Episode 12

Low-E Glass, WERS and Glazing Optimisation, with Adam Winterbon of VENTORA Group

2 July 2026 · 43 minutes · Part 2 of 2 · Hosted by Brian Haines, Matthew Graham and Andrew Hooper

Summary

The second half of the conversation with Adam Winterbon moves from how windows are made to how they are specified — and to the gap between what an energy report asks for and what a window company can actually supply.

It opens with glass types and the practical consequence nobody warns you about: mixing different glasses across a facade can leave a finished house looking like a patchwork quilt, because reflectivity and tint differ even when the performance numbers work. Adam tells the story of a builder who ignored that advice and whose homeowners arrived at handover to find the sky reflected in two different shades of blue.

From there the discussion turns to WERS and WERSlink, AGWA's role as the industry's peak body, and the glazing optimisation study Matthew built with AGWA using two prototype homes Andrew designed — producing U-value and solar heat gain heat maps for every Australian capital city. It closes on window-to-floor area ratios and the cost cliff into thermally broken frames, the case for upgrading insulation before glass, and a case study where a five hundred dollar energy report saved a Queensland builder nineteen thousand dollars on windows.

In this episode

• 0:37Soft coat and hard coat Low-E (see corrections)

• 2:41Tints, clear Low-E and why some glass changes the look of a facade

• 3:37Reflectivity, and matching glass across a single elevation

• 4:54The patchwork quilt: a builder who did not take the advice

• 6:11Andrew's version of the same story, twenty years earlier

• 8:12What WERS and WERSlink actually are

• 9:29AGWA, and why Matthew joined it

• 12:02The glazing optimisation study, and the two prototype homes

• 13:12Heat maps of U-value against solar heat gain for every capital city

• 15:57Window-to-floor ratios, and the cost cliff into thermally broken

• 18:12Too much glass and too little: both are problems

• 19:29Insulation before glass: the upgrade order assessors skip

• 21:57Optimisation tools, and where simulation is heading

• 23:20The five hundred dollar report that saved nineteen thousand

• 25:30Why Queensland stayed on elemental reports, and what changed

• 34:04Imported windows, Australian standards and one certificate covering everything

• 39:00Should compliance certification be mandatory?

Key points

Performance numbers are not the whole specification

An energy report can arrive with different glass in different rooms, all of it defensible on paper. What the numbers do not capture is that glass types differ in tint and in reflectivity, so two products that both satisfy the calculation can look visibly different in the same room or across the same elevation. Adam's rule is straightforward: if you can see two windows at the same time, the glass should match.

The patchwork quilt

A builder within the VENTORA group was told this and proceeded anyway, on an energy report that had specified Low-E in some bedrooms, clear in wet areas and something else again elsewhere, purely to reach seven stars. The mismatch was invisible until installation. At handover the homeowners could see the sky reflected in two different shades of blue and the trees in two different shades of green. Adam describes it as a steep learning curve.

It has been happening for twenty years

Andrew tells a version from the FirstRate 3 and 4 era, when products were still rated under the older protocols and everyone was trying to match values across two different systems. A supplier delivered every French door tinted and every window clear, on the basis that the values matched the specification and nothing else was their concern. The client ended up applying film to the remaining windows, which changed the rating. His conclusion has not changed since: go through the windows one by one, and make sure the glass matches where it will be seen together.

What the AGWA study produced

Matthew ran the optimisation study for AGWA using two prototype homes Andrew designed — a single storey and a two storey — each modelled at a high and a low window-to-floor ratio. The output is a matrix of U-value against solar heat gain coefficient, rendered as a heat map for each capital city, so a designer can find the optimal combination for their climate at a glance. The striking thing is how different the shapes are between cities: some show a thin slither of viable options, others a broad plateau. It was distributed to AGWA members before the software tools were updated for NCC 2022, which for a period made it the only practical road map manufacturers had.

