Decks and balconies - playing it safe

Decks and balconies supported by untreated, kiln-dried timber may pose a safety risk, particularly where water pools rather than drains away.

This information was confirmed as current in February 2016. It originally appeared in Codewords newsletters prior to January 2014.

  • Of interest to Homeowners, Building consent authorities, Designers,

Decks and balconies more than 1.5 metres above the ground need a building consent. However, even consented balconies could be unsafe. They must also be maintained throughout their life.

Certain types of timber construction are of concern. In particular, there is risk of timber decay where water can be trapped within timber balustrades enclosed by cladding or where the floor is covered with a waterproof surfacing, with or without tiles laid on it.

Unless the deck or balcony has been correctly designed, constructed and, most importantly, properly maintained, water may leak in behind the cladding or through the waterproof surfacing and create conditions that encourage timber to decay and fasteners to corrode.

Risk factors

Owners of properties with a balcony or deck should consider whether any of these risk factors exist:

  • untreated, kiln-dried timber used for structural support
  • a balustrade clad with lightweight materials with a plaster finish
  • holes or cuts in the waterproof floor surfacing
  • flat access, with no step, where the deck meets the building doorway
  • water ponding on the surface
  • cantilevered joists (or other joists that penetrate the exterior wall) lacking flashings.

Owners should also inspect the barrier or balustrade as there may be further risk if it:

  • is clad with lightweight material with a plaster finish
  • lacks a waterproof capping
  • has a flat top where water sits
  • has a railing where water is able to leak down screw holes.

Warning signs of possible danger include:

  • balconies and decks move when walked on
  • damp spots or stains where the balcony, balustrade or deck joins the main part of the building
  • cracks, particularly near junctions, joints and corners
  • balustrades or railings that wobble
  • balustrades where damp spots or stains can be seen on the cladding
  • interior water damage or any visible change to interior finishings adjacent to or directly beneath the balcony or deck.

Open timber decks

Open timber decks constructed with durable, treated timbers are less likely to be of concern, but the following checks should be made.

  • Look at where the deck meets the wall of the house.
    • Is there anywhere that water can sit or track into the house?
    • Do the flashings take water away from the house wall and allow it to drain away?
    • If the cladding relies on paint to keep the water out, is that coating continuous or is there any point where water might penetrate?
  • Is there any sign of timber beginning to decay? For example, is there any sign of excessive cracking or 'softness'?
  • Is there proper waterproofing around the cantilevered joists or around other joists that penetrate the house wall?
  • Are the balustrades or posts correctly connected to the deck or balcony structure? They should not wobble.
  • Are bolted connections tight, especially on balustrades and handrails?
  • Are any galvanised steel connectors corroding?

You can get further information about deck or balcony safety issues from:

All guidance related to B1 Structure

This information is published by the Ministry of Business, Innovation and Employment’s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: