76 The categories referred to being those set out in Appendix C of the 96 Standard where Category 1 is wall cracking less than 1mm and Category 2 less than 5mm (as a result of the movement of the footings).
77 It is interesting to note that the same clause in the 88 Standard, Clause 1.3, had a similar statement as to the performance objective, however it was more specific as to the level of performance that needed to be achieved, stating that an acceptable probability for excessive foundation movement on a normal site was 5%, that the design life of a dwelling may be taken as 50 years and 'significant damage in walls' is cracks greater than 5mm.
78 Mr Neil considered that a significant cause of the most substantial cracking near the front façade and in the garage walls including the party wall was due to the trees planted by the builder at the front of the property as the damage had not started to occur until some three years after construction. He considered that if existing trees were the most substantial cause, the cracking would have started earlier. A further factor pointing to the trees planted in the front of the premises being the substantial cause of the cracking at the front of the building was that the existing trees on the east side of Evansdale Road are the furthest away from the south-west corner of the building, yet this is where the greatest settlement took place. Mr Neil says that the trees, particularly the line of pears on the south side of No. 59, provide a satisfactory explanation for the differential settlement observed at the south-west corner of No. 59. He considered that the other substantial cause was that the footings were not constructed in accordance with the engineering drawings which specified a minimum depth of 850 and in the area of the concrete pier at the west end of the party wall had been measured at 650mm and on the west side of the alcove to No. 59 had been measured at 600 and on the west side of the alcove at No. 57 it had been measured at 900mm. He gave evidence that the strength of a footing varies as the third power, ie the cube, of the depth of concrete, therefore, the reduction in the depth of the concrete from 850 to 650 meant that the footing's stiffness was only 45% of the stiffness that would be given by a footing at the specified depth of 850mm, if the concrete depth was 600mm the stiffness would only be a third of the design value. He also considered that the failure to have a cut-off or Ag drain near the base of the footing across the western end would allow sub-surface water and any surface water that escaped from the grated drain to cause an area of increased moisture in the soil against and immediately below this footing. This wetter zone in the soil would also attract tree roots to the area so that in dry times the soil moisture reduction would be accelerated over the drying of the surrounding soil, unaffected by tree roots, thus causing increased settlement of the founding soil under the footings in this area. He acknowledged that the collection of water against the footing may encourage some heave but the tree roots would substantially reduce the amount of moisture. It should be noted that MacGregors commented on the presence of tree roots when they investigated the depth of the footing and the soil conditions at the central pier at the west end of the façade at the western end of the party wall.
79 Mr Neil considered that most of the vertical cracking in the party wall behind the garages was probably due to the shrinkage of the concrete blocks.
80 Applying the 96 Standard Mr Neil considers that the architectural draftsmen should have considered sub-surface drainage as a design should not allow water to collect against the footings. The engineering design prepared by the structural engineer using the 96 standard anticipates normal moisture conditions for the design to apply and it was the architectural draftsmen in preparing the plans that drew all of the other practitioner information together to ensure those normal soil moisture conditions are achieved.
81 Mr Neil considered that a further factor pointing to the trees planted in the front of the premises being the substantial cause of the cracking at the front of the building was that the existing trees on the east side of Evansdale Road are the furthest away from the south-west corner of the building, yet this is where the greatest settlement took place. Mr Neil says that the trees particularly the line of pears on the south side of 59 provide a satisfactory explanation for the differential settlement observed at the south-west corner of No. 59.
82 Mr P. Haworth made four points. Firstly he considered that the performance of the masonry in the eastern half of the dwellings was performing satisfactorily in relation to cracking and vertical level. Secondly, he considered that there had been some heave in the area of the lightwells due to water getting into the open lightwell areas.