The ratios, and the cliff

The prototypes sit at 20.2 per cent and 27 per cent for the single storey, and 20.2 per cent and 28 per cent for the two storey — deliberately either side of the roughly 25 per cent rule of thumb, with the national average across the states at about 23 per cent, and aligned to the ratios used in the ABCB's own analysis. The practical warning is what happens past that: a five per cent increase in window-to-floor ratio can be enough to push a project from double glazed clear straight to thermally broken, with the cost jump and the site handling that come with it. Adam has builders at 36 to 38 per cent shipping fully thermally broken windows to Queensland to make it work.

Too little glass is also a failure

Builders in Victoria have tried 16 and 18 per cent to save money and found the opposite. A heating dominated dwelling needs enough glass to collect winter sun; take it away and there is nothing to collect.

Insulation first, glass last

The AGWA prototypes were deliberately well insulated — R6 to the ceiling, an R1.3 roof blanket, R2.7 perimeter edge batts, R2.7 walls, and R2.5 between conditioned and unconditioned spaces — because insulation is the cheapest way to buy stars. Adam still sees the reverse: high performance windows specified alongside R4 ceilings, R2 walls, and downlights that are not insulation contact rated, leaving holes in what insulation is there. When a report arrives with windows the manufacturer cannot economically supply, those are the first things he sends back to the builder.

The five hundred dollar report that saved nineteen thousand

A Queensland builder working through Stegbar was specifying double glazing throughout. VENTORA reviewed the energy report, asked whether the glazing could be scaled back and the insulation increased instead, and paid the five hundred dollars to have the report redone. The quote came back down from double glazed to single glazed and the builder saved nineteen thousand dollars on that job — and on every job after it. Adam is clear-eyed that this means selling less glass, and equally clear that it bought a relationship for life.

Why Queensland arrived late

Queensland ran on elemental Deemed-to-Satisfy reports for years, and under NCC 2019 an elemental report often beat a NatHERS assessment on insulation and glazing — almost always on a double storey. NCC 2022 flipped that, and NatHERS became the easier path. The legacy is that elemental reports still arrive, and roughly nine times in ten they carry a single U-value and solar heat gain for every window and door in the house, which is not how windows behave: awnings, sliders and sliding doors all seal differently and rate differently. Getting that changed has been a real piece of work.

The compliance gap on imported windows

Beyond energy performance, the concern Adam raises is safety — wind loading and performance under pressure, where a window that is not fit for purpose has consequences beyond a rating. He describes certificates that appear to demonstrate compliance with Australian standards until you look closely and find a single casement window tested, with the whole product range sold under that one certificate. The number of Chinese importers into Australia has gone from around twelve five years ago to well over two hundred and ten. His answer to whether compliance certification should be mandatory is yes, with the caveat that policing it may be too big a job for now.

Documents referenced

• WERSlinkThe window energy rating database referenced throughout — searchable by manufacturer and product.

• Australian Glass and Window AssociationIndustry peak body, and publisher of the glazing optimisation study discussed in this series.

• National Construction CodeAustralian Building Codes Board — the code itself, and the Housing Provisions referenced throughout.

Transcript

Lightly edited for readability. Hesitations and repetition have been removed and technical terms corrected; the substance is unchanged. Corrections to statements made on air are marked where they occur. Part 1 is Episode 11.

0:05I always get mixed up on them. Brian, do you care to weigh in on surface two and three? No, I am not going to weigh in on that at all. I tend to trust the experts. So going with what you say, Adam — with coatings we have soft coat and hard coat, and we also have low emissivity and high emissivity, and when you get to the argon ones you have warm edges. What does it all mean?

Correction

Andrew has since noted that he meantlow solar gain and high solar gainhere, not low and high emissivity. The two describe different properties: emissivity relates to radiant heat transfer, while solar gain relates to how much of the sun's energy the glass admits.

