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

Drains, manholes and sewers

For whatever reason you might need to build, modify or adapt the existing waste system, it is a good idea to understand how it works before you start working or laying new pipes. Drains, manholes and sewers are usually jobs undertaken by ground workers with experience because everything is underground. Get it wrong and it will be expensive to repair any mistakes made. A very interesting video was released by Thames Water in order to raise awareness among Londoners.
Thousands of people suffer the misery of blocked water drains and sewers each year caused by unsuitable products, including wet wipes and sanitary items, going down the drain.
Keep in mind that the sewers in London were originally built in Victorian times and not designed to cope with the population that is today.
london sewers
If you live in London, your house should be detached, semi – detached or terraced. And that means, you are sharing the same sewage with everyone in London. In a dubious but amusing way, every single WC or drain, is connected in the true sense of the word. More or less, this is how it works.
In London, these days, there is an attempt to separate the clean water from the dirty water by using surface drains or rain water drains where possible.
The manhole acts as a chamber along the drain pipe and it happens very often that properties or houses situated at the end or beginning of the terrace line of houses are the ones with most blockage problems or backup drains and manholes.
terrace houses
In fact, the problem lies with the position of the manhole, if the property is first on the row and the main waste pipe gets blocked, there will be not enough pressure building up inside the pipes to push the blockage naturally. If the property is at the end of the terrace row, and the sewer gets blocked, the manhole will be the first to overflow.
clean manhole
The main reason for that is gravity, all the liquid waste works based on gravity and you can easily imagine that the bottom or the the lowest point inside a pipe that is not leveled, will fill up first. So, in case you have arguments with the neighbours regarding who will pay for the emergency plumber or drain cleaners, keep in mind that problem can be a very shared terrace row blockage. Then again, most drains are very old, Victorian clay pipes and it happens very often that parts of the pipes would simply collapse, and this is a very common cause for blockages in London.
colappsed pipe drain
Of course, Thames Water or Thames Valley will ask its customers to focus more on what you pour down the drain. In the bathroom or in the kitchen.

There are over 20 companies supplying water in England and Wales.
Scotland has only one water authority.
Northern Ireland has only one water authority and domestic customers do not have to pay water rates.
There are water only companies and combined water and sewerage companies.
You can pay a standing charge for water or have a meter.
Water rates differ across the UK.

You cannot switch your water supplier.

Bricklaying, building walls

Building new walls for a house extension wall or a garden fence for that matter, deploys the same technique. You can have a cavity wall or a solid wall, depends on your requirements. In UK, bricks and blocks are the most common materials used to build walls. Stones, sometimes are used for special properties and walls.

The most elegant type of brick walls, and efficient too, is the stretcher bond type.

brickwall types

Old bricks or re-used bricks, can give the new building a more ”stable” look, because most new buildings can stand out like a sore thumb.
reused bricks
You could also use a variety of combinations between blockwork and brickwork.
The picture above shows a 2 storey side house extension, blockwork at the rear and brickwork on the side.
As you can see in the picture below, there is a perfect balance between the two.
brickwork wall house extension
If you want a more modern look, you could also use glass block, built into the brickwork or blockwork.
glass blocks

Remember to start building the walls on a good foundation, under the DPC is recommended to use concrete blocks, finished off with one or two layers of engineer bricks. The reason for that is the wall below the DPC is exposed to the elements and damp. Between the foundation walls, you should use a lean concrete mix, but don’t top it up, leave a gap of 10 cm for the water that might collect between the walls. Wall ties also must be used to ensure a good and strong structure.
walls below DPC

The DPC – Damp Proof Course, is very important. It has to be above the ground level at least 15 cm and that includes any slabs or finishing materials. For the external wall, you can use the 100 mm wide DPC, and for the interior wall, you must use the 600 mm wide DPC. The overlapping DPC it will go under the DPM Damp Proof Membrane and seal the internal wall from any raising damp if the internal floor is faulty.
DPC and DPM walls
The wall ties must be kept free of cement, mortar, muck mix. The insulation and the muck can act as bridge between the external wall and the internal wall, thous if the external skin wall is exposed to heavy rain and gets wet, the water can travel to the internal skin wall.
Wall ties are used at a density of 2.5 per sq. metre, tie centres measuring 900mm horizontally and 450mm vertically, in a domino pattern or Z – N shape. At the corners, keep a bit of a gap.
Weep holes or “weeper holes” are small openings left in the outer wall of masonry construction as an outlet for water inside a building to move outside the wall. You must used them, together with DPC where a metal lintel above the openings can gather the water. You can use Plastic “weeps” or just leave a gap between the bricks.
weeper holes and DPC lintel
Another important aspect is the cement mix for bricklaying. Never mix more than you can use, before the cement in the mix starts to set, otherwise the solidity of the wall will be compromised. Also, using to much cement in the mix can create cracks in the walls by being to rigid, because a building or any structure needs a bit of flexibility while the structure sets down, a process that can take years.
A good bricklayer can lay from 600 bricks upwards, but if you are an amateur bricklayer, 100 to 300 bricks including setting out the corners, is reasonable.

