If you've been shopping for new windows or double glazing in New Zealand, you've probably come across the term low-E glass. It sounds technical, but the idea is straightforward — and for many Kiwi homeowners, it can make a real difference to comfort and energy bills.
What Does Low-E Mean?
Low-E stands for low emissivity. Emissivity refers to how readily a surface radiates heat. Standard glass has relatively high emissivity, meaning it lets heat pass through easily — great in summer if you want to lose heat, but a problem in winter when you want to keep it in.
Low-E glass has an ultra-thin metallic coating (usually silver-based) applied to one surface. This coating reflects long-wave infrared radiation — the kind your heater produces — back into the room, while still allowing visible light to pass through. The result is a window that feels warmer to sit near in winter and helps keep your home cooler in summer.
How Is It Different from Standard Double Glazing?
Double glazing alone is a big improvement over single glazing because the air (or gas) gap between the two panes slows heat transfer. Low-E takes this further by reducing radiant heat loss, which accounts for a significant portion of heat movement through glass.
| Feature | Single Glazing | Standard Double Glazing | Low-E Double Glazing |
|---|---|---|---|
| Insulation (R-value) | Low | Moderate | Higher |
| Radiant heat control | None | Minimal | Good |
| UV protection | None | Some | Good–Excellent |
| Condensation reduction | None | Moderate | Better |
| Relative cost | Lowest | Moderate | Higher |
Many low-E units are also filled with argon gas between the panes, which further reduces heat transfer compared to air-filled units.
Types of Low-E Coatings
There are two main types you'll encounter:
Hard-coat (pyrolytic) low-E
Applied during glass manufacture while the glass is still hot. It's more durable and can be used in single-glazed applications, but is generally less effective than soft-coat.
Soft-coat (sputtered) low-E
Applied after manufacture in a vacuum chamber. It performs better thermally but must be sealed inside a double-glazed unit to protect the coating. This is the most common type used in NZ residential double glazing.
When getting quotes, ask your glazier which type they're supplying and where the coating is positioned — the placement affects whether the glass is optimised for keeping heat in (better for colder NZ climates) or keeping heat out (useful in warmer northern regions).
Is Low-E Glass Required by the NZ Building Code?
The NZ Building Code sets minimum thermal performance requirements for windows through NZS 4218 and the energy efficiency provisions (Clause H1). Requirements vary by climate zone — homes in colder zones like Otago, Southland, and the central North Island face stricter standards.
For new builds and major alterations, your windows may need to meet a minimum window R-value that standard double glazing alone might not achieve in colder zones. Low-E glass can help meet or exceed these requirements. Always check with your glazier or building consent authority about what applies to your specific project.
BRANZ has useful research on window performance and thermal comfort in NZ homes if you want to dig into the detail.
The Benefits for NZ Homeowners
- Warmer in winter — less radiant heat escapes through the glass, so rooms feel more comfortable
- Cooler in summer — depending on coating type, solar heat gain can be reduced
- Less condensation — the inner pane stays warmer, reducing moisture build-up that can lead to mould
- UV protection — low-E coatings block a significant portion of UV rays, helping protect furnishings, flooring, and artwork from fading
- Lower energy bills — reduced reliance on heating and cooling, though actual savings depend on your home, location, and habits
- Healthy Homes compliance — for rental properties, improved insulation and reduced condensation can support compliance with Healthy Homes Standards
What Does Low-E Glass Cost in NZ?
Prices vary depending on window size, frame type, supplier, and region. As a very rough guide, upgrading from standard double glazing to low-E double glazing typically adds a moderate premium per window — often somewhere in the range of 10–25% more than standard double glazing, though this varies widely. Get at least two or three quotes from local glaziers to understand what's realistic for your project.
You can find qualified glaziers in your area through tradedirectory.co.nz.
Is It Worth It?
For most NZ homeowners — particularly those in the South Island, Wellington, or elevated central North Island areas — yes, low-E glass is generally worth the extra investment. The combination of improved comfort, reduced condensation, UV protection, and lower heating costs makes it a sound long-term choice.
In warmer northern regions like Auckland and Northland, the benefits are still real (especially UV protection and summer cooling), though the payback period on energy savings may be longer.
If you're already investing in new windows or retrofitting double glazing, the incremental cost of upgrading to low-E is relatively small compared to the total job cost — making it a sensible upgrade to consider.
When to Call a Professional
Window installation and glazing work should always be carried out by a qualified glazier. In New Zealand, window installation in new builds or significant alterations is often restricted building work under the Building Act, meaning it must be done by a Licensed Building Practitioner (LBP). Even for replacement glazing, a professional glazier will ensure correct installation, proper sealing, and that the unit meets Building Code requirements.
Never attempt to cut or handle large panes of glass yourself — glass injuries can be severe. Always engage a qualified tradesperson for glazing work.