Property Development

The Art Of Preserving Our Heritage Buildings

NWE Consulting Engineers
By Madeleine Visagie

The tricky truth to how NWE preserved the Jazz Workshop Building when designing the new City Depot on the corner of Buitengracht Street and Hout Street, Cape Town.


Some buildings epitomizes the whole character of an area, and if this is not protected, we stand the risk of losing some valuable elements of our heritage. This is also the case with the Jazz Workshop Building on Buitengraght Street. However, when the City of Cape Town: Electricity Services appointed NWE Consulting Engineers and EBESA Architects to design a City Depot on the site, it took a great deal more than good intentions to preserve this small part of our heritage.


Heritage Aspects:

The original structure of the Jazz Workshop Building dates back to the 18th century, if not earlier, but it underwent a substantial makeover apparently in the 1950’s. Notwithstanding the makeover, the building retained its overall early form including general front fenestration pattern and proportions.

Figure 1: The Jazz Workshop building is situated on Buitengracht Street at the corner with Hout Street.


Since the demolition of the structures surrounding it, it has become a local landmark on Buitengracht Street despite its modest size. Since 1965, the building has become strongly associated with jazz education and jazz performance in Cape Town. It is clearly significant by virtue of its strong historical associations with the development of jazz in the Mother City, particularly during the time of apartheid. The building also contains early surviving brickwork dating back 200 years and possibly more.

The Jazz Workshop building makeover is now older than 60 years and the whole building has predominantly contextual rather than intrinsic architectural / aesthetic and historical significance. It was graded therefore by ARCON heritage consultants as a historic building contributing significance. By retaining the front part of the structure it would enable the majority of the ancient brickwork surviving as well as the period joinery (staircase and doors) that survived with in the building.


Structural Challenges:

The architectural design of the City Depot incorporated a basement covering the whole site. The design and construction of the basement had to take in to account the protrusion of the founding material of the Jazz Workshop building.

Another challenge N W E’s structural engineers had to take into consideration was the nature of the original foundations of the historic building. It was alleged to be stones bonded with products not containing any cement. If construction activities caused ground movement due to the excavations of the new basement, vibration from drilling, hammering and blasting, the brittle founding material could cause cracking or maybe failure of the historic structure.

It was decided that the courtyard and backroom adjacent to the stair should be demolished. This has the result of a simpler, compact and symmetrical building and could be “strapped” around the perimeter.


Figure 2: Ground beam cast around the existing founding members of building to counter possible cracks in the   building or failure of the building during the installment of the piling wall for the basement.



N W E and the contractor Group Five had to come up with a construction methodology that would ensure the historic building remained intact. The following actions were decided on and was executed with the utmost care.


  • The suspended timber floors in the Jazz Workshop Building were propped from groundfloor up.
  • Tie bars on the outside of the building were installed on each floor level. They were tensioned and grouted.
  • The backroom was demolished with caution by using mechanical breakers with a low level of vibration.
  • Tempory bracing rods were installed and tensioned on the outside walls to increase stability of the structure.


Figure 3: Temporary bracing and lateral stabilization of the founding material underneath the heritage structure.


Another problem always encountered when dealing with historic buildings is that failures of these structures happen when the bottom parts of the walls kick out to the sides. Therefore the next step was to contain the founding members of the walls at the bottom to ensure the building do not collapse when piling and excavations for the basement commence.

A ground beam 450 mm wide was cast right up against the existing walls and foundations on three sides of the building to stabilize and secure the foundations and walls (See Figure 2). With these ground beams cast and cured to the specified strength, piling around the Jazz Workshop building could commence, considerably reducing the risk of the foundations collapsing.

All went well up to this point, but as perceived existing cracks started to form at the back corners of the historic building. Erik van Eeden, our structural engineer on site, instructed the contractor to contain and close these cracks by using 100 x 6 mm plate straps 4m long around the corners. (See Figure 3).

The piling and lateral support for the basement were designed and supplied by Franki Africa. A 300 mm diameter DTH (down the hole) pile wall (piles at 1200 mm c/c) was created around the perimeter on three sides of the Jazz Workshop Building.

In DTH (down the hole) drilling, the drill string rotates while the drilling hammer continuously strikes down into the founding material. The method was chosen because it produces significantly less vibration than many other drilling methods, making it the safest drilling method in the vicinity of the heritage building.

A triumph! The installation of the 26 piles around the Jazz Workshop did not cause any more cracks or further problems in the building. With the piles in place and the historic building still intact, a capping beam was cast on top of the piles. At that point the existing foundation of the building could be considered as underpinned and the excavation and lateral stabilization of the basement could commence.

Lateral stabilization of the founding material underneath the heritage structure for the basement excavation was created with a gunite wall and 25 mm permanent dead man anchors. (See Figure 3.)

No extra precautionary measures for the stabilization of the building were taken during the excavation of the basement material and the construction of the gunite wall.

The construction of the new six level concrete building continued without any further challenges to the preservation of the Jazz Workshop Building.

In the end, despite the structural engineering and construction challenges, the Jazz Workshop Building was preserved for generations to come and it still stands proud and snugly embedded into the modern era.


Figure 4: Construction nearly finished around the Jazz Workshop Building

Pro Pac 5 Is Here

NWE Consulting Engineers

Manage your risk and reap the rewards, with the help of NWE’s latest release of their in-house project feasibility program.


In a nutshell, what is Pro Pac 5?

Pro PAC is an acronym for Project Performance Analysis Calculator and we use it to determine the viability of any given property development project.  Pro PAC 5 is the latest release of the program that had the first version developed in 2005.  Pro PAC models the entire life cycle performance and cost of a property development project, from inception and technical viability through completion and financial viability.


