Glazing overview

Ideally, the glazed areas in your home should provide insulation and help to keep indoor temperatures at comfortable levels.

Glazing can also help keep out noise, provide ventilation without draughts, admit natural light without glare or fading your curtains/furniture, contribute to your home's safety and security, and look good. Investing in the best glazing options will also pay off in the long term with lower heating and cooling costs.

The right glazing options for your home will depend to a large extent on the climate and microclimate of your site. Wind, temperature, sun angles and proximity to the coast will all influence decisions about the size, type and placement of glazed areas.

There's a lot to consider: it may pay to speak with your designer, builder or your window supplier about best options for you.

When to think about glazing

Designing a new home or renovation

If you're designing a new home or renovating an existing one, you or your designer will need to make decisions about the types of windows, doors and skylights you'll have, how big they are, where they go, and what type of glass and frames are used.

Glazing should be considered early in any design process, as the size and placement of windows can affect other decisions such as the type of framing needed (for example, large windows in a high wind zone will place extra demand on framing).

You may be able to get cheaper prices on double glazing or special types of glass by buying a houselot.

Maintaining an existing home

You can make your home more comfortable and reduce your heating/cooling costs by replacing the windows with double glazed ones, or by choosing another option such as fitting secondary glazing or having solar film installed on existing windows. You'll also benefit if you repair windows to improve airtightness.

Buying a home

When you're buying a home it's worth thinking about windows and other glazed areas - badly designed or poorly made glazing could make a home less comfortable, secure and enjoyable to live in.

Comfort and energy-efficiency

In a well-insulated home, the biggest source of heat loss is through glazing. In winter, heat can escape through the glass or framing of windows, doors and skylights. It can also escape through air leaks around glazing that isn't airtight. In summer, windows, doors and skylights can let too much heat in.

Excessive heat loss or heat gain can make your home uncomfortable and your heating/cooling bills larger than they need to be.

To prevent excessive heat loss and heat gain:

• double glaze your windows (or, for an existing home, install secondary glazing)
• install low-emissivity glass (also known as Low-E glass) - it prevents warmth from escaping from your home and can be used in combination with double glazing
• use window frames with good insulation properties, such as timber frames or thermally-separated metal window frames
• make sure your glazing is airtight (you can have vents in the frame to allow small amounts of air to circulate - with vents, you?re in control of the amount of air getting in)
• use close-fitting, thermal-lined curtains to keep warmth in at night
• look for windows and other glazing with low U values, high R values or a high star rating from BRANZ's Windows Energy Rating System (WERS)
• if possible, make sure most of your home?s glazed areas face north to make the most of the sun and don?t have excessive amounts of glass facing in directions that don?t get much sun
• don?t have windows that are so high that their tops are permanently shaded by your home?s eaves.

If overheating is a problem, you'll need to find ways to provide shading and improve ventilation. You may also want to consider tinted or reflective glass, or solar control film on your windows. See double glazing and glass options for more.

Natural light

Natural lighting makes your home healthier and reduces the need for/cost of electric lighting. Diffuse lighting (as opposed to direct sunlight) provides good illumination without glare.

Window size and orientation is also important for lighting. In summer, west-facing windows may be sources of glare and overheating unless some form of shading is provided.

Fading

Some interior furnishings fade when they're exposed to sunlight. To prevent fading, you may want to consider using reflective, tinted or spectrally selective glass to prevent heat gain (see double glazing and glass options for more).

Ventilation

Effective ventilation depends to a significant extent on the size and placement of windows and other openings.

Some framing systems include built-in air vents for air circulation while the window is closed.

Side-opening casement windows and top-opening awning windows can be used to direct breeze inside. Sash or vertical sliding windows encourage ventilation and cooling by allowing cold air in at the bottom and/or warm air out the top.

Louvres with glass, timber or metal blades can provide ventilation in sheltered areas - but they're less airtight than other options.

Condensation

Condensation occurs when water vapour inside your home comes into contact with cold glass or metal framing. The most effective way to reduce condensation is to ensure your home is well ventilated.

Fitting double glazing and well-insulated window/door frames can significantly reduce condensation on and around windows and glazed doors - but you will still need to ventilate.

Noise

Standard, single-glazed windows are poor noise barriers. Double glazing provides some improvement. If noise is a problem, laminated glass can reduce noise levels significantly. Opening the windows will increase noise levels, so you'll need to consider the best way to manage ventilation when noise is an issue.

Safety and security

Toughened safety glass and laminated glass are both safer than standard glass, and harder for intruders to break. Under the Building Code, safety glass has to be used in some areas.

For security, you'll also need to consider the strength of window and door frames.

Some types of window and door may be more suitable in windy areas. French and hinged doors can be caught by strong wind gusts. Sliding and stacker doors are less likely to be caught by the wind.

If a window opens over a path or other traffic area, there's a risk someone might walk or run into it. Sliding windows might be more suitable than hinged ones in this situation.