Want a warmer home in winter?  Moving from a house with single glazing, standard double glazing or want to RetroFit Double Glazing into you home.  Metro have options to suit your needs and budget. 

While the New Zealand Building Code sets out the minimum legal insulation performance requirement to build, many homeowners are increasing the thermal performance of their windows and window system in their homes.  While the current building windows requirement is consistent across the current three climate zones, this is set to change.  Currently, under consultation the new building code is due to come into effect in November 2022.  This will see changes in the climate zones moving from 3 to 6, and higher window performance levels across those in most if not all the zones.  In light of these changes if you’re unsure of what double or triple glazing will best meet you thermal insulation needs feel free to contact us.

The key technology for keeping homes warm in the winter is Low E double or triple glazing.  Low E is the shortened version of the term Low Emissivity.  Low Emissivity is the ability to radiate the long wave heat energy away and back into the home, rather than pass through the window to the outside, often called heat loss.  Using Low E glass within double and triple glazing can make your home more comfortable because it helps keep the warmth in and internal temperatures within the ideal range of 20-22C. You will enjoy year-round comfort and lower energy bills to boot.  To find out how Low E works look here

While Metro has been servicing the New Zealand market with Low E coated glass for the last 20 years the original coatings were but a steppingstone to the new soft coat technology.  With the old hard coat technology producing a hazy effect when looking through the glass. 

Tried and proven the Metro glass soft coat Low E range has continued to evolve since its inception in 2013, to lead the market with 3 standard residential Low E double glazing options.  Since that time the range has evolved and grown with Metro also expanding into Triple Glazing.

The infographic below gives a snapshot of the various U Value performance levels, note Classic and Low E Plus in both Double and Triple glazing use an aluminium spacer and the argon gas.  All the other options include a warm edge/thermal spacer and argon gas for free.  When used in thermally broken frames options with warm edge/thermal spacer should only be used.  The options are ranked with the best performing at the bottom.

Note Grey, Green, and Bronze Tinted Double Glazing are not listed as the performance level for keeping a home warm is the same as Classic Double Glazing.

The industry measure for thermal insulation and keeping a home warm is called U value.  The lower the U Value the lower the heat transfer, the better the thermal insulation.

This comparison point in the infographic above is a 12mm spacer to suit most new NZ standard window frames. It should be noted that for Retrofit double glazing unit spacers will generally be narrower to fit the window frames, and thus have slightly lower thermal performance levels.

While Metro has spacer widths of 8 though to 18mm available.  The key driver of the double and or triple glazing thermal performance is the Low E glass selection.  E.g. a Low E Xcel Double Glazed Unit with a spacer of 16mm (unit 24mm) will achieve a U Value of 1.1.  Beating all but a triple glazed unit also of Low E Xcel makeup with spacers of 10mm (Unit 36mm) also achieving a U Value of 1.0.  Using 16mm spacers in the triple glazing would make a further jump in performance to a U Value of 0.90 but with a unit increase to 44mm.  Full technical tables for Double Glazing available here and for Triple Glazing here.



Large areas of clear glass are a wonderful way to create a bright, healthy home.  However, without the right glass selection in either double or triple glazing, the home can over-heat.  In fact, without some solar control selection double and or triple glazing can trap the heat gained through the day in the home.

Previously body tinted glass was used to reduce the amount of heat and light transfer, to help keep summer heat out and reduce glare.  With tints being on the outside piece of glass, the double glazing unit does heat up and needs to be heat-treated/toughened to avoid thermal breakage. 

As Low Double glazing will help keep a home warm in winter unlike a tint and cooler in summer, their use is becoming more common.  The type of Low E double glazing chosen also determines how much infrared light (radiant heat), visible light (glare) can be reduced.  Low E can let in more visible light to keep a home light and bright without the side effects of overheating.

When comparing double and triple glazing units against each other, it is important to compare the same measure.  There are three common measures used by the window and glass industry.  For all three measures the lower the number the better the window will be at reducing heat gain and keeping your home cooler.

