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Assuming these give access to foul water drains which can get blocked, problems would arise in trying to clear the blockage. Access covers, in my experience, are embodied in any new surface; some are framed to accept patio and driveway materials.

Glenda – It could be a problem when you come to sell the house if the buyer has a comprehensive survey and tries to trace the route of all the soil and waste outlets to check that they are clear and free-running.

In most house purchases these days it is standard practice for the buyer’s conveyancer to obtain a detailed utilities plan of the property showing the routing of all mains services including surface water drainage and foul water sewerage and marking the position of inspection chambers or other access points that were required under the building regulations at the time of construction or for later works, so it will be clear to the buyer that there are buried inspection chambers under the drive and under the patio. This would become apparent before exchange of contracts so the buyer could withdraw from the purchase or use the information to renegotiate it.

The inspection chambers usually give access to places where a number of drainage branches join before the outfall to the main sewer, where new connections have been made after the house was originally built, or where [in a combined drainage scheme] one sewer connects a number of properties so that each section can be rodded-out or pumped-out if necessary without flooding other sections further along.

While it would be recommended that you do expose and reinstate the access points with new covers, nowadays it is possible [but not necessarily cheap] to undertake CCTV surveys of the drains from the nearest point where a camera can be inserted. This would avoid having to excavate the inspection chamber in order to see if there is any blockages or tree root penetration. It is also possible to evacuate the drain with a powerful suction hose and tanker or with a motorised corkscrew-like device that can break down a blockage, but that also depends on the proximity of an access point which could be in the public highway or in someone else’s property and incur a cost for approval and/or the employment of a specified contractor.

The access point under the drive is most likely to be the most important one since it is probably the foul water drain connecting into the public sewer. The one under the patio is more likely [but not necessarily] to be for surface water drainage joining together the outfalls from the roofline downpipes to enable them to discharge into a soakaway in the garden; these tend to suffer less from blockages as they are frequently flushed by heavy volumes of rainwater from the roof; however, moss, leaves or other debris in the gutters can build up and prevent the outflow. The inspection chamber is often the best place from which to remove such material so has an important function.

To avoid problems during your occupation it is important to check on the condition of drains to make sure they are flowing freely. It is best to take care over what goes down the toilets and sinks; non-paper wipes, grease and food residues are particular items to keep out of the system but powders and thick liquids can also coagulate. If any problems do arise caustic soda can be used in solution to clear the outlet but it is hazardous stuff and the instructions must be followed strictly.

Inspection covers allow you to find how far a blockage extends. The usual blockage, in my experience, is caused by inappropriate materials being flushed into the system. My set of drain rods pushed down the nearest inspection chamber to the blockage deals with those. Not a pleasant job. I have not used a home pressure washer hose but presume that would need to be pushed through the pipes close to the blockage to have any effect? Like drain rods that would best be done from the nearest manhole. So I think losing local access to the pipes by covering inspection covers is a mistake.

Good advice, Em. It certainly pays to take care of your drains.

It should not be assumed that modern properties are immune from drainage problems because the drains are formed in long lengths of plastic pipework. In a previous house built in 1984 the drains ran along from the back of our house past four more before reaching the public sewer picking up connections from the intermediate houses along the way. Occasionally sewage would back up and start to emerge from around the inspection covers preventing our wastes from emptying. I had a set of rods that could extend for about sixty metres so I would be able to clear the blockage by pushing and turning the rods to dislodge the obstruction — I could tell which house was responsible by checking the number of rods used before resistance was encountered; it seemed to happen after a neighbour’s family with their babies came to stay.

An earlier house built in 1902 had excellent 6″ diameter drains and never caused a problem until a very dry summer in the late 1990’s caused the heavy London clay subsoil to dry out causing disturbance of the drains; tree roots seeking moisture started to penetrate the joints between the drain pipes leading to failure and also to subsidence of the rear of the property. Luckily most of the cost of the remedial work was covered by the building insurers and one of the very good things that they carried out was to line the original pipes out to the public highway with a continuous fabric membrane so that any future rupture would not necessarily allow sewage to leak out or tree roots to creep in.

Although older houses often have much shallower foundations than modern properties they were often constructed to very good standards and have stood the test of time, even Victorian terraced properties built on steep hillsides have survived well in many areas. Bombing in the 1940’s did most damage but the repair work was usually done to a high standard.

I always got a sense of satisfaction from rodding the drains. Putting on the protective clothing, getting the rods out and fitting* them together, flushing everything with copious amounts of water, and sanitising everything with Jeyes Fluid and its potent aroma! What’s not to like?

* I had to substitute this word for “screwing” because of the intervention of the profanity filter. Comment now orthodoxly sanitised.

Much like Naked Gun 2 1/2 swimming in the sewage outlet.
You must just remember to rotate the rods in the right direction when pushing them down the pipe if you have the claw on the end, otherwise they will unscr*w and you are then in the deep doodoos.

Absolutely right, Malcolm . . . and keep turning in the same direction as you withdraw the rods.

Another thought for the day is that even the most mundane of manual operations requires a degree of intelligence.

https://m.youtube.com/watch?v=y_kGHFUjhI4
Just an example of a manhole tray cover carrying the surface material. Other examples are available.

Thank you so much for your help and to the other helpful readers for their advice. Much appreciated.

Luckily most built-up parts of the country are now covered by detailed and extensive mapping by specialist firms with access to the data and records of the utility companies and local authorities so they can produce digital maps centred on any property showing all sorts of interesting features, including, for a previous property in Norfolk, the underground pipelines that were installed in the lead up to and through the Second World War to supply aviation fuel to all the aerodromes dotted around the county. A new housing estate was built across the area but I noticed that the layout left an undeveloped space along the course of a pipeline and there were marker plates in place to identify it so no-one would start digging and burst the pipe.

The building is 9 floors and is above the 18-metre height threshold. It has no cladding, but painted rendering, behind which there is allegedly combustible insulation. And yes, I’m happy to follow up by e-mail.

I do wonder how the cost of waking watchers can be justified. I presume there are 500 flats to monitor with 3 shifts each doing 5 days. Has anyone asked for justification of the cost?

There are a few hundred flats, yes. They “work” 12-hour shifts at minimum wage, with a nice profit on top for the brother of the management company’s senior manager.