Housing affordability – concrete delivers

Concrete is improving housing affordability in Australian metropolitan areas. As land prices in urban areas continue to push the Australian dream of home ownership further from the reach of first time home owners concrete is reducing the unit building cost of homes through innovative construction methods.

For a developer of new homes the challenge of containing rising land prices can be managed by improving the home to land ratio to produce a more affordable home. Using an innovative method of concrete construction an architect was able to design six townhouses, each with off-street undercover parking, to fit on a single average sized suburban block. 


The land site is located in the Brisbane suburb of Nundah and measures 15.5 metres by 40.5 metres which at 628 square metres was previously occupied by a single dwelling. Using innovative concrete walling the six townhouses were able to be designed to fit comfortably next to each other completely within the land boundaries. This was able to be achieved by using concrete as the walling solution.


The designer selected an in situ concrete walling system utilising permanent formwork which has the remarkable ability to produce thin wall sections which satisfy the building regulations for common party walls between adjoined dwellings. At a thickness of only 165 mm the concrete walls satisfy the requirements for both fire and noise, making it an ideal choice in this application. Through the ability to produce thin strong and safe walls concrete was the prime reason that made this development successful.

The walls were constructed using the Ritek permanent formwork system which is a prefabricated formwork consisting of two separated and parallel fibre cement sheets. The fibre cement sheets form a hollow void into which horizontal and vertical steel reinforcement is placed and then filled with liquid concrete. This creates a wall with the strength, robustness and integrity of solid reinforced concrete.

The fibre cement sheets permanently remain in place as the outer surface of the wall. They can be rendered for an outside finish and for an inside finish the joints are set plastered and the wall painted. The sheets, in their original assembly, are separated and sturdily held in position by non-ferrous patented studs. Each of the two fibre sheets is 6 mm thick and together they enclose, for this project, a reinforced concrete core of 153 mm thickness giving a total wall thickness of 165 mm. At this thickness reinforced concrete is the only building material that can provide such a slender, strong and practical wall.

A big advantage to the builder of this walling system is the ease of construction. The pre-assembled wall panels weigh around 80 kilograms and with a team of three workers are easily moved and manoeuvred into position. With the steel reinforcement also manually placed into the forms the formwork erection is easily completed without the need for onsite cranage. Services are located within the walls by the use of conduits which are included prior to the pouring of the concrete.

The panels are temporarily braced in position and pump filled with concrete at a consistency of 200 mm slump. The high slump concrete ensures penetration of the concrete to all corners and nooks of the formwork to create a continuous solid concrete wall. The walling for one complete flooring level is normally poured in the one action and a flooring cycle for multi-level buildings of one floor per week is easily achieved.

Each townhouse consists of three levels with the ground floor being utilised for under cover car parking, the first floor for living and family rooms and the top floor for bedrooms. While concrete provided the winning solution for thin practical walls it also contributed in two other important building aspects to make the development work.

By positioning the six townhouses next to each other with the ground floor utilised for car parking and driveway access required the building to have long span first floor supports. This was elegantly provided by side shifting ground floor columns to the side land boundary and providing a cantilevered beam support for the first floor of the building. This created an intermediate column free ground floor area to facilitate safe car access and parking. This unique structural arrangement was provided by in situ cast reinforced concrete columns and beams. This efficient structural design could only be provided by a reinforced concrete solution demonstrating the value and versatility of the material.

The third area where concrete uniquely contributed to the success of the development was in the choice of reinforced concrete as the material for all of the floors of the project. This created structural continuity between floor, walls and overlying floor to produce a three dimensional structurally integrated continuously bound structure. This provides an inherently strong and stable frame for the building which is naturally secure and safe in extreme weather conditions.




Through three innovative and creative design and construction techniques concrete has contributed to reducing the building cost of this six townhouse development which is located on a small Brisbane suburban block. Keeping building costs low for residential housing is how the concrete industry contributes to increasing housing affordability in Australia. We believe that home ownership is more than just a dream.

Credentials:

Builder & Architect : Studio1

Permanent formwork system: Ritek