  • SF = Solar Factor called g value in Europe (European EN Standard)
  • SC = Shading Coefficient (American NFRC Standard)
  • SHGC = Solar Heat Gain Coefficient (American NFRC Standard)

The infographic below gives a snapshot of the various performance levels available using Solar Factor (SF) ranked in order of performance across double and triple glazing with the best performing option at the bottom.


Large areas of clear glass are a wonderful way to create a bright, healthy home – light has been shown to reduce bacteria build-up in dust by half.

It’s so important that Natural Light has its own section in the New Zealand Building Code.  It sets out the minimum legal limits for homes including bedrooms, that should have at least 1 or more windows to let in natural light.

Along with natural light, large windows can also let in a lot of heat Glass naturally blocks UVB rays, and with the addition of a laminate it can block most of the UVA rays.  So, it is important to also consider solar control when looking at large glazed area particularly when north facing.

The infographic below gives a snapshot of the various performance levels, for both Double and Triple glazing.  The performance measure for natural light coming through the glass is called VLT – Visible Light Transfer.

Note triple glazing will let in less light for a comparative glass type due to the number of panes.  E.g. Classic Single Glazing has a VLT of 90% versus 82% for Double Glazing and 74% for Triple Glazing. 



Windows don’t create condensation, high moisture levels in the air combined with low internal temperatures are the cause.  High humidity not only increases the chance of condensation, but also the risk of airborne allergens such as mould or dust mites.  The ideal humidity range to avoid these issues in an average home is 40 to 60 percent RH.

Typically, modern homes with increased levels of insulation, better ventilation, and higher performing windows, have helped reduce most of the weeping windows evident in older single glazed homes. Higher performing glazing in homes works to form a thermal barrier to the outside.  Making the inner side of the window warmer, which helps prevent internal condensation.  Generally, the higher the thermal performance of the glazing the better it is at reducing the chance of condensation occurring.

It’s important to note that the average home releases around 8 litres of water a day into the air, from activities such as cooking, showering, clothes-drying, indoor plants etc. So, to help remove excess internal moisture, ventilation is important.


MBIE smarterhomes

Window and Glass Association Condensation Guide

The following infographic shows what the internal temperature of the glass would be when a home is heated to 200C inside and is 00C outside with the relative humidity 65% inside.  These factors can predict if condensation is likely to occur.  For the conditions shown the threshold for the internal glass surface temperature to have condensation form on it is under 140C.  Thus, ventilation is also a key as part of the mix for a healthy home.


The following infographic illustrates the differences if the outside temperature is 00C outside (top blue line) and -100C outside (bottom dashed blue line).  Condensation would still occur for both classic and double glazing at the 65% RH level.  Again, condensation would be likely to occur with internal glass temperatures under 140C.


While high-performing Low E double and Triple glazing will significantly reduce the likelihood of internal condensation. It is so efficient, morning dew can form on the outside glass surface, often seen as external condensation. When external temperatures are low and humidity levels are high with little breeze, this is when it is most likely to occur. Homes that have no eaves, are sheltered from prevailing breezes and high humidity/ cold conditions overnight, (normally experienced in Spring and Autumn) are more likely to see this occur. 

This is an indication of how well the double or triple glazing is working, and it will dissipate through the morning, given a breeze and or exposure to the sun.



Along with natural light large windows can also let in a lot of heat and UV rays that can be harmful to artwork, carpets, and furniture.  Glass naturally blocks UVB rays, and with the addition of a laminate it can block most of the UVA rays.  However, it is generally also important to consider the amount of visible light required in conjunction with fading reduction to get the right balance.

While body tinted glass works to reduce the amount of light transfer to reduce fading.  Low E double or triple glazing also helps reduce fading, with the added advantage of a warmer home in winter.

UV accounts for approximately 40% of the effects of Fading, thus the industry measure for fading reduction is a weighted measure called Tdw-ISO: The lower the Tdw-ISO the greater the reduction in fading by the glass.

Low E and Tint combined options are available; however, moving to a solar control Low E like Low Xtreme with a laminate will generally give a better all-round result.

Note with tints being on the outside piece of glass, the double glazing unit does heat up, and needs to be toughened to avoid the chance of thermal cracking.



