 1990, the city of Sacramento, California officially renamed all its manholes to “maintenance holes” out of concern for gender equality.The name “maintenance hole” was selected because the term shares the same initials as the word “manhole”, thereby eliminating the need to change the MH labels on the city’s utility maps.

Drains, sewers, waste and PC ( political correctness ) sometimes don’t mix. For some reason I find this amusing, just like saying stop valve instead of stopcock, some London Plumbers do that. We can call it inspection chambers.

From my experience, moving a manhole or building a new one, means that you are expanding the property by building a house or kitchen extension into the back garden or side garden. Not many people are happy with having a manhole in the middle of the brand new built extension. Or inside their house for that matter.

Another reason is a blocked up manhole. All the waste overflowing inside your property, all over the garden or under the floor – is not a pretty sight or smell.

blocked manhole
Blocked manhole inside a kitchen extension

However, many will find that a reasonable solution is to have a double seal manhole cover. Cheap and efficient, if you can afford the extra cost involved when moving the manhole outside the perimeter where the house extension will be. At least, any house extension builders or kitchen extension builder should make their client aware of the most popular way to save on underground building works.
manhole old cover
As you can see from the picture, all manhole covers look as bad as the ones in UK.
Going back to How to build a manhole, you must concentrate on two different and equally important things.
1. It means that you will alter or modify the existing sewer pipes.
2. You must build the new manhole in such way that it works better than the old one. At least that where you should aim at, because the original manhole was or is in the best place for a manhole to be, due to the original layout of the waste pipes.

Building the new manhole

Dig the new place for the new manhole well below the lowest point for the drains – about 35 cmm to 50 cm, depending on the soil. The smallest internal size of a manhole is 0.6 m by 90 cm or in millimeters = 600 by 900 mm. This is the INTERNAL size, so you must calculate the external size too. A good bricklayer can start with a bigger base and end up with a smaller opening, just like a bottle neck shape, yet rectangular built manhole.

Get o good solid base, using water proof concrete and DMP, because you will build the manhole in a similar way to a swimming pool. If the manhole leaks, in the summer, your garden can smell like a toilet because the waste water will penetrate the walls – into the garden soil.You might not see it, but it will be there. And when is hot, the water evaporates, thus the smell will be very present. Doing a good job will avoid many unpleasant things like smell and an unhygienic sewer system.

base for new manhole
The concrete slab will form the base for the manhole and act as a foundation at the same time. Using Engineering Bricks together with a Water Proof Liquid in the cement mix, start building the walls. Make sure that there is no gaps unfilled, where the water can find its way out. If you are building the manhole’s walls ( sorry, I mean the inspection chamber’s walls ) in a stretcher bond and line the walls with DPM, you can proceed like in the picture below.Traditionally, most inspection chambers were build using solid walls.
manhole walls
You might notice the pipes or soil pipe already in situ, that is because it helps the bricklayer building around them. You should end up with this :
new manhole
You might notice in the picture that the manhole itself is bigger than the opening , the bigger the manhole, the better, even if it means 0.4 cubic meters. At Robuild we normally use double seal covers even when the manhole is positioned outside. For double measure, render the walls inside the manhole, using a water proofing cement mix in two coats. Render the walls in such way that nothing sticks to the walls, everything must go into the drain at the bottom of the inspection chamber and into the drain. Like a bottle neck upside down.
manhole garden

I am going to draw a crude diagram myself because the architect is not available right now. For the pipe work, make sure that everything is romantic. No obtuse angle is allowed. An Obtuse Angle is more than 90° but less than 180° . The key word is ; if it flows , the inspection chamber works. Avoid using 90° pipe meeting the inspection chamber, it will just splash onto the walls and that is not a romantic manhole or a good job. The metaphor means = use a soft angle, let the water and waste flow naturally, gravity works if you don’t stop it working.

rude manhole

Moving the manhole

In legal terms is called : a diversion. If its a conservation area, you will have to use clay pipe and use the right slope for the drains to work. Make sure you tell the neighbours in advance about it, dealing with live sewer pipes is not a good idea. Work should take place after the new pipes are laid and you just have to connect the new pipes, a job that should be best done during the night with the right illumination equipment and the right people on site. Between 2 o’clock and 4 o’clock, is the best time, because people are sleeping and not taking showers or using the toilets.
clay pipes


Does a new manhole need a planning permission in a conservation area? The accepted planning permission said old drains will be used.

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