83 He also considered that water was flowing from the subfloor of one property to another through the hole in the footing wall to the east of the lightwells. Secondly, he did not consider the trees at the front had a large affect. He did not consider that the large eucalyptus on the west side of Evansdale Road approximately opposite No. 57 were having any effect as they were not damaging nearby existing houses. Thirdly, he noted that the footings of the outrigger entrances with their re-entrant corners were not tied back into the main footing grid of the building as required by the 96 Standard for re-entrant corners. This meant that the footing system did not have sufficient structural rigidity to resist any movements of the entrances and is why the cracking and rotation is evident at both entrances.
84 Fourthly, he considered that the footings were undersized often with only 600mm depth of concrete and they are not complying with the engineering design. Mr Haworth disagrees that the architectural plans should show a cut-off drain across the western end of the dwellings. He does not consider that the architectural draftsmen should be aware of the requirements of the residential slabs and footing standards. However, Mr P. Haworth agrees with Mr R. Neil that it was prudent to put a cut-off drain in front of the western footing to keep moisture away from the zone of the founding soil.
85 Mr R. Brown considered that the eucalypts on the west side of Evansdale Road were significant and were drawing moisture from under the house, he considered that the whole site had been dry to start with, ie after the removal of the previous house. However, later in the hearing Mr Brown submitted that, although initially he didn't consider that the tree planting at the front caused any substantial problem, he now considers that they could as he had examined photos of them before their removal and they were substantial and vigorous. He considered that the primary mechanism for the damage by cracking to the part of the building was heave at the rear of the garages. He considered the slope in the levels as shown by all of the engineer's floor levels was nothing more than a builder's intention to ensure the garages drained out the main door and the concrete floor slabs did not pool water. He considered that the water source for the heave is the broken outlet to the garages grated drain in No. 57 and that the water that escaped from the drain runs along the top of the strip footing and along the party wall to the rear of the garage of No. 57 where it causes the heave. He agrees that the footings do not have sufficient depth of concrete in many locations and considers that probably clay fell into the trench, prior to or during the pouring of the reinforced concrete footings. He considered that the rear of the house is performing satisfactorily but that a lot of the damage is caused by a lack of sufficient or proper masonry control joints.
86 Mr Bolwell considers that the settlement along the western façade of the building is most likely due to bearing failure of the founding soil, by which he means that the soil strength beneath the footing is so low due to its moisture content that it fails to support the footing and the loads placed upon the footing. This indicates a water source that Mr Bolwell considers could be a leaking stormwater drain or sewer. Mr Bolwell subsequently organised a camera inspection of the sewer pipes serving the dwellings but no leaks were found.
87 In the engineer's discussion, Mr R. Neil put to Mr R. Brown that the levels taken by the various engineers in their floor survey had shown settlement and not heave. Mr Neil said if it was heave one would expect that a water source would have been identified. Mr R. Brown said that the break in the grated drain immediately in front of the garage could be that source with water flowing along a pipe trench to the back of the garage. Mr R. Neil said how could the mechanism be heave if there was no difference in the level of the garage slab and the level of the timber floor at the door from the garage of the dwelling. Mr P. Haworth agreed that they were level. Mr R. Neil submitted that if there had been a degree of heave proposed by Mr R. Brown, about 10 to 20mm, it would have shown structural damage over time but after the initial major cracking in the front third of the dwellings, the cracking had remained largely the same. Mr R. Brown's response was that the garage slabs were infill slabs and were not attached to the footings and could move independently of the walls in the footing. Mr R. Neil responded that if the mechanism was heave you should see a step or significant difference in level at the garage door between the level of the timber floor immediately inside the dwelling and the level of the concrete garage slab at the garage door. Mr Neil also observed that if the drainage water was escaping from the grated drain and running down the side of the footing and into the founding soil beneath the footing, it is at this location that you would expect heave, but this is the location of the lowest relative levels and; therefore, presumably, the least heave.
88 Mr W. Bolwell disagreed that it was heave as he said the soil is not strong enough to lift the significant elements of the structure without failing and he considered the soil had already failed causing the major cracking at the front of the structure.
