Updated design requirements for new schools

This Issue This is a part of the Weathertightness feature

By - , Build 183

Updated weathertightness requirements for designing new school buildings have recently been released by the Ministry of Education. These include the knowledge and expertise gained from remediation projects.

Figure 1: Updated Ministry of Education design requirements for sheltered and exposed threshold channels.

AS A LONG-TERM property owner, the Ministry of Education has specific weathertightness design requirements that have been in use since 2011, some of which exceed the New Zealand Building Code.

The latest edition was launched in September 2020 and provides project teams with the required attributes for the design of the external envelope of new school buildings.

Evolution of school designs

The Ministry is the second-largest social property owner in New Zealand with over 15,000 buildings spread across approximately 2,100 state school sites. At 30 June 2020, the replacement value of the portfolio exceeded $31 billion.

Many school buildings were designed and built between the 1950s and the mid-1980s under the Department of Education and Education Boards. Generally, these were 1 or 2-storey timber-framed, standardised designs.

The approach to designing and building schools changed from 1989 with the implementation of Tomorrow’s Schools reforms, which gave school boards more responsibility to manage their school property and led to more bespoke building designs.

The way we design and build schools has continued to evolve, and there is now more emphasis on spaces that support a variety of teaching and learning practices. These buildings typically feature wider structural spans to provide higher levels of connectivity between the internal teaching and learning spaces and greater ability to reconfigure buildings over their lifespan.

Last year, the Ministry released its Te Rautaki Rawa Kura – School Property Strategy 2030, which aims to ensure all schools can access quality learning environments by 2030.

Part of this includes moving towards higher levels of sustainability within a well-managed portfolio.

Weathertightness remediation informed changes

In response to significant weathertightness issues with buildings built or modified after 1994, the Ministry’s Building Improvement Programme was established in 2009 to address the weathertightness failures in school buildings.

The knowledge and expertise gained from remediating over 500 buildings helped the Ministry to develop a revised approach to weathertightness remediation resulting in the launch of the Weathertightness Remediation and Regulatory Strategy in July 2018.

The backbone of this is responding to actual and proven weathertightness failure and damage that has been validated through remediation inspection reports undertaken by Ministry-briefed building surveyors.

These reports provide design teams with a guiding scope of work for remediation. In addition to completing the building consent and construction documentation, architects and designers are required to undertake appropriate levels of on-site observation to ensure the construction works comply with their designs.

All remediation inspection reports and designs are also independently reviewed by a Weathertightness Review Panel. More information on this is available on the Weathertightness Remediation webpage.

Practical design requirements

The Weathertightness Design Requirements for New School Buildings have been updated based on recent industry developments and feedback received from completed projects. They are also based on practical design requirements that capture the knowledge and expertise from the Building Improvement Programme, completed remediation projects and over 300 remediation inspection reports competed to date.

Roofs and claddings exceed Code minimums

Since 2011, school design requirements have exceeded the New Zealand Building Code in several areas including increased roof pitch and specific drained and ventilated wall cavity requirements.

External envelope cladding systems are now required to have a serviceable life that, with normal maintenance, will be the life of each building. This exceeds the Building Code’s 15-year lifespan on cladding systems and has been done to avoid cladding systems that require major remediation or replacement or excessive or difficult maintenance.

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Providing accessibility at external doors

The update also addresses the potential conflict between important accessibility requirements at external doorways and the need to maintain a weathertight enclosure.

E2/AS1 requires a 150/225 mm step down between the internal floor level and the external paving/ground levels. However, there can be a conflict at external doorways where level access is required to achieve accessibility requirements. In some cases, this has created an undulating effect with the paving rising and falling between adjacent sets of external doorways.

The updated requirements offer solutions and diagrams to help navigate this potential conflict. These include allowing threshold channels between two or more external doorways to be connected provided the doorways are protected by large verandas or a suitably wide overhanging storey above (see Figure 1).

Figure 1: Updated Ministry of Education design requirements for sheltered and exposed threshold channels.

Key changes in the new requirements

There are several other key changes in the updated requirements for new schools:

  • Cladding systems cannot rely on sealant at their junctions – mechanical flashings are required.
  • Rigid air barrier board is a mandatory requirement for all external framed cavity walls.
  • Concrete external walls require design or review by a façade engineer to address condensation issues caused by thermal bridging.
  • Warm roof forms of construction are required for all new buildings with steel roof structures to help mitigate condensation issues caused by normal and aggravated thermal bridging.
  • Roof rainwater collection points are to be positioned at least 600 mm from the external face of the building to prevent water entering the external wall cavity.
  • Internal gutters and roof level parapets are no longer permitted due to the observed poor weathertightness performance.

Keeping up with industry

With the support and feedback of architects, designers, building surveyors and other industry specialists, we continually update and improve all our design requirements. This has meant that, as well as aligning with current industry trends and practice, our updated weathertightness requirements promote:

  • more robust and cost-effective buildings
  • less maintenance over the building’s life
  • simple and straightforward building forms
  • elimination of poor-performing building materials and systems
  • consistency with our aims as a long-term building owner.

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The Ministry will further update this document as required and welcomes feedback at [email protected]

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Articles are correct at the time of publication but may have since become outdated.

Figure 1: Updated Ministry of Education design requirements for sheltered and exposed threshold channels.