In most instances, damage to a property from escape of water will occur slowly over time. It is in fact very rare that damage will manifest itself in a more sudden manner. Generally, such damage is related to a water supply leak where the volume of escape is much more greater.
And this is the case for this property in Co. Kilkenny where a ‘sink hole’ and other structural damage occurred overnight due to a leaking water supply. A mains water supply was running through the rear extension and a leak had occurred on the saddle connection between the water main and the service pipe. The leak was repaired and the area made safe by a contractor working on behalf of the utility provider.
The damage to the property was extensive, particularly in the vicinity of the leak. Category 3 cracking, doors and windows sticking and floors sloping were all evident. Notwithstanding all that, damage to the extension warranted a complete rebuild. The requirement for demolition in subsidence claims are extremely rare.
Substruck Ltd. was employed by the insurance company to design an underpinning solution to address the damage. Site investigation was required which included trial holes and ground investigation in the form of dynamic probing.
The proposed solution was a micropile supported raft needled through the rising walls of the primary structure. This would protect both the walls and floors of the property. And the rear extension was to be provided with a new micropile supported raft foundation.
‘Drains and ‘sewers’ are terms used interchangeably in the industry; however, by definition, they are very different. Simply put, a drain is privately owned and a sewer is owned by the State.
Since 2014, Irish Water is now responsible for wastewater (i.e. foul water), although storm water remains the responsibility of the local authorities. Up to 2018, a private drain remained private up to the public sewer, regardless of where the drain was located. Therefore, the responsibility for that drain rested with the homeowner. If the drain was served by more than one premises, responsibility was shared on a pro rata basis. In the UK, assessing responsibility is much more complex.
So if a homeowner wanted to replace this drain due to simple wear and tear, they would have to employ a civil engineering contractor to obtain a road opening licence from the local authority and complete the works.
However, since the amendment to the Water Services Act (2007-2017), a drain becomes a sewer as it enters public property and is no longer the responsibility of the homeowner. But if that drain enters another private property, responsibility remains with the homeowner and not the neighbour!!! Access to that property to maintain your drain is provided under the Land And Conveyancing Law Reform Act 2009.
Therefore, Irish Water is now responsible for the pipework from the boundary of the property .
Great news for homeowners – bad news for the taxpayer!!!!
Water supply leaks can cause significant structural damage to properties, even over a short period of time. During a subsidence investigation at this property in Blackrock, Cork City, a private shared lead water supply was found to be the cause of the problem. Damage was noted as Category 2 cracking and enough distortion to render two doors permanently closed.
The leak was repaired and on inspection a hole with a diameter of 5mm was identified!!!!! This would suggest that the leak has been occurring for quite some time and the quantity of lost water must be enormous. The problem with old shared water supplies (which sometimes run to the rear of terraces) is that many are not provided with water metres. And therefore, leaks are more difficult to identify.
Lead has been used in domestic pipework in some houses up to the 1970s and the health effects are well documented. Irish Water estimate that about 180,00 homes and businesses are still being serviced by some degree of lead pipework.
The majority of lead water supply is inside private property which in theory places the onus of repair on the homeowner or homeowners. Irish Water offers a lead pipe replacement scheme which will replace any public side lead service connection pipes free of charge to customers if they have replaced the private side lead supply pipe. And grants are available to homeowners in certain circumstances.
At Substruck, we have been repairing and replacing all types of water supplies since we began trading in 2003. If you think you may have a lead supply and are interested in addressing this, please contact us for further information.
There are many anecdotal guidelines to when one should become concerned about a crack. The width of the crack is only one aspect of crack interpretation and even though you might not be able to put your hand through it, if you see daylight on the other side then its certainly time to become concerned.
The cracking on this blog is as a result of an extension built on a raft foundation in Galway City about ten years ago. The extension is rotating away from the original dwelling. It is in fact ‘tilt’ where the foundation or building moves as one unit with little or no cracking or distortion on the extension itself. Factors that influence the ability of a structure to tilt are the geometry of the building and the reinforcement of the raft. And of course, the ground conditions.