Why have you decided to develop your own software for NWE, rather than using excel or other tools like other development companies?

Most developers and financing institutions use some form of software, past experience and “gut feel” to undertake due diligence studies or analyse the viability of development projects.  More often than not these solutions are spreadsheet based applications, spreadsheet add-ins, and time management software such as MS Project or Primavera and in certain instances even some form of business management software.

While something similar to Pro PAC may well exist, we have not come across anything that is as comprehensively tailored for analysing property development projects.

The “problem” with most spreadsheets is that they are often written for a specific set of circumstances and as soon as the parameters change (as is inevitable with property development project viabilities), the need arises to amend or update the spreadsheet to fit a new set of circumstances or different needs expressed by the client.  This creates the very real possibility of introducing errors into the spreadsheet which obviously compromises the accuracy – not something you need when important financial decisions are based on the output.  Even with care and testing the re-writing of spreadsheets remains a tedious if not laborious process.

Pro PAC has been designed and developed as a powerful application that is robust, but with sufficient built-in flexibility and options available to enable the user to model virtually any scenario that may be reasonably expected.


For how long have you been using the program and how have you been testing the accuracy of its results?

We’ve been using the application since 2005 when Pro PAC 2.0 was launched.  This version was really the start of the new generation analysis software – no more fiddling under the bonnet so to speak. The original tool on which Pro PAC is based was a simple spreadsheet circa the 1990’s used by our CEO, who although being a civil engineer by trade, is also a property developer in his own right.  Being both engineer and developer, Wouter also understands the procedural and commercial complexities of property development, not merely the technical and financial issues associated with a particular built environment discipline like most consultants do.

Over the past 17 years we’ve had the opportunity to assist many clients with their development projects using this software and overall the modelled outcomes consistently showed good correlation with reality at the end of the projects.  As always however, no software, regardless of complexity and accuracy, is the magical answer to all questions.  The software is merely a tool and outputs are only as reliable as the inputs.  This is why it is essential for the user to be intimately familiar with the subject matter he is advising the client on – in this case property development analysis.


What are the most important questions project owners want to answer when using the new Pro Pac 5?

Basically everybody needs to know if a project is going to yield an acceptable rate of return on their investment, what the profits are likely to be and when the profits will realise.  We however understand that while certain types of information remain important regardless of the project stage, the need for other specific information changes with time.  The whole idea is to empower the client to make informed decisions, based on reliable information throughout the entire life cycle of the project.

Pro PAC does all of this and more.

For example, when clients are in the process of evaluating a potential land purchase, they would like to know whether the asking price will fit in with acceptable returns for the project.  Depending on the complexity and make-up of the proposed development, we can create a working viability model within two hours of consultation with sufficient accuracy to provide the clients with enough substantive information to undertake their land purchase negotiations or to make the decision to investigate other properties.  In this manner much time is saved (for the client and the consultant) by not wasting it on fruitless negotiations and investigations, or confirmation is given at a very early stage that it is worthwhile pursuing and concluding a deal on the land.  All this without any need for input from other built environment professionals.

During the viability and design stages of a project when town planning and engineering layouts become available and more accurately estimated costs (construction, fees, sales income, levies, taxes, interest etc) and timeframes are available, the model is refined and calibrated putting us in a position to accurately identify areas of time and cost risk, where to focus effort to manage these risks, as well as calculate project profit and rates of return on investment.  Rigorous sensitivity and risk analysis plays an important part of the analysis.  All these outputs are obtained instantaneously as the input parameters are updated and tweaked.


What is new with version 5?

While Version 5 remains true to its roots, it is a total re-write from the ground up.  Some of the enhancements and new features include:

  • An entirely new user interface, now with windows ribbon controls instead of the older style toolbars.
  • A new project file management system.
  • Some updated algorithms for increased efficiency.
  • There is a new “Key Point Indicator Dashboard” that visually summarises all important outputs such as return on investment, project profit, comparison between the individual profitability of various erf or unit types on offer etc.
  • One of the most important upgrades is in the Gantt Chart functionality.  While previous versions also used the project programme as the backbone of everything, Pro PAC 5 now enables time programming with task linkage functionality.  Tasks are therefore now automatically scheduled or updated dynamically as inter-dependencies come into play and allowing for critical path analysis for instance – something Pro PAC couldn’t do before.


How does your clients get access to Pro Pac 5

Pro PAC is not a commercial software package, nor is it for sale.  Pro PAC is one of our most important marketing tools and we provide this service and the added benefit derived from it to all our property development clients – free of charge.

Whether Pro PAC is your way for checking your own analysis results, or whether you rely on it exclusively to base your development decisions on, we invite you to visit us and to experience the power of this unique tool first-hand.

Get in touch with Michael Smuts at or Wouter Engelbrecht at


What does the future hold for Pro Pac? And is there any other programs that you would still like to develop for NWE?

The new time programming functionality opens a whole new range of possibilities as far as time and risk management is concerned.  I am already working on additional routines to perform Monte Carlo analyses which will:

  • Allow the running of thousands of iterations using refined randomised inputs, recording and then analysing results statistically.  This enables us to add a statistical certainty level to our output.
  • Determine which tasks are driving the time sensitivity of the programme (potentially entering or leaving the critical path and how frequently this happens, ie influencing the end date)
  • Countering the phenomenon referred to as “merge bias” which basically states that all time based programmes are essentially (if unconsciously) optimistic.


Hopefully this functionality will become a permanent feature of Pro PAC within the next couple of weeks.