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*ARCHIVE* - Barriers - The sky's the limit

Clause F4 "Safety from falling" is the main focus of the New Zealand Building Code requirements for barriers. Other clauses that affect barriers are B1 "Structure", B2 "Durability" and F2 "Hazardous building materials".

A barrier does not have to be built in accordance with the Approved Documents . If it is not, however, the owner, designer or manufacturer has to show the territorial authority that the design complies with the relevant clauses of the building code. A sure way of demonstrating compliance is to show the barrier is as good as the acceptable solution. Tests and standards other than those named in the verification methods and acceptable solutions may also be used, but the territorial authority will want to know what relevance or standing they have. Sometimes compliance can only be shown by asking the following questions:

  • "What is required by this clause?" followed by,
  • "Does my design satisfy those requirements?"

Structure

NZBC Clause B1 "Structure" requires barriers to withstand the combination of loads that they are likely to experience during construction or alteration and throughout their lives. The performance criteria give a list of likely loads and other factors that must be considered when assessing the stability of a barrier.

The Verification Method B1/VM1 cites the loadings Standard NZS 4203 as the source of loads. B1/VM1 requires NZS 4203 to be used in conjunction with the appropriate materials Standard (steel, concrete, masonry or timber) to design a barrier. Currently the aluminium Standard AS/NZS 1664: 1997 Parts 1 and 2 is not cited in the Approved Documents. Until it is, that Standard can be proposed to the territorial authority as an alternative solution.

Acceptable Solution B1/AS2 provides one design for a timber barrier. For a barrier incorporating glass, B1/AS1 identifies NZS 4223 as an acceptable solution for the sizing of glass to carry loads resulting from wind and human impact.

Durability

Building code Clause B2 "Durability" requires that Building materials, components and construction methods shall be sufficiently durable to ensure that the building satisfies the other functional requirements of this code throughout the life of the building.

The performance criteria for B2 "Durability" gives the period of time for which parts of a building must be durable. Generally, Clause B2.3 requires a barrier to have a durability of 15 years. Any protective coatings and easily accessed and replaced attachments to a barrier will require a durability of 5 years. If, however, a barrier contributes to the structural stability (ie, provides bracing or support to the building) or is in an inaccessible situation or its failure would go undetected, it is important to check the durability classification. Clause B2.3 may require the barrier to last the life of the building (but not less than 50 years).

Hazardous materials

The requirements of building code Clause F2 "Hazardous building materials" are that building materials which are potentially hazardous, shall be used in ways that avoid undue risk to people.

Acceptable Solution F2/AS1 quotes NZS 4223: Part 3 with some modifications as a means of complying with clause F2 for glazing in barriers likely to be subject to human impact. Requirements for wind loading might exceed those for human impact so it is necessary to check both.

Safety from falling

The requirements of building code Clause F4 "Safety from falling" are that buildings shall be constructed to reduce the likelihood of accidental fall.

The performance criteria F4.3.1 outlines the situations where barriers are generally required: Where people could fall 1 metre or more from an opening in the external envelope or floor of a building, or from a sudden change of level within or associated with a building, a barrier shall be provided. (Except where a barrier would be incompatible with the intended use of an area or it is a temporary barrier on a construction site where the possible fall is less than 3 m.)

F4.3.2 and F4.3.3 are more specific about two situations: Roofs with permanent access shall have barriers provided and Swimming pools having a depth of water exceeding 400 mm, shall have barriers provided. (Does not apply to any pool exempted under section 5 of the Fencing of Swimming Pools Act.)

In F4.3.4 the physical requirements of barriers are set out:

  1. Be continuous and extend for the full extent of the hazard,
  2. Be of appropriate height,
  3. Be constructed with adequate rigidity,
  4. Be of adequate strength to withstand the foreseeable impact of people and, where appropriate, the static pressure of people pressing against them,
  5. Be constructed to prevent people from falling through them, and
  6. In the case of a swimming pool, restrict the access of children under 6 years of age to the pool or immediate pool area.
  7. Restrict the passage of children under 6 years of age when provided to guard a change of level in areas likely to be frequented by them.


F4.3.5 gives additional requirements for barriers to swimming pools:

  1. All gates and doors fitted with latching devices not readily operated by children, and constructed to automatically close and latch when released from any stationary position 150 mm or more from the closed and secured position, but excluding sliding and sliding-folding doors that give access to the immediate pool surround from a building that forms part of the barrier, and
  2. No permanent objects on the outside of the barrier that could provide a climbing step.

Potential for variation

Of all the building elements used in building, barriers probably have the potential to vary the most as a design element while following acceptable solution F4/AS1. For instance, while the acceptable solution gives restrictions on height, size of openings within a barrier, and positions of toeholds, it does not generally restrict the materials that can be used.