Tilt is normally expressed as a fraction and research by the Building Research Establishment have provided guidance on indicative values from where a building becomes noticeable (1/250) to where monitoring or remedial action (1/100) is required.
In this instance, a trial hole revealed that the raft was built on fill which was poorly selected and placed. Unfortunately, there was no supervising engineer employed for the works and the builder was allowed to design and construct the foundation himself.
The term ‘filled ground’ is used loosely in the construction industry but it has a very specific meaning. BS5930 Code of Practise for Ground Investigations defines such ground as that ‘in which material has been selected, placed and compacted in accordance with an engineering specification’. Ground that that has been simply filled without any engineering control is termed ‘made ground’. Both types of ground are generally termed ‘anthropogenic’ as man has had an influence over both.
In most instances, anthropogenic soils derived from sampling or trial holes can be easily identified as either filled or made ground. And this is certainly the case at a property in North Cork where made ground was identified as the culprit to foundation movement in a residential property. Although the soils are clearly re-worked, a few bottles here and there prove that the soils have been made up with little or no control.
Dynamic probes show that the soils were poor to depths of 1.5m to 2.5m with refusal encountered at about 3.5m. Considering that the foundation was constructed to greater than normal parameters, it could be the case that the builder / engineer on site increased the dimensions to compensate for the poor soils. Nonetheless, it didn’t work and the proposed solution is a combination of raking micropiles through foundation and ground improvement.
The ability of masonry to arch (or ‘self-arch’) relates to the transfer of axial loads above openings to either side of the wall and is considered during lintel design. The term comes from the principle of how an arch works although there is in effect no arch (if that make sense).
For arching to occur, the main criterion is the presence of sufficient masonry above the apex of a 45° isosceles triangle, formed above the opening. Other factors include the bond pattern, location of movement joints and the ability of the masonry on either side to carry the loads.
In underpinning works, the arching action of masonry is considered when specifying centres of needle beams in micropile supported raft foundations and traditional pile and beam systems where beams are to be installed through rising walls.
However, foundation movement to the order of about 50mm has rendered this garage wall in Co. Laois cantilevered along a combined length of about five metres and defying the laws of gravity!!!! The walls are constructed of cavity block in the normal overlapping bond pattern with no opes or movement joints to limit a uniform load distribution.
Ground investigation showed that the building was partially constructed on made ground to a depth of about two metres. According to the homeowner, this area was made up during the construction of the primary dwelling with little or no controls in place. The surface water system was also poorly installed and contributed to the movement.
Construction sites are not always level and the design of economic foundation solutions to the engineer can be quite challenging.
In gently sloping sites, strip foundations may be stepped. However, where there is a more appreciable change in gradient, a cut and fill process can be adopted where the higher level is cut away and the lower level is filled. In some cases, the cut area is used to fill the lower area if the soils are appropriate.
If the cut soils are not appropriate, engineered fill will be required. This is where selected fill is placed and compacted to an engineer’s specification and carefully monitored to ensure that it can act as a suitable support for the new foundation.
This dwelling, built about fifteen years ago, has a raft foundation constructed on a cut and fill site, with half the building founded on the cut side and the other half founded on the filled side – this ‘design’ is known as feather edging and carries risk. The drawings suggest that the whole footprint of the building was cleaned down to the rock and filled with ‘rolled broken rock’ to a depth of about two meters in the fill side and about 300mm on the cut side.
It is important to note that it is differential settlement in a building rather than uniform settlement than results in foundation failure. Raft foundations should be constructed fully on natural ground or fill of uniform thickness. Raft failure will occur in one of two ways: geotechnically, where it will tilt (as one unit) in one direction, or structurally, where the raft will break, and superstructure cracking will result. The factors that effect this include the reinforcement of the raft and the geometry of the building.
