Best way to insulate solid 9 inch wall with no DPC?

[Matthew309]

So the cistern is on the upslope side of the house? If so, then the black pipes, which at 1metre underground are presumably situated below the clay bed, may be routing the water to soakaways in the surrounding land. In which case surface rainwater must be entering from upslope and the only available route would be from an old French drain situated above the clay bed and directed toward the cistern.


Considering the cost, effort, materials and time needed to do that I would suggest that a French drain - sited a few meters away beyond the edge of the concrete outdoors - as per my previous suggestion - would be far less expensive and troublesome.

So I've double checked the black pipe. It appears to be made out of thick cast iron or something. When I check the level of it it appears to slope into the cistern. But on camera it goes off around 10 meters then to the left, away from house house and towards the public path/neighbours. It points in the direction of an old air raid shelter but I've since removed that and never saw and pipes in it.

 

[Cubist]

Regardless of where this cistern is located one or even both the black pipes may indeed dbe intended to carry overflow from the cistern to some other location and it would be reasonable to assume that these connect either to a soakaway or some other storage tank/cistern elsewhere on or off the property - without some kind of pumping system they cannot be for anything else.

The only relevance this cistern has to your problem is that it may, IF it is located on the uphill side of the house, offer a simple and easy to access means to divert rainwater run-off away from the house.

 

[CliffordPope]

The only relevance this cistern has to your problem is that it may, IF it is located on the uphill side of the house, offer a simple and easy to access means to divert rainwater run-off away from the house.

Is there anywhere on the property at a lower level than the water in the cistern?
If so, sink a pipe round to the lower point and the water would drain away.

 

[Matthew309]

Regardless of where this cistern is located one or even both the black pipes may indeed dbe intended to carry overflow from the cistern to some other location and it would be reasonable to assume that these connect either to a soakaway or some other storage tank/cistern elsewhere on or off the property - without some kind of pumping system they cannot be for anything else.

The only relevance this cistern has to your problem is that it may, IF it is located on the uphill side of the house, offer a simple and easy to access means to divert rainwater run-off away from the house.

Is it wise to drain this cistern to maybe an extra meter down at all times? That would certainly reduce hydrostatic pressure in the vicinity, however my concern would be the clay would dry excessively and cause subsidence, especially considering how much the building has already settled

 

[Cubist]

You still have not told us where this cistern is located. Is it uphill or downhill from the house?

The first photo of the cistern you shared shows the water level well above the two large diameter black pipes and there seems to be an immersed pump too.

If the cistern is sited above the house then the depth of the water in that photo strongly suggests the foundations and the concrete slabs are 'foot wet'. If it is on the downhill side then there is a chance the foundations and slabs MAY be dry and reasonably safe.

Irrespective, its clear that one or more of the following conditions obtains: -

• One or both of those black overflow pipes are either obstructed or completely blocked OR
• The land below, to which these pipes flow, is so water sodden it cannot accept any more water draining from the cistern.
• Emptying the cistern is unlikely to produce much in the way of benefit as its contents could represent the 'high tide mark' for the body of water represented by ALL the water flowing down the hill above the clay layer - during periods of heavy and consistent rain the pump would be permanently running and to no advantage.

There is a further consideration insofar that the water flowing down the hill will inevitably be carrying away some of the looser materials from above the clay layer together with washing some of that clay out. This can, if not properly managed, lead directly to the subsidence you mention.

I'm afraid your best, and to my mind only, strategy is to either thoroughly repair/enhance the extant or install a new drainage system.

 

[Matthew309]

You still have not told us where this cistern is located. Is it uphill or downhill from the house?

The first photo of the cistern you shared shows the water level well above the two large diameter black pipes and there seems to be an immersed pump too.

If the cistern is sited above the house then the depth of the water in that photo strongly suggests the foundations and the concrete slabs are 'foot wet'. If it is on the downhill side then there is a chance the foundations and slabs MAY be dry and reasonably safe.

Irrespective, its clear that one or more of the following conditions obtains: -

• One or both of those black overflow pipes are either obstructed or completely blocked OR
• The land below, to which these pipes flow, is so water sodden it cannot accept any more water draining from the cistern.
• Emptying the cistern is unlikely to produce much in the way of benefit as its contents could represent the 'high tide mark' for the body of water represented by ALL the water flowing down the hill above the clay layer - during periods of heavy and consistent rain the pump would be permanently running and to no advantage.

There is a further consideration insofar that the water flowing down the hill will inevitably be carrying away some of the looser materials from above the clay layer together with washing some of that clay out. This can, if not properly managed, lead directly to the subsidence you mention.

I'm afraid your best, and to my mind only, strategy is to either thoroughly repair/enhance the extant or install a new drainage system.

The cistern is located on the upside of the house. One black pipe comes from the gutter so rain water feeds into it. The second deeper black pipe aims downhill, but according to my level, still runs INTO he cistern ( ie it's sloped towards it).


There is NO concrete slab as such, it's just internal flooring but does not sit under the load bearing walls which are directly on the soil. So yes the the foundation are saturated fully.

I can add drainage but it's going to be very difficult diverting it, unless I dig a HUGE soak away near the public foot path as the only location for it is in the garden which is already utilised by the gutter the other side.

 

[Cubist]

The second, lower, black pipe is undoubtedly the overflow from this cistern. With no means to pump water FROM the cistern through this pipe it cannot be anything else unless there is a FEED into that pipe from elsewhere.

