Imagine spending thousands on high-performance, energy-saving windows — only to find they barely make a dent in your utility bills. Instead of a home that stays naturally cool in summer and warm in winter, you’re left with a big hole in your savings and a nagging sense of regret.
This happens more than you might think. But the windows themselves aren’t usually to blame.
They typically perform as advertised, increasing energy efficiency so you can shrink your utility costs and keep your home comfortable all year round.
So what is the problem? And how can you fix it?
To answer that, we have to understand that window manufacturers look at two key variables when assessing their product’s effectiveness: the Solar Heat Gain Coefficient (SHGC or g-value) and the U-value.
What Are Solar Heat Gain Coefficient (SHGC or g-value) and U-values?
The SHGC measures the amount of solar radiation that is transmitted through the glass.
The U-value, on the other hand, measures how quickly heat transmits through a material, its conductivity. The lower the U-value, the slower the transmission — and the lower your bills. For windows there are two U-values, one for the frame on it’s own and one for the glass on it’s own.
In Australia these are calculated together for a WERS certificate, which leads to a very inaccurate way to demonstrate actual window performance. However, this is the system we have, and one critical thing you can do as a homeowner, is understand the importance of getting the glass right, as that represents the largest surface area of a window.
So, to save money in the long run, you want low U-values and the right SHGC for the orientation of individual windows.
But Here’s the Thing
If you don’t install your high-performance windows properly, you’re essentially stripping them of their advertised U-value.
In other words, you’re taking away their capacity to keep your home comfortable — the capacity you paid for.
It would be like a bank installing a heavy-duty vault door on a flimsy gyprock wall. However, in our case, instead of bank robbers, the outside temperature is the thing we’re trying to keep out.
With that in mind, what might cause a window installation to go awry?
The #1 Mistake Homeowners (and Builders) Make
The main culprit here is improper sealing.
If your builder rushes the job, failing to fill in the gaps around the window frame, it can lead to a number of issues, including:
Energy loss. If you have gaps between your walls and window frames, it undermines your home’s thermal envelope. In summer, your house will absorb the sun’s heat like a sponge. In winter, it will quickly shed its warmth, replacing it with cold air from outside.
Mould growth. Improperly sealed windows allow the perfect conditions for a thermal bridge, where cold air from outside can come into contact with warm surfaces inside, resulting in condensation and mould. Beyond compromising the structural integrity of your home and making it smell bad, you could be exposing your family to serious health issues, such as respiratory problems.
Financial strain. If your house can’t regulate its temperature, carelessly exchanging heat with the outside environment, you’ll have to rely on your aircon or heater to stay comfortable — which means higher electricity bills. Add repair costs for water damage and mould to the equation, and it’s unlikely you’ll get the ROI you were hoping for when you ordered your windows.
The good news is it’s relatively easy to eliminate air gaps and get the comfort and energy efficiency you paid for.
How to Guarantee Energy Savings
When building or renovating your home, it’s important to speak with your builder about their window installation process before you commit to anything. With a good builder, the process will look something like this:
Step #1: During the design process, your builder will help you choose the windows that will best suit your home — not just the most expensive ones. For example, here at Enduro, we often recommend uPVC window frames, these eliminate thermal bridging at the frame and are a very cost effective option when compared with timber and semi-commercial aluminium frames you often see in luxury homes.
Step #2: Your builder will also help you choose the best positions for your windows. That way, you’re taking full advantage of natural light, which not only reduces the need for artificial lighting but also helps prevent mould.
Step #3: Your builder will create a model of your home using 3D tools so they can approach the construction process with unwavering precision. This ensures your windows fit snugly within your walls, eliminating any large air gaps.
Step #4: Your builder will then fill in any minor air gaps using specialist insulation and flashing tapes. The insulation seals off drafts, while the tape provides a weatherproof barrier around the frame, protecting your home from both air leaks and moisture.
Step #5: Before they finish up, your builder will test the integrity of each window for air tightness to ensure it meets the promised performance standards.
A builder like this may quote higher than the rest. But at the end of the day, spending a little extra now could save you big down the track — both financially and emotionally.
Bottom Line: A Quality Builder Can Save You Thousands
It doesn’t matter how much you spend on your windows; if they aren’t installed properly, you might as well have chosen a cheaper option.
By taking the time now to find the right builder — someone with a meticulous approach to window installation — you could end up saving thousands on utility bills each year.
More importantly, you’ll create a more comfortable and healthy living environment for you and your family.
But when it comes to building or renovating an energy-efficient home, proper window installation is just one piece of the puzzle.
That’s why we’ve put together this guide for you to download:
The 5 Key Skills of an Energy Efficient Builder
It’s filled with insights to help you avoid the construction pitfalls that catch far too many homeowners off guard.