If you live on a busy road, near train tracks or a school, or even if you have noisy, boisterous children of your own, you will know how disruptive excessive noise can be. Noise transmission through your windows can be reduced by mass: using thicker glass, a wider spacer between the glass and laminate, or a combination of the two. Laminates are used in most applications to avoid extra weight and thickness in the double and or triple glazing.  All of Metro’s laminates are also grade A safety glass so can fulfil a dual purpose of increasing safety and security while reducing noise transfer.

However, if noise reduction is a key issue, it’s best to engage an acoustics consultant to assess your home or new build.  They will make a recommendation for the key frequencies of the sound at your location. They can also assess the structural elements of your build to ensure they provide a complete solution. For example, the interaction of glass, joinery and the building envelope are key. For the best sound reduction, thermally broken frames are also recommended.




Safety around the home is of paramount importance, with safety glass required wherever there is risk of human impact – this is mandated by the NZ building code. There are two main options for safety glass - toughened and laminated. Toughened glass has undergone heat treatment and is ideal for safety, strength, and temperature resistance. If it is broken, it will break into small pieces, which reduces the risk of injury. Laminated glass incorporates an interlayer between two pieces of glass. It is much more difficult to break and if it does, the interlayer holds the glass fragments together.

Your Window and Door supplier will automatically supply safety glass for the areas of the home that are subject to Human Impact to meet the building code requirements.  These are areas such as doors, sliding doors and full height windows.  For double and triple glazing this may well be on the inside and outside pane



For security as laminated glass stays together it is much harder for an intruder to get through and break into the home. Useful for areas close to doors or latches to reduce the chance of burglars breaking the glass and entering your home. 


Privacy can be compromised by large expanses of glass. and this is especially true of urban areas where houses are close together. Fortunately, there are ways you can increase the amount of light coming into your home with increased glazing that is thermally efficient without sacrificing privacy. Patterned, obscured/frosted, tinted and reflective glass are all options for double glazing units. Digitally printed patterns are now also used, it’s even possible to print patterns or graduated frosting effects to let in light at the top while providing privacy at the bottom.

Patterned/Textured and obscured glass diffuse the light to reduce visibility through the glass while still allowing the same amount of light to transmit into the living space as standard glass.

Tinted glass works by reducing the amount of visible light both in and out of the home.  With tints being on the outside piece of glass, the double glazing unit does heat up, and needs to be toughened to avoid thermal cracking or breakage. Tints will also make the home darker

Reflective glass, typically seen in office buildings, provides a one-way mirror effect during the day. This blocks visibility externally in the day and internally at night. With the lights on at night you can clearly see into the home.



Architects and designers specify good insulation and design a house with cross ventilation that will help keep your home at a comfortable temperature on hot days.

But it’s useful to know the role windows play in achieving a comfortable home, especially in light of the trend for expansive areas of glazing to maximise natural light and views, not to mention the demand for extra-wide openings that allow an easy indoor-outdoor flow. Ideally, larger windows (and living areas) are on the east and north facing side of the home, with smaller windows to the west and south. This reduces the chance of overheating on the west side and reduces the impact of cold on the south side of the home in the winter months. It is worth considering moving living spaces to the north side if you are planning a renovation.

However, if your main views are to the south or west, you can override these design considerations with high-performance Low E double or triple glazing, in conjunction with thermally broken frames. Consider, also, windows above eye height. Clerestory windows let in light, yet still allow plenty of wall space and privacy. These windows are particularly useful for a south-facing house where they can let in light from the north (at the rear).

Skylights and roof windows are another way to bring in light.

For the past three decades there has been a trend towards houses with no Eaves. Yet eaves have real advantages. They provide shade when the sun is at its highest in summer, however sunlight can still come into your home in winter when you most need it. Eaves also help to reduce external dew (external condensation) forming on the outside of south facing windows, which is more evident with higher performing double and triple glazing.

With great insulation and efficient window frames, your double or triple glazing selection can provide performance beyond the minimum requirements of the NZ Building Code – for the life of your home. As New Zealand’s largest double and triple glazing producer, Metro Performance Glass can work with you and your window supplier to develop the best solution for your home, customised if necessary, to meet your needs.