Sometimes it is appropriate that the height is not within the parameters of the acceptable solution. In such cases, an alternative solution may be accepted if the territorial authority is satisfied that it complies with the building code. A climbing platform for a kindergarten, creche or daycare centre could have a rail that is much lower than the standard 1000-mm-high barrier and comply with the building code clause F4 requirement for an appropriate height. The figure of 1000 mm is based on the average height of a male hip as the pivot centre for falling over a barrier when leaning. If a platform is only to be used by small children the height of the barrier could be reduced quite safely and still comply.

Barriers that fall outside the parameters of the acceptable solution do cause difficulty. If the height, size of openings within a barrier, or the positions of toeholds do not follow the acceptable solution the designer must use other methods to ensure that the barrier complies with the building code. BIA staff cannot themselves give binding alternative solutions, although the Authority can rule (by way of formal determination) that an alternative solution is to be accepted by a territorial authority for a particular building. A territorial authority is able to approve an alternative solution for a barrier if it is satisfied that the proposal will comply with Clause F4. Some alternatives that BIA staff have heard about contain tightly spaced horizontal members, wide ledges that project inwards, raised planter boxes, and barriers with a wide top that have a surface construction that would be difficult for children to walk along.

Toeholds

Acceptable solution F4/AS1, in paragraph 1.2.1(b), requires barriers in areas frequented by children under 6 years old to have no components between the heights of 150 mm and 760 mm above floor level which can provide a toehold.

An alternative solution that might be considered by a territorial authority is a 1000 mm high barrier with no toeholds between the floor and 610 mm height (760 – 150 = 610). Possibly a barrier of such construction would be more difficult for a child to climb because the reach to the top of the barrier is greater with a foot at floor level than at 150 mm above the floor.

The Authority may be making a formal determination in this matter in the near future, which would provide a definitive answer.

Amendments

The latest amendments (February 1998) to the acceptable solution for F4 include changes that recognise mesh, perforated sheet or trellis as complying if they are rigidly fixed over the full barrier height and the openings measure no more than 50 mm (other than the perimeter).

Windows can also create a situation where safety from falling is required (they are after all openings in the external envelope). This is recognised in a new paragraph requiring either a minimum window sill height, a window opening restrictor, or a barrier located in front of the window with limitations on toeholds. The amended F4/AS1 has all the details.

Over water

A barrier is not required where it would be incompatible with the intended use of an area. The Authority, in a determination, said a working wharf does not need a barrier.

When considering the requirement for a barrier above water, the distance that a person might fall is measured not to the surface of the water but "to the underlying ground, or at least to the depth at which the falling person starts to float". This was said as part of a High Court judgment about a floating marina. Thus the depth of the water as well as the distance to the water must be taken into consideration.

Pools

The Schedule to the Fencing of Swimming Pools Act 1987 is identified in Acceptable Solution F4/AS1 as a means of compliance with the building code. A barrier around a pool needs to be more child-proof than other barriers in and around buildings. The main difference in the fences needed for decks and balconies and those for pools is the height. A pool fence has to be 1.2 m or 1.8 m high depending on the construction and how well that construction restricts children from falling. It pays to discuss any variations from the Schedule with the territorial authority before detailing is very far advanced. (See previous articles in BIA News Nos 33, 36, and 72.)

Waivers

Most building code provisions may be waived in certain circumstances. The territorial authority can waive provisions of Clause F4: for example, where a new barrier is to join an existing but non-complying barrier and there is free movement between the new and existing deck areas. Of course the relative proportion of existing to new barrier, the difficulty of compliance, and the comparative danger must be considered when granting a waiver such as this.

Section 47 of the Building Act outlines matters for consideration by territorial authorities in relation to exercise of powers and can be used to give guidance for waivers. Some territorial authorities have also given waivers from Clause F4 for Department of Conservation walkways in remote areas where the height of fall is relatively small but still more than 1 m.

The sky's the limit

  • Be aware of the performance criteria of Clause F4 of the building code
  • Think outside the square
  • Discuss alternatives with your territorial authority at the design stage.

Architects and designers are starting to produce a variety of barriers to fit all sorts of situations. Territorial authorities are becoming more aware that the building code is not restrictive regarding barrier design and innovative designs can comply.

Show and tell

We've heard that good examples of innovative barriers have been accepted by territorial authorities around the country. Send in photos of such barriers and BIA News will publish a selection of them.

Standards mentioned

  • NZS 4203: 1992 General structural design and design loadings for buildings.
  • NZS 4223: Code of practice for glazing in buildings. Part 1 and 2: 1985, Part 3: 1993.
  • AS/NZS 1664: 1997 Aluminium structures. Part 1 and 2.
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