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Absolutely prefab

Rob Ackerman, technical manager of Speller Metcalfe Living Limited, looks at the pros and cons of prefabricated buildings

Posted by Dave Higgitt | December 29, 2014 | Bricks & mortar

The use of prefabricated buildings, otherwise known as permanent modular construction (PMC), is considered a controversial topic within the construction industry. There are divided opinions over whether construction professionals are neglecting clients with an off-the-shelf product that lacks architectural floridity or are instead offering a quick and efficient delivery method. It should also be considered that the local economy may suffer from PMC undercutting local supply chains and sub-contractors. 

Permanent modular construction is an offsite-based construction method whereby several components are manufactured off site and then finally assembled on site to reach project completion. This method offers an alternative approach to traditional construction as manufacturing is prioritised - with the planning and design stage playing a fundamental role in the overall success of the project. 

There are many pros and cons to the use of pre-fabricated buildings and for this reason clients must consider PMC on a project-by-project basis. For instance, if a client has a project brief which consists of a repetitive building design it would appear logical to use a technique which creates a set of standardised components that can be designed into a single, repeatable product - saving time and money as a result.

Below are factors to be considered when deciding between PMC and traditional construction: 

Pros

  1. On site construction time is shortened considerably.
  2. Many health and safety risks can be reduced or eliminated through working in a safer factory environment.
  3. PMC is a form of lean construction - an approach which aims to maximise value and minimise waste. PMC produces less waste as materials are pre-measured, scheduled and fabricated at works.
  4. A project’s carbon footprint should be considerably less as fewer people are travelling to site.
  5. PMC ensures robust construction methods which can assist in the airtightness of the building, beneficial to energy efficiency and to achieving Passivhaus standards.
  6. PMC benefits the current skills shortage, with between 60-90% of work being manufactured off site in controlled environments.
  7. All fitted specialist components are factory quality controlled and have full mechanical and engineering equipment already in place before being installed on site.
  8. Safety systems are incorporated into each component, e.g. steel systems with pre-welded roof edge protection or safe tether points for fall restraint systems.
  9. Impact on the community during construction can be significantly reduced in terms of noise, traffic and period of work on site.
  10. Certainty of timescales for the delivery of projects is maximised through the allocation of manufacturing, fabrication and delivery slots.
  11. Developments in Building Information Modelling (BIM) has minimised the risk of design errors during the manufacturing process. BIM allows for a design to be properly tested for clashes and clearance zones, as well as the construction sequence before manufacturing.
  12. Using CAM (Computer Aided Manufacturing); components can be repeatedly cut into their exact digital representation. The accuracy at design stage often allows for a design to be more tolerant than current industry standards. 

Cons

  1. Traditional construction allows for later design changes (on site if necessary) but with pre-fabricated buildings this is near impossible. As a result, early sign-off of final designs can be made an unnerving experience for clients.
  2. PMC can take away a project’s architectural flair as pre-fabricated buildings are often considered an off-the-shelf product.
  3. The suitability of sites for PMC must be fully considered at the outset in terms of access for the delivery of large modules and provision of adequate lifting equipment.
  4. Opportunities for a localism approach to construction can be decreased as PMC eliminates the need for local suppliers and sub-contractors.
  5. PMC can make the liaison stage of the project even more intense, as the components arriving on site are large and the logistics and planning to erect these components can be disruptive to the general public.  www.spellermetcalfe.com/living

 

 

 

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