BC Update: No.94 - Safety reminder: decks, balconies and balustrades

January 2009: The Department of Building and Housing reminds owners of dwellings that decks and balconies supported by untreated kiln-dried timber may pose a safety risk, particularly in those situations where water pools rather than draining away.

At this time of year, many New Zealanders take advantage of warmer weather and time off work to have barbecues and socialise. They often enjoy these occasions on their decks and balconies.

This summer season, it is worth taking some time to consider that certain types of decks and balconies do have a risk of rotting when water has leaked into them, potentially leading their underlying structure to decay. In extreme cases, this can lead to collapse.

The Department of Building and Housing reminds territorial authorities, designers, builders, building consultants and other building professionals to pay particular attention to this risk whenever they are on site.

Safety check - enclosed decks, balconies and balustrades

All types of deck, balcony and balustrade must be designed and constructed to meet the requirements of the New Zealand Building Code and be maintained throughout their lifetime.

The main concerns about leaking are with certain types of timber construction. There is potential risk of decks leaking where the timber balustrades are enclosed within claddings or the floor is covered with a waterproof surfacing, with or without tiles laid on it.

Unless 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.

If the property has a balcony or deck, consider these risk factors.

• Has untreated kiln-dried timber been used for structural support?
• Is the balustrade clad with lightweight materials with a plaster finish?
• Are there any holes or cuts in the waterproof floor surfacing?
• Is there flat access, with no step, where the deck meets the building doorway?
• Does water pool on the surface?
• Do cantilevered joists (or other joists that penetrate the exterior wall) lack flashings?

Look at the barrier or balustrade. These factors all pose further risk.

• Is it clad with lightweight material with a plaster finish?
• Does it lack a waterproof capping?
• Does it have a flat top where water sits?
•  Does it have a railing where water is able to leak down screw holes?

Warning signs

• Balconies and decks that 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 constructed with durable treated timbers are less likely to be of concern. However, these are things that should be checked.

• 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.
• Check the tightness of bolted connections, especially on balustrades and handrails, to ensure nuts are secure.
• Check that galvanised steel connectors are not corroding.

Does work on a deck or balcony require a building consent?

A building consent is not required for decks and balconies where it is not possible to fall more than 1 m should the structure collapse. However, all decks and balconies must be built in accordance with the Building Code to ensure they are safe for people to use.

Where necessary, the building work owner should apply for a building consent when constructing a deck or a balcony. The consent will give assurance that any safety concerns with the deck are addressed, as a building official will have inspected the work after it has been completed to certify that it meets Code requirements.

Building owners and building professionals should discuss this with their local council.

For more information phone:

BRANZ Advisory Helpline - 0900 5 90 90

Institute of Building Surveyors - 0800 113 400

Or call your local city or district council.