This July, BRANZ will publish another bulletin – BU701 Building on land subject to flooding and/or landslides – that’s essential reading for anyone building on a site known to be at risk of flooding or landslides.
The bulletin summarises the key considerations, regulatory frameworks and requirements that relate to designing and building for resilience against these hazards. It looks at how the Building Act, Building Code, NZS 3604:2011 Timber-framed buildings, Resource Management Act, district plans and other local requirements govern what resilience measures may or may not be taken.
Broad approaches and detailed design tips
The new bulletin also offers practical ideas for building resilience into all aspects of design. It covers broad principles – such as options for locating a building on a flood-prone site – as well as ways that flood-resilient design can be introduced to the individual components and features that make up the building and property.
At the broad scale, the bulletin advises identifying and then building away from natural drainage paths or channels on the site and locating the building on the highest part of the property whenever practicable. Existing vegetation should be retained where possible too – especially mature trees, which can play a significant role in stormwater management.
At the component level, flood-resilient design involves making use of materials, construction systems and house styles that can withstand substantial and multiple floods. Flood-resilient design allows homeowners to remove and store belongings before a flood and then clean up and repair after floodwaters recede with less disruption.
The bulletin offers some specific ideas:
- Design a piled rather than a flat concrete slab foundation to create a higher floor level and allow a home to be relocated more easily if needed.
- Install utilities such as water heating cylinders on a raised platform rather than on the floor.
- Specify flooring materials with high resilience such as compressed fibre-cement, hardwood floorboards or plywood rather than particleboard or strand fibre products.
- Specify flood-resilient skirtings and solid doors rather than hollowcore doors.
- If there are staircases, make the bottom riser of stairs removable for easy cleaning and drying out.
- Use flood-resilient cabinetry in kitchens and bathrooms.
- For homes on sloping ground, try to avoid sealed driveways directing surface water towards the house.
- Specify permeable paving for driveways and paths.
- Ensure that paved and unpaved surfaces within 2 m of a home direct stormwater away from the home.
The bulletin also lists multiple sources of additional information.
CRESA tool: storms, floods and heavy weather
A wealth of practical advice and checklists are also offered in a tool produced by CRESA with support from BRANZ – Resilient Homes: Storms, Floods and Heavy Weather (see For More below).
The tool notes that a resilient house features simple design, materials and systems. It highlights how the siting of a house matters too. For example, a house oriented to catch the sun can make a big difference if electricity is cut during a storm and there’s no alternative energy source for heating and lighting.
Included are useful rating scales that enable designers, builders or buyers to assess resilience component by component as they design a new building or review an existing property.
What the tool covers:
- Roofs – the complexity of roof design and the condition of guttering and downpipes significantly affects resilience in heavy weather.
- Skylights – these can be a weak link during storms and other high wind events. They can be broken by debris and vulnerable to wind-driven rain.
- Canopies, verandas, decks, porches, lean-tos and additions – add-ons like these can be a problem if they are weakly connected to the main dwelling, poorly detailed or poorly maintained. They can be damaged in high winds because they alter the air pressure around the house.
- Windows and glass doors – glass components can be broken by windblown debris or wind pressure.
- Walls and wall claddings – simple is best. A house with multiple junctions and lots of different claddings requires more maintenance and can be harder to repair if damaged in a storm.
- Exterior doors – like windows, doors tend to be weaker than walls so can be vulnerable to windblown debris and can fail at much lower wind pressures than walls.
- Wiring and electrical systems – these can be very vulnerable to water. Resilient houses have plugs and switches set at least a metre above the floor and avoid running wiring under the floor.
- Heating, cooking, lighting and water – a house that’s not always dependent on reticulated water and electricity will be more resilient.
CRESA has developed another helpful tool that rates the resilience of different styles of typical building components such as flooring, insulation, wall claddings and doors (see For More below).
Building above Code
Another new online portal, Design.Resilience.NZ, is a one-stop shop of resources for those who want to design buildings that go above the structural requirements of the Code. Most of the resources relate to building for resilience against earthquakes and include, for example, guidelines for designing seismic isolation systems, advice on hollowcore floors and BRANZ’s code of practice for seismic performance of non-structural elements.
The portal is an authoritative source of recognised non-regulatory design and construction documents and a valuable source of information for designers and practitioners. It is a joint undertaking between NHC, MBIE, BRANZ, New Zealand Geotechnical Society, New Zealand Society for Earthquake Engineering and Structural Engineering Society of New Zealand.
Shifting the seismic focus
Aotearoa’s current seismic design standards focus mainly on saving lives. However, recent earthquakes have highlighted the need to update those standards so they also protect property and reduce economic impacts after a seismic event.
New research led by BRANZ is working towards revising the seismic loading standard and developing a new framework for building performance that aims to protect property as well as people.
That same principle underpins a new resource recently launched by NHC in collaboration with MBIE. The Low Damage Seismic Design resource will eventually comprise three volumes of technical advice on designing buildings that perform better in an earthquake, ensuring the buildings can continue to be used after the shaking stops.
The aim is to support building owners, developers and design teams who want building designs that:
- lower the potential risk of earthquake damage to a new building
- reduce the time it takes before a building can be used after an earthquake
- provide sustainability benefits such as fewer repairs and reduced likelihood that a building needs to be demolished after a major earthquake
Volume 1 of the resource was released earlier this year and sets the scene by explaining concepts and terms, outlining the value of the approach, advising on how to start and explaining the limitations of seismic performance of buildings designed to the New Zealand Building Code. Volumes 2 and 3 are expected to be released later this year.