Public foul gravity sewer directly under house help please

Section62

Grumpy_chap said:

I wonder whether that sewer location pre-dates the houses being built in Pinewood Close and the sewer was actually diverted before the road was constructed by the mapping information for the sewer never got updated.
Certainly, today, the developer would not be permitted to construct without diverting the sewer first.

As I suggested upthread, there's probably a good chance the true route is more complicated than the dot-to-dot plan shows - for example there could be another chamber in each of the front gardens of 10 and 1 so the pipe runs under what I assume are garages with a dog-leg between them.

Another possibility is the sewer is deep - 600mm concrete pipes could be jacked or installed in heading - in which case there may be less concern about building over them.

There is another possibility that the large diameter pipes were installed for storage as part of a flood relief scheme - the size doesn't always equate to how important the sewer is.

GDB2222

Section62 said:

Grumpy_chap said:

I wonder whether that sewer location pre-dates the houses being built in Pinewood Close and the sewer was actually diverted before the road was constructed by the mapping information for the sewer never got updated.
Certainly, today, the developer would not be permitted to construct without diverting the sewer first.

As I suggested upthread, there's probably a good chance the true route is more complicated than the dot-to-dot plan shows - for example there could be another chamber in each of the front gardens of 10 and 1 so the pipe runs under what I assume are garages with a dog-leg between them.

Another possibility is the sewer is deep - 600mm concrete pipes could be jacked or installed in heading - in which case there may be less concern about building over them.

There is another possibility that the large diameter pipes were installed for storage as part of a flood relief scheme - the size doesn't always equate to how important the sewer is.

If it’s deep, does that reduce the chance of something going wrong with the sewer? 

If it’s a trunk sewer, and bear in mind that the diameter increases a bit further along, is it even possible to divert it? Whilst the works are taking place, what happens to all the contents that normally flow through? And installing a dog leg would significantly reduce throughput, perhaps? 

jojoxxx2001

Thanks all will definitely look into everything suggested.

The area isn't hilly ...I didn't even notice the manhole !!! The field at the bottom of the garden are school playing fields so maybe provide access ..but definitely will look into deeds

The estate is probably around 1970 build

35har1old

Section62 said:

GDB2222 said:

GrannyKate said:

Worth knowing where it is exactly because of potential future developments.  When we had our extension built 12 years ago the building inspector had quite a few conditions relating to the sewer if it stayed where it was but recommended the best course was to move it out of the new property line so it would be under the new patio not under the bungalow.  Cost about an extra £1000 I believe. 

You can do that with your own drains, but can you do it with a public sewer?

You can ask the sewerage undertaker to divert a public sewer - they may agree to allow you to do the work yourself, or may want to do the work and bill you for it.  In a few cases (mainly with major or trunk sewers) there isn't an option to divert.

But it is usually an expensive business, and on a domestic scale the costs can easily be out of all proportion to the value of the property.

Looking at the drawing there doesn't same to be any room within the property boundary to divert also you would be extending the run of the sewer and might have insufficient fall in the sewer
4 inch sewer max 1in 40 fall
6 inch sewer max I in 60 fall

Section62

35har1old said:

Section62 said:

GDB2222 said:

GrannyKate said:

Worth knowing where it is exactly because of potential future developments.  When we had our extension built 12 years ago the building inspector had quite a few conditions relating to the sewer if it stayed where it was but recommended the best course was to move it out of the new property line so it would be under the new patio not under the bungalow.  Cost about an extra £1000 I believe. 

You can do that with your own drains, but can you do it with a public sewer?

You can ask the sewerage undertaker to divert a public sewer - they may agree to allow you to do the work yourself, or may want to do the work and bill you for it.  In a few cases (mainly with major or trunk sewers) there isn't an option to divert.

But it is usually an expensive business, and on a domestic scale the costs can easily be out of all proportion to the value of the property.

Looking at the drawing there doesn't same to be any room within the property boundary to divert also you would be extending the run of the sewer and might have insufficient fall in the sewer

As I said, "In a few cases (mainly with major or trunk sewers) there isn't an option to divert".  The size of the pipe in this case suggests that it is a strategic or trunk sewer so diversion would be less likely to be feasible than in the average domestic setting.

There is no reason why the diversion has to be "within the property boundary", although in this case the options are limited by the density of the housing development.  If the diversion needs to be outside the property boundary then as a statutory undertaker the water company has powers to acquire rights to lay the diverted sewer in other land.

But diversion of this sewer (even if it were necessary) is unlikely to be feasible as the work may end up costing more than the house is worth.

35har1old said:

4 inch sewer max 1in 40 fall
6 inch sewer max I in 60 fall

These are falls for small diameter pipes.  The pipe under this property is 600mm (24") going into 675mm (27").

The minimum falls on small diameter pipes are set to provide for self-cleansing velocity given the intermittent flow found in small-diameter foul sewers.

For larger diameter pipes being used in normal circumstances the considerations are different.  You would expect the flow in a 600mm pipe to be continuous and even in dry weather for it to be flowing at half-bore or more.  Depending on the pipe material, SCV could potentially be achieved with falls in the region of 1:1000.  There is a fair bit less sensitivity to reduced falls when dealing with sewers of this kind of diameter and probable flow rate. So the limiting factor on whether a diversion was feasible is unlikely to be the available fall.