Roofing materials for school buildings

When your school's getting a new building or replacing a roof, as a board of trustees you need to consider a range of factors that will help you choose the most suitable type of roofing material. Roofing must also be correctly installed.

Choosing roof materials

Your project manager or designer should guide you on the best roofing material when you're getting a new building or replacing a roof.

In choosing roofing materials, you should consider:

  • how the roofing will stand up to local weather conditions
  • how it can keep energy costs down
  • if it's suitable for your school’s location, for example, if your school is close to the sea, the roofing should be able to resist sea spray corrosion
  • if it matches the building’s design and type of construction
  • if it can improve the building’s appearance
  • if its cost will be within the project budget.

Reducing risks in earthquakes

Light roofing materials reduce the risk:

  • to life in a major earthquake
  • of damage to the building in a moderate earthquake.

The Ministry’s policy is that heavy tile roofs must be replaced with lighter materials when upgrading buildings.

Refer to the following page for more information about replacing heavy tile roofs.

Strengthening school buildings for earthquake resilience

Installing roofs

Roofing must be correctly installed. For example, the roof must:

  • have the recommended roof structure
  • be at the right pitch.

If it's not installed correctly, the manufacturer’s guarantees may be invalid.

Weathertightness and durability design

Find out about our design requirements for roofing materials and installation in our Weathertightness and Durability Requirements, which you can download on the following page.

Weathertightness and durability design for school buildings

Translucent plastic sheeting used in schools

Translucent plastic sheeting is a material often used in school roofs and verandas. It includes PVC, fibreglass and polycarbonate roofing products. However, you must treat this sheeting as a potential danger because of the risks that:

  • people may fall through it — a risk that increases as the sheeting ages and becomes brittle
  • it may catch fire as it can be flammable.

It's good practice to take measures to stop people from climbing on the sheeting. For example, don’t have any structures close by that can be easily climbed.

Installing translucent plastic sheeting

To manage the risks of installing plastic sheeting, we have some specific installation requirements which you must follow.

Make sure your suppliers and installers are aware of them. As new products enter the market, suppliers, installers or project managers may suggest some of the measures below are not necessary. Talk to your property advisor about getting an exemption.

Rules for safety netting or mesh

Some translucent sheet materials are classified as ‘trafficable’. When using these products, safety netting is not required. (Netting can be unsightly, deteriorates if un-washed and may be distorted through vandalism.)

To qualify as trafficable

To qualify as trafficable the material must:

  1. comply with AS/NZS 4256.3:1994: Plastic roof and wall cladding material
  2. have a UV resistant coating to protect against surface erosion
  3. have a minimum 20 year warranty protecting against surface deterioration and maintaining trafficability, and
  4. have a BRANZ Appraisal or CodeMark product certification.

AS/NZS 4256.3:1994 — Standards NZ website (external link)

BRANZ Appraisal — BRANZ website (external link)

CodeMark product certification — website (external link)

Using non-trafficable sheets

If the sheets are non-trafficable, they must be laid over netting or mesh. The netting or mesh must be:

  • strong enough to hold the weight of an adult if the sheeting gives way
  • plastic coated where possible, especially in areas exposed to the elements
  • fitted in the opposite direction to the run of purlins – these are the beams on the roof that the sheeting is fixed to — and the purlins must also be placed no more than 1200mm apart before horizontal timber spacers are required.

Rules for Fire Group Classification

The Building Code requirements for internal surface finishes are given as Group Numbers (Clause 3.4(a) of the Code). This may be known as ‘Fire Group Classification’. It represents the measure of how much smoke a material gives off when it burns. It's important that products used inside don't exceed these limits because the amount of smoke affects how easily people can escape. There are no Fire Group Classification requirements for products used outside because the smoke can disperse.

Learn more about Achieving NZBC Group Numbers for surface finishes from tests to overseas standards.

Rules for roofs, covered walkways and verandas

Exterior application

Translucent sheets are often used on open-sided structures on the exterior of buildings (verandahs) or between buildings (covered walkways).

For exterior application, where the translucent sheeting is:

  • non-flammable or self-extinguishing, there's no restriction on its continuous use
  • flammable, each sheet must be separated by a sheet of metal roofing.

Interior application

Translucent sheets used within buildings and directly exposed to the interior spaces (including walkways or verandahs with side-walls, ie where smoke can accumulate) have the following requirements:

  • Products with a Fire Group rating of 2 must be used.
  • Where the material is:
    • non-flammable or self-extinguishing, there's no restriction on continuous use of the material
    • flammable, each sheet shall be separated by a sheet of metal roofing.

Rules for walls

When installing translucent plastic sheeting to walls, position the sheets at least 2 metres above external ground level, or 2 metres above internal floor levels, whichever is higher.

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