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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.

Crack at Gable 1 A

Crack at Gable 1 B

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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.

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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.

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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.

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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

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One might imagine that any new dwellings presented to the market would be compliant with Building Regulations. However, this might not always be the case and some high profile failures such as Priory Hall and Longboat Quay provided more than enough evidence to government that things had to change.

Up to 2014, professionals would only need state, through non-statutory Certificates of Compliance that, in their opinion, the building substantially complied with Regulations. Furthermore, independent inspections were not mandatory. To address this, the government introduced the Building Control (Amendment) Regulations 2014 which introduced new controls including mandatory site inspections and certification.

Some construction (and design!!!!!) during the boom was poor and an embarrassment to our industry to say the least. Substruck were employed to complete a homebuyers drain test at a ‘new’ residential property in Co. Cork. This was in effect completion of units in an unfinished ‘ghost’ estate so BCAR did not apply. However, the Building Regulations still did.

In drainage investigation, you can always judge a book by its cover. Before any testing or CCTV equipment was brought onto site, direct observation showed us that the construction of the drains was pretty poor, both in terms of compliance with current Building Regulations and good practise.

The photos show how the drainage was finished at ground level during more recent patio works. And I think they speak for themselves. It is clear that no test was completed on the drains either during the original drainage works or the remaining completion works. Out of five sections, one passed, while two could not be tested due to the absence of any access points!!!!

This was just one series of defects identified in the survey. Others included absence of access to a WC, trip hazards, a hole in the drain to accommodate a new gully, deformation, open joints and water holding.

BCAR is not without its weaknesses and these were identified in the Oireachtas report ‘Safe as Houses? A Report on Building Standards, Building Controls & Consumer Protection’ in 2017. However, it is still a huge improvement on the previous regime and should help to significantly reduce this type of workmanship.

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H1 – A building shall be provided with such a drainage system as may be necessary for the hygienic and adequate disposal of foul wastewater from the building.

H2 – A building shall be provided with such a drainage system as may be necessary for the adequate disposal of surface water from the building.

H3 – No part of a drainage system conveying foul wastewater shall be connected to a sewer reserved for surface water and no part of a drainage system conveying surface water shall be connected to a sewer reserved for foul wastewater.

Above are the three Building Regulations for the design and construction of drainage works in Ireland. The purpose of these Regulations is to provide for the safety, health and welfare of persons and the protection of our environment. They are very broad statements (particularly the first two) which are supplemented by Technical Guidance Document H – Drainage and Wastewater Disposal. Therefore, if works are completed in accordance with this document, that will, prima facie, indicate compliance with these Regulations. However, there is very little other guidance required (you might think) for the third and final Regulation, which simply does not allow cross connections (or mis-connections) in drainage systems. This is where householders and builders inadvertently (I would hope) connect household appliances to the wrong drain, i.e. surface water. On the other hand, surface water entering foul waste water system will increase pressures at sewage treatment plants.

Most properties have two drainage systems – foul wastewater from bathrooms and kitchens and surface (or storm) water from the roofs and driveways. In other words, any dirty water should go to the foul system and any clean water should go the surface water system. Considering that the surface water is drained to local watercourses, the EPA have identified cross connections as a significant contributor to the deterioration of the water environment in our country. Cross connections are deemed an offence under Section 3 of the Local Government (Water Pollution) Act, 1977, and Section 16(7) of the Local Government (Water Pollution) Act, 1977. And, it is up to the homeowner to rectify any cross connections!!!!!

Buildings undergoing renovation works, like this property in Co. Cork, are at most risk of cross connections. The renovation of a garage required the relocation of various appliances. The first cross connection was from a washing machine which was drained to a surface water gully at the corner of the property. The second and third cross connection was where sink waste and condensate from the boiler was drained to a second surface water gully.

If you have any concerns re cross connections, please feel free to contact us and we can survey your drains to ensure that everything is going where it is supposed to go.

