6 May 2011 – Bluescope Steel last night won the Insurance Council of Australia Resilience Award Competition with an innovative home design, by Caroline Pidcock of Pidcock Architects, aimed at preparing Australian communities for extreme weather conditions and assist disaster affected families to remain in their own homes post-disaster.
The design addressed five major weather events: hail, inundation, bushfire, extreme rainfall, and cyclone, in a sustainable context.
Ms Pidcock said Pidcock and Bluescope were able to work together to integrate durable materials into a very good design that understood the problems to be addressed and was inspired by this.
Prize for the winning entry was $50,000 from the general insurance industry.
Bluescope’s winning design was inspired by the recent Queensland floods, which affected many of the company’s customers and some of its staff.
The company took elements of its existing building products range (such as cladding, roofing) and incorporated well accepted design elements (from a market perspective) into a modern take on the “Queenslander” architecture.
Below is a summary of how the design’s “disaster resilience based on steel” home protects against extreme weather events and how the design allows occupants to remain within their homes post-disaster, thus alleviating costly accommodation costs and inconvenience
Hail (a sustained 20 minute hailstorm with hail up to eight cm in size and velocities of 125 km/hr).
A close pitched trapezoidal steel roofing product (BCA 2010 220.127.116.11) for the concept home because:
- It has a similar appearance to the corrugated profiles made from BlueScope Steel material, which is preferred by Australian home owners (corrugated profiles are typically referred to as a “corrugated tin roof” in the Australian vernacular) so is likely to have widespread residential market acceptance
- It has additional strength due to the shape of its ribs, which provide resistance to hail
- It has superior performance in extreme wind and rain conditions (see further details below); and
- It is readily sourced across Australia
In order to understand the issues associated with hailstorms and the performance of Bluescope’s roofing product in such conditions, it used “finite element analysis” to simulate the impact of eight centimetre diameter hail onto roofing sheets of varying thicknesses made from a close pitched trapezoidal profile.
Hail damage was simulated on both the lap section and the middle of the sheet. Using FEA they demonstrated that, in a hailstorm event, the 0.48 mm base metal thickness G550 material would suffer only aesthetic damage (via denting). Thus, tests indicate that any hail damage would be primarily cosmetic and the integrity of the roof would be maintained.
In addition, all of the home’s gutters have leaf guard to prevent hail from blocking the downpipes and to prevent overflow back into the building. The one metre roof overhang will further assist to protect the building envelope. Post-disaster, the composite ceiling panel will act as a secondary water seal (in the unlikely scenario that the roof has been structurally damaged).
Water Inundation (above the floor sill height of the property)
The composite steel and concrete panel used in the home’s walling provides a strong seal against water penetration into the interior of the ground floor. During a flood event, the occupants would place barricades (normally stored under the house) to seal openings on the ground floor (to be 600mm above the FFL). These barricades require the removal of a section of the doorframe before being simply bolted to the doorframe to provide a seal against rising water. As well as the barricades, occupants would also fit stoppers to the ground floor wall vent to further prevent the ingress of flood waters.
After the flood subsides, the barricades and stoppers would be easily removed, cleaned and stored until the next flood event. The ground floor of the building may require cleaning to remove any mud/dirt accumulated as part of the rising floor waters, but due to the sealing of the exterior, very little damage would be expected to the contents of the ground floor. Having most of the living areas on the second level means that the contents on these levels will be protected from the flood water levels prescribed in the criteria document.
Fire (exposure to external fire risks where radiant heat will exceed 40kW/square metres)
The home comprises a building composition (steel frame, steel roof, steel cladding) that has been shown to be flame-zone resistant in tests supported by the National Association of Steel Framed Housing and performed by the Rural Fire Service (using the Bushfire Flame Front Simulator) and CSIRO (see Attachment 3 and Image 1 below).
The BFFS facility is the only facility in the world that can model the immersion of a full scale structure in a high intensity bushfire flame front. Further, the walling materials of the lower floor of the concept home have been deemed to be fire resistant (as specified in AS 3600).
Ventilation to the roof space in the concept home is provided to relieve moisture from a well sealed roof cavity and to provide thermal comfort. In a fire event, this ventilation will be screened to prevent ember entry and vents will automatically close when air temperature at the vent exceeds 80oC. In accordance with BCA 2010 18.104.22.168B (adjustment for R value for 0.5 to 1 per cent roof area vents), four vents at 0.4 square metres each will be provided.
