Structural & Civil Engineering in Guernsey since 1990

D & B or Design & Dump?

  • D & B or Design & Dump?
  • D & B or Design & Dump?
  • D & B or Design & Dump?

October 2011

Design & Build or Design & Dump?

'Design and Build' (D&B) is not a method of construction. It is a method of procuring a building that represents a different way of managing some of the risks associated with the traditional form of procurement - where the risks associated with the interface between design and construction are normally retained and managed by the client.

D&B is increasingly popular with clients as the risk primarily lies with the contractor and the process is relatively easy to understand. With D&B, the project is specified to be designed (at least in part) and built by the same contractor, which in theory allows for greater collaboration and co-operation.
However, the route to any successful construction project still relies heavily on the three Cs - Communication   Communication   Communication.

The information provided to the contractor at the inception of the design phase is critical to the success of the project. D&B provides the client with a building that meets their performance criteria to a standard that they wish to see, and within a set budget and timescale.

By placing the risk of the design and build on to the contractor, it does not necessarily follow that the client will achieve the cheapest of build costs. D&B is more suited to experienced developers and clients, those who have a good understanding of their final requirements early on in the process, or for projects of a more complex nature.

Incorporating the design and build teams together at an early stage brings many benefits in the construction process. Engineers and architects (the designers) have many ways in which to develop a design solution and, with the addition of the contractor early in the process, they are able to verify the design to match the buildability, cost and programme requirements.

The major building risks associated with any post-planning project are usually below ground level.
You cannot be certain of what you cannot see. Within areas of the Channel Islands, there is a recurring challenge when undertaking both commercial and residential developments, where a combination of soft ground and a high water table is potentially a high risk to a project.

This is especially relevant when underground structures are incorporated within the building footprint to provide car parking or habitable spaces, such as a gymnasium or cinema. These features are becoming much more common in the Channel Islands, where pressures to maximise return on land costs is paramount.

At the T&G Group, we believe that the skill of the engineer is to mitigate risk whilst trying to minimise the use of raw materials and thereby reduce cost.

A recent project worked on by Jonathan Moffett – a Director of the T&G Group - looked at ways of founding a housing development on difficult ground conditions. A perched water table level and soft ground to a depth of five metres precluded the use of trench fill foundations and pointed towards the use of a more traditional pile and ground beam solution. Accordingly, a scheme was produced for financial appraisal.

As an alternative, Johnny approached the piling contractor with a view to exploring the possibility of using their soil mix technology, which had been developed specifically for cut off walls – his idea being that the cement grout be mixed in situ with the sub-grade material to achieve a suitable safe bearing pressure for the individual dwelling units.

Following field trials and a rigorous assessment of the soils, this proposed solution was successfully adopted and, in addition to the time saved, generated a cost saving on the foundation elements of approximately £2,000 on each of the 35 units – more than covering the cost of the Engineer's fees!.

Similar cost, time and environmental advantages can be realised through the application of sustainable urban drainage systems (SuDS) or SuDS-type systems.

The T&G Group is securing strategic partnerships and developing new professional relationships in order to bring best value to its clients. With links to the world-renowned expert in the field of pavement systems, Dr John Knapton, we have used permeable hardstanding on a number of recent projects to provide for the removal of surface water in areas where traditional tarmac and piped drainage solutions were considered impractical.

Jersey, Guernsey and the other islands are fast following the UK, where there is a growing acceptance that we need to have a more sustainable approach to managing surface water. SuDS mimic natural drainage processes to reduce the effect on the quality and quantity of runoff from developments whilst also providing community and environmental benefits. For example, sustainable drainage can be integrated into strategies for public open space and green infrastructure within developments while the resultant improvements in the visual attractiveness of a development have been shown to increase its value by between ten and 20 per cent. However, it should be stressed that when specifying SuDS, early consideration of potential benefits and opportunities will help deliver the best results. 

If you would like more information about the benefits afforded by these alternative solutions or would like to know more about our knowledge and experience in the field of D&B, please contact Ian Bashforth on 01481 714344 or e-mail us at admin@malgsy.com

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