In this case, the raft has structurally failed, due to differential settlement of the fill.
The Building Research Establishment states that ground is the greatest hazard to any building, despite the fact that it is not always paid the degree of respect it deserves. For any significant building, sufficient investigation is required to determine if a ‘standard’ approach to foundation construction can be adopted or if a more specialist approach is required.
Some clients are not willing to pay for appropriate ground investigation as they cannot see the value in it. This may be more common where clients opt out of the statutory certification for one off properties or larger extensions.
One of the major risks with poor ground investigation is foundation problems post-construction and this is the case at this property in Cork City. Ground investigation was completed by someone who clearly didn’t have a clue what they were at.
Substruck was subsequently employed to provide data in relation to the ground conditions. Two number dynamic probes were completed in the area of distress and two number close to the original property, known as controls, where no distress was evident.
The results were clear. The probes along the area of distress identified soils of negligible bearing capacity. The hammer dropped under ‘self-weight’ for a distance of 400mm at both locations at depths of between 1 and 2. 5metres – this indicates very soft soils with bearing capacity of less than 10Kn/m2!!! The remaining blow counts were 1 over 100mm and 200mm until refusal was encountered at 3-3.5m!!!! In fact, it was one of the worst set of results that we have seen in quite some time.
In this instance, a piling solution would have been recommended. Unfortunately though, for all stakeholders, this is too late.
During site surveys of properties suffering from foundation movement, we always encounter other building problems. In this house, there was a concerning amount of mould growth in some areas of the building. Mould growth can trigger significant respiratory problems for the young and elderly, particularly those with asthma.
Mould growth is caused by condensation and condensation is caused by the presence of too much moisture in the air. Mould growth will occur if the relative humidity remains above 70% but will grow at an increasing rate at over 80%. High relative humidity results in condensation at higher internal air temperatures.
Condensation can be prevented or at least controlled by consideration of four factors – moisture generation, ventilation, heating and insulation.
In this bathroom, there was no extract ventilation – Building Regulations requires that all bathrooms are fitted with mechanical extraction of 15 litres/second minimum. Although, we did not enter the attic space, it is most likely that there is little or no insulation either.
In the bedroom, the likely cause is poor background ventilation and poor insulation in the attic. The vent is partially blocked on the outside after the walls were re-dashed some while back. Building Regulations require a minimum background ventilation of 5000mm2.
In many dwellings where resources are limited, condensation can be reduced by simple behavioural patterns and DIY works such as opening windows during showers (purge ventilation) and leaving them open for about 15 minutes after, not drying clothes on radiators and ensuring vents from dryers are connected to the exterior of the building.
Building on filled ground needs the careful selection of fill and controlled placement to ensure an adequate foundation material. However, secondary structures such as domestic garages and boundary walls, do not always get the respect they deserve. Structures built on the edge of filled ground, like this one in Co. Cork, require extra attention due to the risk of slip.
Like any works, the engineer must provide a specification and the builder must build to that specification. This must include a methodology for the placing and compacting of the fill including the type and mass of compaction plant required, the layer thickness and the number of passes. Typical layers would be about 200mm and should not vary by more than 15% to minimise the risk of differential settlement. Topsoil, any unsuitable material and other geohazards must be removed before filling can commence. Homebond state that ‘filling and compaction should be carried out under the supervision of an engineer. The engineer appointed should be qualified by examination, be in private practise and possess professional indemnity insurance.’
It is important to note that it is differential settlement in a building rather than uniform settlement than results in foundation failure. Raft failure will occur in one of two ways: geotechnically, where it will tilt (as one unit) in one direction, or structurally, where the raft will break, and superstructure cracking will result. The factors that effect this include the reinforcement of the raft and the geometry of the building. In this case, the raft has structurally failed, due to a combination of landslip and excessive settlement of the fill