What are the best windows for New Zealand Houses?

Passive ventilation allows rooms to ventilate while windows and doors are closed. The system is completely built into the window, hidden from view.

Wind zones

'Wind zones' are calculations of the wind load buildings can expect to be put under. Wind speed, you see, is another important consideration when choosing windows - the last thing you want is to submit plans to the council only to have them declined. In addition, a lack of strength, or a poorly located window can result in it being constantly blown open or shut.

That said, just because you're in a high-wind-speed area of the country doesn't mean you can't have operable windows. 

Part 2: Comparing window frame and glass options

Window frame materials

There are three common window frame materials used in New Zealand: aluminium, PVC and wood. Your choice of the frame could have a big impact on the function, durability and performance of the entire unit. For example, a thermally broken aluminium frame can reduce heat loss by up to 20% (compared to a standard aluminium frame, according to Energywise).

At Altus Window Systems, we generally use aluminium for our windows and doors. Why?

1. Durability: Aluminium is a hardy material that is resistant to wear and tear. It is also corrosion and water-resistant, typically lasting many years without swelling, cracking or warping.
2. Performance: Aluminium windows and doors are manufactured to high modern standards, and can come with features such as a thermal break.
3. Maintenance: Thanks to its durability, aluminium requires little maintenance over its lifetime.
4. Aesthetics: Aluminium is a modern, stylish material that can be finished in many different colours and styles.
5. Sustainability: Aluminium is 100% recyclable.

Sizes and styles

There's a lot to consider when you're looking at the size and style of window you want in your new home. A bigger window will offer more of a view but may let in more solar heat in summer. Windows that can't open will offer no ventilation benefits, but also won't blow open or shut on a very windy day.

To help you understand more how size and style can impact day to day function of the window, here are some ideas to think about:

1. Placement: If chosen incorrectly, windows can blow open or closed in high winds, or impede the function of other features of your home (e.g. an adjacent sliding door). If you want a window that is easily opened but is on the side of the prevailing wind of the property, you might choose an awning or sliding window instead of a casement as these are less likely to slam.
2. Ventilation: You must be able to ventilate your home to reduce internal air moisture. In fact, opening a window 300 mm for just 10-15 minutes can reduce air moisture in that space by as much as 14%, according to a BRANZ study. So you need operable windows throughout the house to create a cross breeze. If wind or rain is a problem and you don't want large opening windows, you could consider a hopper or smaller awning window at the top of a fixed panel instead. Or if you live in a very hot area and need the passive cooling that can come with gentle winds, consider instead large sliding windows and doors across the property, for instance in the living room/kitchen and in the master bedroom. Further options include louvres and passive ventilation, both of which can control airflow even while windows and exterior doors are closed.

For a better understanding of how placement, size and style might impact your new home, we recommend talking to the Altus Windows system supplier experts for specific advice.

Even in a modern, well-insulated home approximately 50% of the interior heat can be lost through single glazed windows.

Glazing

You probably know that double glazing is considered 'better' than single glazing, but does that mean triple glazing is better than double? Actually, no. Double and triple glazing are indeed better insulators than single glazing, this is true, but remember every decision you make has to be right for you.

How double and triple glazing works

When heat tries to pass through the window, it hits an air pocket between the panes and becomes trapped. This trapped air then creates a thermal barrier against further heat loss.

So when might you not choose triple?

In some cases, for example in areas where sun exposure will be a regular and important factor, triple glazing might 'over-insulate' your home. If the heat gets in and can't get back out, the room gets warmer and warmer. In this scenario, it might be better to have a double-glazed unit with a low-E coating (see below) - you'll still get some passive heating, but the bulk will be rejected and the rest can filter back out again.

Again, this is where we recommend you speak with an expert. A knowledgeable window and door professional can help you understand building performance and how the various factors discussed today will affect your home.

Special extras

Before we wrap up, there are a couple of other considerations to factor at the choosing stage.

Low-E: Low-emissivity glass (low-E for short) includes a polyester film that is stuck to the glass to reflect radiant heat, such as that from the sun. It can be placed inside or outside the window glass, depending on whether you want to block or trap heat.

Argon gas: Double- and triple-glazed can be filled with argon gas instead of regular air. Argon is denser than air, which means air has a harder time passing through. This can improve the thermal efficiency of the unit. Importantly, argon is odourless and colourless and is completely safe.

Comparative glass types – performance for heat loss reduction

Thermal breaks: A thermal break is either a resin-filled channel or polyamide strip inserted between the inside and outside aluminium profiles of your window. The thermal technology prevents heat or cold transferring from the inside frame to outside and vice versa.

There is a variety of thermally enhanced joinery systems which add insulation to your windows and doors. The Altus Window Systems All Seasons (left) uses a 'pour and de-bridge' thermal break while the Pacific Thermal system (right) uses a 'polyamide strip' thermal break.

Part 3: Putting this all together

Now that we know the basics, let's finally answer our big question.

The best windows for a New Zealand home are those chosen to suit the unique climate of the specific area. Areas of high humidity need lots of ventilation, areas of high sun exposure can benefit from low-E coatings and sunshades, areas of extreme cold need greater thermal performance and must capture passive solar heat gain, and areas of high wind may require window designs to limit them slamming open or shut.