This article introduces, through examples, causes of the high cost of fixing defects in recently constructed residential strata buildings.
What are the main drivers?
While not all the causes of defects can be discussed here, major contributors to the Cost of remedial works include:
- builder/developer rush to completion
- design and construct simplifications, detailing for constructability, not durability
- inadequate oversight during the works
- code limitations
What are some typical defects?
Some common defects that impact the building structure are covered further below. At the time of construction, such defects can be dealt with cheaply and quickly. However, due to site pressures and inadequate oversight, good detailing is often glossed over.
This is a review of common examples, taken from recent projects: sliding door termination height, wet area thresholds, and unbuildable code details.
Sliding door termination height
Step-downs in slabs complicates the formwork and so increases time and cost of construction, and in some minds, clutters the aesthetic by having different levels between inside and out. A few decades ago, there was a trend to minimising or eliminating the step down at sliding door thresholds, while eliminating the hob.
Of course, water ingress is the result. Since 2009, to address this, the threshold termination height has been defined in AS4654.2 Waterproofing membranes for external above-ground use and yet structures still get built without the required termination height.
The photo below is taken from a detail simplified by design. While partially protected by a deep overhang, a maintenance-spray of water resulted in leaking where the hob and termination angle had been omitted. However, the design at the sliding door threshold did not comply due to the finished tile levels being flush with the floor, whereas at least a 70mm termination height should have been provided.
Figure 1 Sliding door detail simplified – threshold termination height reduced/omitted
What are the costs? For a 4.2m sliding door where a hob or suitable termination angle were omitted, it would take additional coordination, materials and labour to install a suitable termination angle and extend the deck membrane onto it. Let’s say it a 5m length of angle, and an additional 2L of membrane, plus ½ day of labour. This might cost an additional $350-450.
However, remediating the issue after occupancy entails: establish access, remove sliding door, remove tiles and membrane, prepare and prime, install termination angle, clean, prime, re-membrane and tile, cure, install new sliding doors, make good perimeter of opening. render, cure, paint, then demobilise. For a 24sqm balcony, these steps over several days’ could easily cost $15-18,000 – up to 40 times the cost of getting it right first time!
Wet area details
AS 3740 Waterproofing of domestic wet areas sets out requirements for wet areas. Issues often encountered are poor detailing of thresholds, around door jambs and corner joints.
A recent example of poor workmanship with a tile threshold angle arose from poor coordination of falls and resulted in duplication of the tile angle. To avoid this would have taken a little more communication, and purchase of a larger angle. For a 900mm door opening, this may add $50 to the job.
What are the costs? Replacement of the badly installed angle entails the demolition of tiles with unacceptable risk of damaging the membrane, so remediation extends to re-doing entire bathroom to maintain warranty. For a modest bathroom, re-doing membrane, tiles and door thresholds costs in the order of $12-15,000 …300 times the cost of getting it right up-front!
Figure 2 Duplicated threshold angle, separated and corroded jambs
Unbuildable code details
AS3740 Waterproofing of domestic wet areas sets out details for waterproofing bathrooms and the like. It covers a lot, and has evolved since first issue in 1989, however still contain inconsistencies that could mislead the inexperienced. It is a referenced standard in the BCA, meaning it must be complied with.
However, Figure 3 below shows a detail that cannot be built without modification. One issue is that the dashed line representing the membrane is shown passing under the hob material, and implies that the bend between the floor and upstand sections is simply “painted on”. If this approach is attempted, the internal corner of the membrane is prone to fail due to pinholing, thinning, or low movement capacity.
Figure 3 Extract of AS3740 Figure 3.12 “TYPICAL HOB CONSTRUCTION”
To avoid this issue, the membrane should be placed, with fillets, after the hob and to fully encapsulate it, as shown by the blue dashed line. This route would also be warrantable by the contractor.
What are the costs? To add the fillets and run the membrane over the hob, then extend the membrane across the floor would involve additional material and labour. Material and labour would be modest for an average bathroom, but let’s say $100 for materials and $250 for labour.
Fixing a failed hob membrane after cracking at the base of the hob after occupancy would involve the same full-bathroom repairs as for the previous example. Some $12-15,000 …some 60 times the cost of getting it right up-front.
In summary, the cost of remedial works is largely impacted by the additional coordination, protection and access requirements arising from working in an occupied building.
Additional costs are incurred when the remedial works have to be warranted and insurance provided. Below we summarise the relative cost of examples given:
|Defect||Original Cost||Remedial Cost||Multiple|
|Sliding door threshold||$450||$18,000||40|
|Wet area threshold||$50||$15,000||300|
|Unbuildable shower hob detail||$250||$15,000||60|
Clearly, the penalties for getting simple things wrong at the time of construction are inordinately high.
ACRA encourage interested parties to examine the materials available on our website www.acrassoc.com.au and consider signing up for the new course or to find details of ACRA members that can assist with diagnostic or remedial works on your structure.