Stone walls are arguably the most ancient way of building walls. There are two types, dry walls and wet walls. In UK both types are popular, the dry walls can be used for fences and wet walls are used in combination with the cement mix.
stone walls

Foundations or footings for walls and new building structures or dwellings

Foundations or footings for walls and new building structures or dwellings guide.

Getting a foundation or footings right is paramount for the structure of the new building. If you build a shed, an easy way to do it, is to employ the pillars or pier foundation technique. You must keep in mind that the technique is not design or recommended for very heavy shed structures. If you use light weight materials, light blocks instead of the solid brick walls, flat roof instead of tiles roof, it will do just fine. In combination with concrete lintels, you will save a lot of digging work, soil to dispose , skips and concrete.
pillar foundation sheds
You might notice in the picture above some square looking holes, that is where the concrete goes. It should be deep enough to be stable, depends on the quality of the soil and the weight of the structure. If you want to go hi tech and engineer style :
Foundation design is a complex process. It depends on the total load on a particular foundation as well as the Safe Bearing Capacity of the soil.

For example, a single storey building foundation with hard soil, where total load on footing does not exceed 300kN, a footing pit of 1M X 1M at a suitable depth up to hard strata would be sufficient. The pit would have a 6″ layer of PCC. On top of that, you would place a mesh of steel consisting of 8 rods each of 10mm diameter on both sides. Then place the column steel frame on top of it and tie the column bars to the steel mesh. Pour 6″ of concrete and let it harden. Then you can go for either tapered footing or block footing. Total thickness of block should be 15″, including the 6″ you of RCC poured earlier. So, for a single storey building whose load does not exceed 300 kN, and the soil strata is hard, the above given design should be sufficient.

Four loads are to be considered in order to measure total load on the footing:

Self load of the column x Number of floors
Self load of beams x Number of floors
Load of walls coming onto the column
Total Load on slab (Dead load + Live load)

If you get well versed with load calculations, then calculating the size of the footing and following the procedure for foundation design wouldn’t be a problem.

To keep everything simple, the holes – pillar foundation should be at least 600mm deep and width depends on the size of the wall, if you have a cavity wall, make sure the footings are wide enough to accommodate the walls easily , as the wider it is, the better at spreading the dead weight. ( in London you don’t get much snow and if its a flat roof, the wind won’t affect the live weight as much )
Then you use pre-stressed concrete lintels to bridge them, and in this way, the savings in labour and material becomes obvious.
pier foundation
I don’t have a real picture but its fairly simple to understand the process.
building shed walls

The most common type of foundation is the traditional type, basically you dig a trench and fill it with concrete. If you build a house or a house extension, the Building Control will ask you to do it this way, unless you can afford a good structural engineer and some expensive drilling equipment if the soil – ground is really bad. Remember that Venice is built on wooden piers.
trench foundation
In order to keep the Building Inspector happy, remember to keep the foundation clean, all the muck from the bottom of the trench must be cleared before pouring the concrete in.
water filled trench foundation
If the water table is high, it is very probable that the trench will fill up with water overnight, or if its raining. You can use a bucket if there is not a high volume of water or you could rent a water pipe pump.
water trench footings
The concrete can be mixed on site, you could buy a concrete mixers and all the sand, gravel and cement and do the mixing yourself. If its a D.I.Y project and the foundation is not more than 3 to 4 square meters, it will be a good physical exercise as once you start mixing the concrete, you will have to complete the foundation before the concrete sets.
concrete foundation
I would rather recommend C25 concrete for larger foundations, on a 1:5 ratio of cement to ballast. The strength of a concrete mix is measured in grades. There are different concrete grades for example C15, C20, C25.
And if the foundation is really large and it can not be completed in one go, it will have to done on segments, using metal reinforcement rods/bars between the segments of the footing in order to connect them.
foundation C25 concrete

Building a house extension in London

In London, most home owners decide to extend the property to get extra space. The design and layout of the new house extension is quite limited, due to practical and planning permission rules.

A kitchen extension can also give you the opportunity to remodel the ground floor, for example if you want an open space ground floor and kitchen extension. Of course, removing solid external walls, made of bricks and supporting the whole house structure and the roof, is not a DIY job.   To start with, a Structural Engineer is needed to check the wall loads and the type of metal beams needed, then everything will be written down and the Structural Calculation submitted to the Building Control for inspection and approval. For simple opening into the wall, or to enlarge lets say, the kitchen door, RSJ beams will have to be laid on padstones.
Metal Beams Structure Support
The dinning room can be separated by using partition walls.