As the cistern is on the uphill side of the house the depth of the water you have seen is the very worst case scenario as the actual groundwater level MUST be below this. Nevertheless rainwater runoff from the hillside will be collecting against the foundation and will be penetrating under the concrete floor slabs on the ground floor. These slabs will be protected by the DPM provided they are not damaged.

You do not need to construct a soaraway of any size. ALL that is required is that you install a French Drain along the rear and both sides of the house to direct groundwater runoff away from the foundation. The land further down the hill will do the rest.

 

[Matthew309]

The second, lower, black pipe is undoubtedly the overflow from this cistern. With no means to pump water FROM the cistern through this pipe it cannot be anything else unless there is a FEED into that pipe from elsewhere.

As the cistern is on the uphill side of the house the depth of the water you have seen is the very worst case scenario as the actual groundwater level MUST be below this. Nevertheless rainwater runoff from the hillside will be collecting against the foundation and will be penetrating under the concrete floor slabs on the ground floor. These slabs will be protected by the DPM provided they are not damaged.

You do not need to construct a soaraway of any size. ALL that is required is that you install a French Drain along the rear and both sides of the house to direct groundwater runoff away from the foundation. The land further down the hill will do the rest.

So even thought the pipe is leveled for floor toward the cistern your saying it's an overflow?

Unfortunately, downhill from my house is two other houses, one very large one direct behind, then another on the other side of the footpath. To the only place what could ever get downhill would be exit the french drains onto the footpath, which is far from ideal.

Something I also noticed is during heavy rain the low point with it in between those two properties is where the water pools, that also happens to be the foul drain lid, so the excess water likely accesses the foul system due to pressure on the lid leaking. Additionally, his house had to be underpinned in the past.

Topologically it's a very difficult area to work with as it's rural but there's nowhere to direct surface water without causes negative consequences to someone else's property.

 

[Cubist]

So even thought the pipe is leveled for floor toward the cistern your saying it's an overflow?

No one but a bloody idiot would build a cistern/well on the uphill side of a house without providing some means for overflow to be directed elsewhere. However, there have always been bloody idiots around but the house clearly has a long history during which a smarter owner would have spotted this omission and corrected it.

Topologically it's a very difficult area to work with as it's rural but there's nowhere to direct surface water without causes negative consequences to someone else's property.

That's an unfortunate fact of life and chance that no-one can control.

The thumbnail photo of my house, on the left, doesn't tell you that it is situated on a hill-side in a small valley. The foundations are circa 20feet above the valley floor and the ridge of the hillside is 100-150feet above these and around 250yards from the house. The slope angle of the hillside is 45-60 degrees and the land has a fairly deep top-soil layer above a clay bed and below that a limestone and granite bed rock.

Until I modernised and improved the French Drains protecting this place to enhance their performance parts of the house would be flooded with rainwater run-off from that hillside.

You are in exactly the same situation. Unless you divert the run-off from the hillside behind your house it will continue to be damaged by that water AND that water will then continue down the hill from your house to perhaps affect your neighbours. You cannot control that result and nor can you make it any worse - to think otherwise is utter nonsense.

 

[Cubist]

A further point I forgot to mention and concerning the apparent angle of the black pipes in the cistern.

Subsidence and 'Land Heave' can result in movement and breakage of underground pipes. Subsidence results from the top-soil becoming too dry and losing its structure and collapsing. Land heave is an upward shift of the soil and typically results from the clay layer becoming too wet. Both of these phenomena frequently result in damage to and breaks in underground pipes and services as well as damage to the structure of buildings.

 

[Matthew309]

A further point I forgot to mention and concerning the apparent angle of the black pipes in the cistern.

Subsidence and 'Land Heave' can result in movement and breakage of underground pipes. Subsidence results from the top-soil becoming too dry and losing its structure and collapsing. Land heave is an upward shift of the soil and typically results from the clay layer becoming too wet. Both of these phenomena frequently result in damage to and breaks in underground pipes and services as well as damage to the structure of buildings.

Update regarding black pipe (the other is from the gutter and is an input). The cistern water level raised last night and bubbles produced from water trickling in would be gently pulled through that lower black pipe. This is apparent that although that angle is into the well, the average angle is downhill. Therefor is evident that the black pipe is some form of overflow.

I'm not confident it doesn't have any splits or damage so will be looking int a survey. If this is an overflow which has an exit lower down the hill, could i input my French drain into the cistern and utilise this overflow ?

as the black pipe is only 40-50cm below ground level, could a small pump to reduce it further to say 1m might be better to keep hydrostatic pressure along the upside edge of the house down and help prevent damp being pushed into the footings?

 

[Cubist]

I think a simpler and less costly solution would be to divert the water from the roofs gutters to discharge to the sides of and downhill from the house rather than directly into this cistern.

This alone would vastly reduce the total volume of water to be handled by the cistern and its extant overflow pipe. Perhaps to a bare minimum consisting only of the groundwater from the hillside directly above the house. This new maximum level of water could then be monitored to ensure that either it never reaches the overflow outlet or, should it do so, that the overflow pipe can handle the required excess volume of waste water.

If you then find that the cistern continues to overfill well beyond the height of the overflow pipe only then would action to investigate the pipes condition and remedy any faults become essential.

While pondering this issue it occurred to me that this cistern and its overflow pipe were probably installed as an immediate precursor to construction of the house. A cast iron pipe would have been an expensive investment that could have been very easily avoided. Was your house part of an estate operated by the owners of the large house further down the hill? If so, I suspect that this overflow pipe may be a feed directly to that large house or maybe to an intervening pond or small lake perhaps used for fishing.