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Newly constructed buildings will nearly always be vulnerable to cracking for a variety of reasons. However, nowadays we understand much more about why this occurs and what particular controls can be put in place to minimise the effects of movement of building materials and components.

Shrinkage will occur in masonry structures, particularly if blockwork has not cured properly. However, the secondary control to accommodate this shrinkage is the installation of a movement joint.

Movement joints are generally formed to address either contraction (shrinkage) or expansion, whichever will occur first. These terms are used interchangeably in the industry although they are very different. For example, movement joints in concrete footpaths are often referred to as ‘expansion’ joints although they are in effect ‘contraction’ joints as contraction will always occur first as the concrete cures and loses its moisture content.

Unfortunately, buildings can be designed or constructed poorly, with less regard to these controls as identified in the Technical Guidance Documents or Homebond manual.

This crack has formed in the middle of two semi-detached houses in Ballyvolane, constructed in 2005. It is mirrored on the opposite side of the building which is to be expected. The whole building is about 16m in length and 6m in width. It is clear that a movement joint has not been installed and could have been neatly concealed behind the downpipe.

Homebond provide good guidance for movement joints in both brick and masonry buildings. It states that ‘Codes of Practice recommend that spacings of movement joints should be referred to by the building designer. It is not standard practice to incorporate movement joints in semi-detached houses. Based on traditional construction, the minimum recommendation is that in terraces of three or more houses, joints should be built in every two houses unless specified more frequuently by the designer.’ (Homebond, 2008). It also refers to joints at 12m centres or very two houses whichever is less.

Considering the geometry of this building, a movement joint should have been installed. As cracking will normally occur over weak points in a building, it was just unlucky for this homeowner that it occurred on his side.

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Subsidence monitoring can take many different forms; from simple measurements with a crack gauge to continuous recordings with a wireless crack movement recorder, with built in data logger. Each system comes with its own strengths and weaknesses, which must be considered in order to apply the most appropriate and effective technique.

Crack monitors or ‘tell-tales’ are the most common form of subsidence monitoring used in Ireland. They are easily sourced online so anybody with a VISA card and a drill can install them. And that sometimes is the problem.

The cheaper alternatives do not possess pre-set pegs which allow for quick and easy fixing. However, the pre-set pegs do not always allow the cursor to be square to the grid so accurate recording on installation is paramount. This can occur on uneven finishes such as wet dash or where lateral movement has taken place.

To be fair, standard tell tales (without the pre-set pegs) require a bit more thought and this wasn’t applied on a property in Roscrea, Co. Tipperary where readings from crack monitors would suggest that all cracks have closed by a distance of over 25 mm!!!!!

This is just one example of how poorly installed and recorded monitors provide no data whatsoever and can be a complete waste of time and money for the consumer. Subsidence monitoring should be performed by qualified, experienced professionals for accurate results –

Substruck Ltd. is an approved installer of Avongard crack monitors.

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Foundation movement can affect the serviceability of a building. This may include water penetration through cracks and sloping floors. It can also result in distortion of door and window frames. This can be as an indirect result of movement in the external walls or directly through movement of the internal walls. 

Such movement can take the form of ‘wracking’ where the frame loses its squareness (if that’s a word) and is demonstrated by tapered widening at one end of the gaps and a narrowing at the others. This results in the door jamming. The most common cause of doors jamming in older properties is normally temperature and moisture variations during the year.

This door frame in Cork City is about 20mm out of level!!!

But, interpretation of movement needs careful consideration. In this instance, it is evident that the top rail of the door and architrave have been significantly altered over a long period of time and this is disproportional to the cracking. This would suggest that the initial movement began quite some time ago, maybe when the building was constructed, and adjustments were made from or at that point.

Nonetheless, movement was rejuvenated for another reason thereafter and the result was a development of the original movement. This is demonstrated in the cracking. The weak points in the superstructure created during the settlement period will normally be the first to be compromised.

Therefore, it could be argued that the distortion in this situation represents both settlement and subsidence.