A house extension can be built in different shapes and sizes. A popular choice is the so called L – shaped house extension, which can be a 2 storey side extension and 1 storey kitchen or rear extension. The picture below shows the front of the house, the extension was built in such way that looks as part of the house and is not obvious that the original property has been extended.

L shaped house extension
As you can see in the picture below, the rear extension is a single house extension and with a flat roof.

rear house extension

In order to have an open space ground floor, extensive metal works – RSJ beams, was used by the builders.
RSJ beams

House Extension Builders

Building a kitchen extension

Do you know how a kitchen extension is built ? We’ll try to write a How to build a kitchen extension guide that can help you understand better the construction process. Kitchen extension company in London. If the kitchen extension is at the rear of the property, and it will be extended into the garden, the normal size for the kitchen extension is about 5 meters by 3 meters and the new dwelling is built where normally the garden patio is.

Foundation or Footings
There are two ways that the kitchen extension builders can dig the foundation. If the property is a terraced house and there is no access to the garden through an alleyway, the trench for the foundation will have to be manually dug, the way it is illustrated in the picture bellow.

Fondation for a rear kitchen extension

If there is access to the garden, mechanical digger can be used, making the job faster and cheaper.
Mechanical digger digging foundation

The soil from the foundation will be taken by wheelbarrows, through the main house and to a skip that usually is located onto the drive way or onto the street if necessary. A street skip licence will be needed if the skip is kept on the main road and it will have to be illuminated during the night for safety reasons. You should expect some damages to the walls and floor, as there will be heavy traffic caused by workers and materials.
Skip on the driveway

The foundation should be about 1.2 meters deep and 600 mm or 0.6 meters wide, depending on the quality of the soil. Solid clay soil is the best type for foundation, sandy type will require deeper footings. The Building Control Inspector from the local council will advise how deep it should be, before the concrete is poured in.
Trench footings
Again, if the house is a terraced property and there is no access for the concrete lorry to pour the concrete directly into the foundation, a concrete pump can be used.
Concrete pump and lorry
The concrete is pushed through a 4-5 inch pipe.
concrete pipe
If the concrete lorry has direct access to the foundation, it will make the jobs easier, faster, and cheaper.
Concrete poured directly in the foundation

After the concrete is pored in the foundation, it will takes few days for the concrete to set before the walls for the foundation can be built. New plumbing waste or soil pipes will be needed in most cases, but we will write about how to run new pipes or construct a new manhole in a future blog post.
Footings with concrete

Building the walls for a kitchen extension
If the new kitchen extension is built using cavity walls ( most of them will be constructed with cavity walls for better heath conservation ) the walls under the DPC (damp proof course) can be built using concrete blocks, topped with engineered bricks to stop the damp rising to the main walls.

The walls for the kitchen extension can be double skin block-work or the external skin brick-work and the internal skin block work. Using blocks for the walls,inside and outside, will help the bricklayer finish the job faster,but there are some drawbacks as the external and sometimes inside walls too, will have to be rendered with a smooth finish or pebble dashing, to match the exterior of the property. Building Blocks are also cheaper than bricks.

Blockwork double skin cavity wall
Cavity walls with external brick faced skin, has the advantage of being easier to maintain long term and it looks better, especially in London, where traditionally the bricks are the favourite choice of building houses.

Brick faced cavity walls

The gap in between the walls can be be from 35 mm to 900 mm, however, the most popular choice is 75mm. The bricklayer will have to keep the walls clean and free of mortar, as the mortar for the masonry, can act as a bridge between the walls, and damp can travel from the external wall, to the internal wall. Insulation is then inserted as building process takes place.

Building the opening for doors and windows is done by using wooden frames and build the walls around it. Experienced bricklayers can do without frames, however it is recommended to use them to make sure all the openings are perfectly square, thus avoiding any nasty surprises when fitting and installing the doors and windows.
Kitchen extension interior
Concrete lintels can be used for walls that will be rendered or cavity wall metal lintels.
Metal cavity lintels

Building the Roof for the kitchen extension
There are two main choices for the roofing. Flat roof and Pitched roof. We will start with the flat roof, as it is cheaper to build and a popular choice. The carpenter will have to lay wall plates on top of the internal wall and attach the wallplates to the walls using brackets. The wallplates are timbers , 47mm x 100mm or 4” by 2” as is known among the carpenters.
basic flat roof construction
Flat roofs can be so called Cold Flat Roof or Warm Flat Roof, depends where the insulation is located and the gap between the ceiling and top surface of the roof itself.
structure of the flat roof
The timber used for the main structure of the flat roof should be water treated to last longer.
timber roofing
Finally, the external grade plywood can be laid after the slope of the roof is set by using runners ( the flat roof just looks flat but actually has a slope to allow the rain water to run off into the guttering ) and then the bitumen layers can be cross laid.
bitumen layers for flat roof

A pitched kitchen extension roof looks better and it will last longer.
pitched kitchen extension roof

Using old roof tiles helps matching the new extension roof to the old property.
kitchen extension