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Case Study: St. Clair Park Village Floor Truss Project
The development of St Clair Park village to the west of Auckland comprises 110 individual three story timber framed units, generally in blocks of four and five.
The timeline for the project was for a start date in January 08 and completion in August 09.
The designer specified solid timber joists using MSG10 material, often spanning 5590mm
The project builders had an expectation from previous project experience that the framework from slab to roof for a five unit block would take approximately 5 weeks:
• Week 1: ground floor wall frames and first floor joists
• Week 2 and 3: second floor wall frames, second floor joists, third floor wall frames
• Week 4: truss erection and installation
• Framework and associated nogs, battens and fixings completed within five weeks.
Upon becoming aware of difficulties in sourcing long lengths of 290x45 MSG10, the fabricator for the roof trusses and wall frames identified an opportunity to supply a floor truss system.
The fabricator prepared easy-to-read documentation and constructed a full scale model on the factory floor to demonstrate the simplicity of construction.
The benefits of the Pryda Span floor truss system was as follows:
• Manufactured to exact lengths with end configurations to match support requirements exactly - eliminates on-site cutting time and waste
• Plumbing, ducts and electrical wiring easily installed
• Lighter than solid timber but stiffer and less prone to damage than other engineered systems. It is far easier to lift a Pryda Span into place compared to a 12x2 inch floor beam.
• Delivered in packs to site, marked in logical order along clever prefabrication of boundary joists – removed the need for coordination by the builder or reliance on accessing specific building materials
There was an increase in material cost for the floor of around 6% when using the floor trusses instead of 290x45 MSG10 solid joists.
Despite this the builder could see the cost benefit for the entire project.
The project became a major success with the floor truss system providing the following benefits:
• The 5 week building time for floor to roof framing reduced by almost 2 weeks (up to 40%)
• A direct labour saving associated with a gang of 6 labourers, providing a direct cost benefit that was 2.5 times larger than the material cost increase.
• Tradesmen found it easier to carry out their jobs due to the user-friendly nature of the Pryda Span floor trusses. (Plumbers and electricians in particular)
• The critical path of the building time for each block of units by around 15% (2 weeks/17 weeks)
• The builder was in a far better position to meet the August deadline and therefore minimised the chances of project overruns and the associated indirect costs
In this case the consent documentation was not amended prior to changing floor systems, so Waitakere CC was very helpful in reviewing and accepting changes during the construction process.
Pryda’s engineers were quick to assist and provide the council with confidence in the structural integrity of the floor truss system. They even conducted a special training program for the council so that inspectors were more familiar with what to look out for on site.
On face value the comparison of cost per lineal metre of joist did not reveal the underlying cost benefit of using floor truss systems.
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