Built to last

The concept of future proofing is the process of anticipating the future and developing methods for minimising the effects of the shocks and stresses of future events. How does this concept apply to the construction of houses?

As Nick Gaites, an executive member of the New Zealand Institute of Building Surveyors explains, we all want a comfortable home to live in. So, when considering building or renovating we need to think about creating a healthier, safer, more energy efficient and comfortable home that’s worth more in the future. That is future-proof building espoused by such organisations as the New Zealand Green Building Council and the Passive House Institute of New Zealand.

Since 2005 when the New Zealand Green Building Council was established, futureproof building has become less of a futuristic concept and more a standard industry practice. Initially as a consequence of the leaky homes debacle of the mid-late 1990s and early 2000s, future proofing focused on weathertightness and durability. Now the approach looks more broadly at such aspects as sustainability, energy efficiency, health and safety, sound control and space management.

Weathertightness

Many factors contributed to problems with weathertightness. Poor design, poor project management and poor building practices played a role. The exposure of New Zealanders to international design trends and materials has led to a wider range of housing styles, but some house designs and materials are unsuitable to specific site conditions.

“For instance,” Nick says, “some house styles and features designed for dry climate locations have been used in areas of high wind and rainfall. Features such as parapets, decks and pergolas that penetrate a dwelling’s cladding contribute to weathertightness risks, as does monolithic cladding, low-slope roofs, membrane roofs, a lack of eaves and complex junctions, especially when these are used in wet and windy conditions.”

House claddings do leak. That becomes an issue when the water is not dealt with effectively and affects the integrity of the house. “The Canadians developed the 4Ds philosophy of weathertightness – deflection, drainage, drying and durability. In New Zealand we have adopted those principles but we now also consider airtightness, ventilation and insulation.”

The ideal is to achieve all four Ds. Deflection devises (such as cladding and window head flashings) intercept water at a building’s exterior and deflect it away from critical junctions. Wall assemblies need to be designed and built with protected cavities to incorporate drainage to allow any water that may have penetrated the exterior cladding to drain down the back of the wall cladding and out. The amount of drying that occurs depends on the cladding type and the way it is installed and all components of a cladding and wall assembly must meet the durability requirements of the Building Code.

Passive roof ventilation

“If you heat and insulate and you don’t ventilate you will condensate! In the past, roofs didn’t need to be specifically ventilated because the common claddings were inherently air-leaky. Today, with membrane and shingle roofs, things are different. That’s because 21st century homes are more airtight and if they aren’t aired, condensation may occur and mold may form.”

Moisture is constantly being added to the inside of houses from everyday activities such as cooking, taking showers and doing laundry. Nick explains that in the past this excess water was often removed from the building by natural ventilation. Draughty windows, doors and floors provided a channel to constantly replace moist inside air with fresh outside air.

With more airtight homes this moisture can find its way into the roof space, so we need specific methods of allowing continuous airflow into a building. Non-powered passive roof ventilation is one way of assisting this process thereby helping to reduce internal moisture and subsequent condensation and mold.

There are a variety of product options and combinations which will provide passive roof ventilation for new builds and existing homes. Primary roof ventilators fit externally within the eaves and at the ridge. They incorporate rows of slots large enough to allow the required volume of air to flow freely. Secondary roof ventilators fit higher up within the eaves holding down roof insulation material and preventing it from restricting the flow of air to and from the primary roof ventilator. In many cases it is wise to have both primary and secondary roof ventilators in order to provide a reliable uninhibited ventilation system.