Preliminary and developed designs

Preliminary design

Preliminary design is the development of options for remediation and and improvements that can be discussed with the owner and builder. A quantity surveyor may be engaged to provide initial indicative costings of the options being considered.

For remediation projects, basic design parameters of orientation, form and layout are pre-existing. 

Preliminary sketch designs may be rough and exploratory as the first translation of requirements into graphic forms. However, they should still allow the assumptions used in the earlier preliminary estimates to be checked and take account of the preferred design solution and its detailing. 

At the start of the preliminary design, the designer should fully understand the weathertightness defects and the extent of moisture penetration and deterioration to:

  • address the nature and extent of the failures 
  • assign priorities to repairs 
  • explain the extent of the damage that needs to be included in the repair
  • mitigate the risk of future problems
  • define the extent of improvements that are desired and/or can be accommodated within the owner’s budget
  • explore with the owner what the repaired building can look like with different concept options
  • provide initial cost estimates, including contingencies, by a quantity surveyor of options available based on the preliminary design, ensuring that this is not a double-up on what was done for the building condition and remediation report. 

Areas that are difficult to detail should be considered early. The design process should either simplify or remove difficulties and solve them with initial sketches of critical details rather than leave them until later when a solution may be significantly harder or impossible to achieve without major or costly rework. Known high-risk features and areas of difficulty should be focused on and detailed clearly.

There should be a thorough design audit at the planning stage to ensure that sound weathertightness design principles are being followed.

It may also be advantageous to discuss proposed design solutions with the BCA to ensure potential conflicts are sorted early rather than having the BCA reject a consent application because they are not satisfied that the solution will be Code compliant.

Most repair details need to be designed to suit the specific circumstances of the building, but the principles of E2/AS1 should still be followed. It is wrong to follow a detail that was used in the original construction when a lack of performance has been demonstrated.

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Developed design

Developed design is where design options, material choices and degree of improvements are finalised with the owner. 

To enable estimated costs to be firmed up, the final design should address:

  • the agreed extent of work, including improvements
  • prioritisation of the work – staging work can increase the overall cost of the repair because of the additional set-up costs for each of the stages
  • selection and detailing of materials and finishes to make sure the concept will work
  • difficult-to-detail areas of the project.

Developed design should also take account of:

  • future maintenance requirements (and the ease of carrying out that maintenance)
  • published literature on building practices, for example, BRANZ Good Practice Guides
  • manufacturers’ literature
  • product appraisals from organisations such as BRANZ and the conditions of use for the appraised products 
  • BCA requirements – discussions with the BCA may be required where there are specific consent requirements that may need to be resolved, any quality assurance requirements, Code compliance or other issues relevant to the project and to establish the level of BCA inspections that will be needed during construction.

Updated: 17 September 2017