89 Messrs Brown and Bolwell considered that earth loose on the surface or from the sides of the footing trenches could have been knocked into the trench prior to the pouring of the concrete and this contributed to the lack of required concrete depth in the footings. But to get the concrete depth reductions that have been seen would need a consolidated depth of the loose fill of approximately 200mm.
(ii) Rectification
90 Mr Neil considered that underpinning was required where the cracking was the most severe at the western end of the dwellings in the garages, during the conclave he amended this to agree with the recommendations of Mr P. Haworth set out below. He also considered that given the amount and nature of cracking and the defects in the balconies on the first floor that the front façade needed to be rebuilt.
91 Mr Haworth considered that the whole house had to be underpinned as the soil classification of 'H' means the founding soil is a highly reactive clay which can experience high ground movement from moisture changes. Further, rock had been found in a number of bore holes. This meant there were footings founded in clay and which could move up and down substantially under changing soil moisture and footings on rock, which could not move. This was further exacerbated by the mixture of articulated masonry veneer and articulated full masonry which means the masonry has different degrees of stiffness which will result in substantially different cracking patterns and amounts of movement for the same soil moisture change. He considered if you were to partially underpin you would have to fragment the building works into areas isolating one area from another. He considered there was too great a risk of differential settlement with partial underpinning.
92 In the engineer's discussions Mr P. Haworth and Mr R. Neil agreed that the rectification would require full underpinning and Mr Neil recommended the underpins be set at a maximum depth of 3m, preferably on rock. Later in the conclave, upon further consideration of the rectification works required, it was realised that if full underpinning took place the additional footing beams for the re-entrant corners would not be required as the whole building should be founded at or near rock. Mr Brown agrees with the other engineers that the footings at and adjacent to the façade need to be rectified to ensure they have sufficient strength. He would recommend that they removed and replaced. He does not consider that underpinning will be of assistance as he considers that the primary soil movement mechanism driven by a changing soil moisture regime is heave and not settlement.
93 Mr R. Brown agreed with Mr R. Neill's contention that given the amount of movement and the lack of tie beams to the re-entrant corners of the entrance they should be underpinned.
(iii) Footing Design
94 In relation to the engineering design, under the 96 standard, Mr Howarth considered that it was under designed. The structural engineer, Mr Brotchie, had designed the size of the footing upon the basis that as it was a mixed construction between articulated full masonry and articulated masonry veneer and as such under Table 3.6 of the 96 Standard, where the external walls are articulated full masonry and the internal walls are framed the 'equivalent construction' under the table is masonry veneer and the footing system can be 'designed as if the construction was masonry veneer'. Mr P. Haworth did not consider that this was a valid assumption in this case, especially with the party wall which had to resist the torsion from the settlement of the dwellings either side of it. He considered that it should have been designed as articulated full masonry with a minimum depth of concrete in the footing of 1100mm as per the table in Fig 3.6 'Strip Footing Systems' of the 96 Standard.
95 Mr R. Brown considered that the full masonry party wall which has plasterboard upon it would qualify as masonry veneer and he considered the engineering design using equivalent construction satisfactory.
96 Mr R. Neil agreed that the engineer could have used the equivalent construction of articulated masonry veneer under the 96 Standard. Mr P. Haworth disagreed for the reason that as one of the major thrusts of the 96 Standard in its changes from the 88 Standard was that the depths of beams needed to be increased to improve the performance of dwellings and he considered that 1100mm depth for articulated full masonry was necessary. Mr P. Haworth considered that if the engineer was going to use equivalent construction and a shallower footing beam depth then he should have explained this on his Form 13, this is so the other building professionals would be aware of his design assumptions.