Gutters in the concept home will have leaf guard so fuel build-up is unlikely to occur and ignition via ember attack will be prevented. The one metre roof overhang would protect the building envelope even if there was fuel in the gutters and it was ignited by falling embers.
Shutters on windows or vents will be steel encapsulated fireboard or proprietary novel material and will protect window openings from heat and flames (addressing an area of weakness identified in the BFFS test) and the doors to the breeze-way would be closed for further protection.
The breezeway will be screened to prevent ember attack and all openings to the main living areas will be protected by fire-rated doors and/or shutters.
Therefore, based on the materials compliance, specific design elements and BFFS test in fire conditions, the home is expected to be resistant to external fire event and is likely to require only minimal repairs after the disaster event has passed.
Minor repairs might include repainting of the walls on the ground floor, repairs or replacement of heat affected shutters and doors and replacement of any heat affected roofing and walling components on the upper storey. It is expected that replacement of the home components will be required due to aesthetic, and not functional performance, reasons and in the case of the roofing and upper story walling materials due to aesthetic and durability issues associated with the exposure to the bushfire.
Finally, the home will incorporate novel use of water storage tanks in the building design, both to reduce the environmental footprint of the building as well as to provide a source of water to assist with fire fighting by emergency services. If all of the potable water is not required for fighting the fires, there is also the potential to have the water available for the building occupants post the fire event even if the mains supply is disrupted. This will assist the home occupants to stay in their home post disaster and put less pressure on damaged and potentially overloaded community infrastructure after the fire event.
For rainfall in excess of 50 average recurrence interval, or ARI, for one hour, excluding catchment flooding issues, the building is protected against immediate ingress of water falling on envelope. The proposed close pitched trapezoidal roofing profile has superior high rainfall performance.
The home design is based on a scenario of locating the building in Cairns, which gives a 20 ARI of 282 mm/hour and 100ARI of 368 mm/hr. Interpolating between these figures gives a 50 ARI of 315 mm/hr. Based on the information provided in an attachment, which should be typical for this roofing material, and without interpolating between data points, the maximum allowable roof sheet length for a 10o pitch is 43 m.
The concept home requirement is well below this limit, and the proposed roof pitch of 15o will further enhance the rainfall capacity of the roofing profile.
The designers chose downpipe and gutter selections to complement the roofing design while ensuring these met the Building Code of Australia rainfall capacity requirements. Based on 325 mm/hr rainfall intensity the deemed to comply specification is one 100 mm diameter round downpipes for every 40 square metre of roof catchment area (total roofing area of 240 sq m therefore eight downpipes are required – four per side). Gutter selection based on the same deemed to comply specification is 150 mm D section or similar with cross-sectional area of 7900 – 9000 sq m. To meet this specification, 175 mm half round gutter was selected.
Wind Gusts (exposure to winds in excess of 279 km/hr)
The concept home would be resilient to high wind gust. The close pitched trapezoidal profile was chosen due to its appearance being similar to the traditional “corrugated” profile but with greater extreme weather resistance, including wind gust. The designers used 0.48 BMT G550 material, fixed with cyclonic washers in accordance with the recommendations for a typical product (see Cyclonic Area Design Manual, Attachment 5).
The purlins are a minimum 1.5 mm BMT and spaced at 600 mm maximum. The extra thickness of the purlins (over what would be typically used in a non-cyclonic region) is to improve the screw pull out load capacity to take the larger forces generated in a cyclonic event.
Cyclonic washers (larger diameter washers) are used to help spread the load from the fasteners back into the roofing material, thus reducing the likelihood of the fasteners pulling through the sheeting.
To protect the most vulnerable part of the house (the glass windows) from wind borne debris, window shutters have been incorporated into the concept home design. It is expected that the shutters on all windows would be deployed before the storm event and that these would protect the glass as well as the interior of the building from damage.
Although not specified in the design criteria, it is also expected that the design of the house will also be able to withstand a reasonable impact from debris associated with a cyclone (as shown by the modelling of the hail impact). After the cyclonic event, the rectification would involve replacing any roofing and walling damaged by any impact of flying debris. It is expected that the damage would be substantially cosmetic and that the building would still be occupiable until tradesman became available to do the aesthetic repairs.