97 Mr Bolwell disagreed that merely placing plasterboard on full masonry would make it equivalent of brick veneer and thereby masonry veneer. Mr R. Brown agreed with R. Neil that although they were separate dwellings the party wall meant that they should be treated as a composite. Mr Brown doesn't have the same degree of concern about torsion and twisting of the footing beams as does Mr R. Neil and Mr P. Haworth. Although he agrees with Mr P. Haworth that the footing beam to the party wall is too weak to resist torsion at the western end of the dwellings due to the front façade being offset at the party wall by 900mm. Mr P. Haworth was of the opinion that if the building was to be treated as a composite it needed to have continuous beams, so that the offset beams at the front are strengthened by a cross-beam across the full front of the dwellings along the alignment of the footing beams of the more rearward dwelling, Mr W. Bolwell agreed.
98 Mr R. Brown considered the footing beams should have been continuous across to the party wall for the re-entrant footing beams from the outrigger entrances as in their present construction they had no strength to resist differential settlement. Mr Brown didn't disagree with the engineer's footing design but he did consider that the 96 Standard required plastic sheeting on the sides of the footing. Mr Haworth and Mr Neil agree that the strip footings of the outrigger entrances need to be carried across to the party wall to provide this torsional stiffness to resist the rotation of the entrances. This would not be necessary provided the rectification was full underpinning.
(c) Masonry Control Joints: Design and Construction
99 Mr Neil do not consider that a mere reference to the Masonry Code in the architectural drawings was sufficient to detail the masonry control joints and he considered their location should be depicted on the architectural elevations to ensure there are sufficient number and at the correct spacing.
100 Mr Haworth considered that some architectural plans showed the location of joints and some don't, whether they are shown depends on the terms of the contract between the builder and architectural draftsman and whether the builder wants to select the location of the joint. He considered that the specification sufficiently detailed the required locations of the masonry control joints. Mr Haworth agreed the location of the joints was not normally shown on the structural engineering drawings. He considered that the masonry controls joints should be designed so as to provide proper articulation and operate correctly in the circumstances the proposed building is likely to face. He considered this was mainly a construction problem in this case.
101 Mr Bolwell offered no criticism of the failure to depict masonry control joints on the architectural plans. Although, he considered the joint spacing specified on the structural engineering plans of 6m to be too wide for rendered full masonry and it should have been 5.5m maximum.
102 Mr Brown considered that the specification and plans described the location of the masonry control joints sufficiently and there was sufficient detailing on the architectural plans in the notes referring to the Masonry Code at Sheet 6 of the Working Drawings. Mr Brown agrees that the masonry control joints have been badly constructed.
103 Mr Neil and Mr Haworth concurred that the failure of the footings was the most substantial defect leading to the severe cracking of the buildings and not the incorrect location and construction of masonry control joints.
(d) Termites
104 Mr Haworth noted that the builder had left the gap in the footing wall of the party wall that allowed the termites to go from one property to another and he also considered it would be a defect under the regulations to prevent the spread of fire between dwellings.
(e) Building Surveyor
105 In relation to the building surveyor, Mr Haworth, considered that he or the building inspector should have picked up the lack of depth of concrete at the footing inspection and also check that the bearing capacity of the soil was not less than 150kpa. Further, the building surveyor should not just accept a Form 13 from the engineer but should check to see that it is correct and he can place confidence in the certificate.
106 Mr Bolwell considered that the building surveyor should not have accepted his soil report from the previous year unless he did so in writing, as per the Building Commission's letter of 16 August 2004. Further, the building surveyor could not use the soil report as the use of strip footings on articulated full masonry construction was not allowed under the 88 Standard and only piles or pier and beam could be used to support full masonry.
107 In relation to the Form 13, Mr Brown considered that the building surveyor has to accept it in accordance with the recommendations of the Building Commission. Mr Brown considered that a new soil report would have been desirable but that the soil report was mentioned on the engineer's Form 13 and therefore, it was the engineer's responsibility for accepting the soil report and not the building surveyor's.
7. ARCHITECT'S CONCLAVE
(a) General
108 The architect's conclave to consider the allegations against the architectural draftsman was attended by Mr D. Gairns, building consultant for the owners; Mr P. McLaughlan, architect for the owners and Mr B. Miller, architect for the architectural draftsman. The participants considered that there were four issues they should address;