0:47Soft coat and hard coat work differently in a heating climate and a cooling climate. In a heating climate — Victoria, southern New South Wales — you want a soft coat. That only works if it has no air flow, so it has to be on the inside of an insulated glass unit. If you put a soft coat on a single piece of glass it will not do anything, because the airflow renders it inert. That is why hard coat is used for cooling climates, because it is predominantly single glazing.

Correction

Soft coat and hard coat are not heating and cooling products. They are two different methods of manufacturing Low-E coated glass, and either can be produced with properties suited to either climate.

Hard coat, or pyrolytic, Low-E is applied while the glass is still hot on the float line, which fuses the coating to the glass and makes it durable enough to be used on a single glazed pane.Soft coatLow-E is sputtered onto the glass after manufacture and generally both looks better and performs better.

The reason a soft coat cannot be used single glazed is not airflow. It is that the silver in the coating oxidises when exposed to air, which degrades it — so it has to be sealed inside an insulated glass unit. What makes a particular glass suitable for a heating or a cooling climate is its solar and thermal properties, and the surface it is placed on, rather than which of the two methods produced it.

1:26What are some examples in VENTORA's range? We imported a product from China which has a code, but is essentially the same as AS2 from Planibel, and there is also an Optitherm product which is the hard coat version. Planibel AS2 might be widely known in Australia as a soft coat. Lightbridge was another one supplied out of Viridian — we had a few issues with that product over time, so we tried to move away from it, towards something VENTORA Glass could supply themselves. Planibel G is the one in Queensland that is predominant, and Optitherm.

2:41With all the Low-E glasses you can get tint, depending on the percentage of the metallic coating. Some Planibel G and AS2, which are our good options, are clear — there is no discernible difference between clear glass and those Low-E glasses. The performance is not as high as some others, but it gives you the flexibility to put Low-E only where you need it. You can put it in the doors in your alfresco area and leave the rest of the house clear, and you will never see the difference. Whereas SolTech and Comfort Plus, the old Oceania products, performed better but had a brownish tinge, so you would not mix those in the same room with clear glass.

3:37There are benefits to both. If you need the performance you would do the entire room or the entire facade. They also have different reflectivity, so from the street, looking at the front of a house, you would want it all to look the same. You would not want Comfort Plus and then clear, because they look completely different when the sun hits them. Those are things we need to educate builders on when we are quoting and they have asked for different glass in different places — we need to tell them it looks different.

4:09It goes right back to the energy raters, because they probably started the problem. They came up with a solution of codes that got the project to six or seven stars, and it has a knock-on effect. It creates a difficulty for industry to provide a quote — the quote can be done, we can do anything you want, but you might not have windows that sit in that range. The U-value is out, or you are not within the plus or minus five per cent on the solar heat gain. And it does not flow back, it just flows down.

4:54There is a good example of a builder within the VENTORA group who did not take our advice. The energy rater was simply getting it to seven stars, so there were bedrooms with Low-E, wet areas with clear, and another room with something else. We knew none of the glasses matched and it would look different. They did not listen until the windows were installed and the homeowners went to take handover — and it looked like a patchwork quilt. You could physically see the sky in two different shades of blue and the trees in different shades of green. That was a steep learning curve. It is the sort of thing that is a challenge: we do not want to tell builders how to suck eggs, or tell engineers how to do their job, but we understand glass and we understand windows.

5:54I do not think it is telling them how to do their job. I think it is just education — raising awareness about taking that little bit of extra care.

6:11I will tell a tale from many years back, in the early days of FirstRate 3 or 4, when products were still being produced under the older protocols rather than the AFRC ones. We had a Low-E window at a particular set of values, and it came across tinted, but everyone was trying to match it against current values which were AFRC. There was a window company — I do not think they are around now — who were just a supplier. They would source products and dump them on the customer. The client rang me and said they had produced all these windows at that value, and every French door, and there were about twenty of them, was tinted. Every window set was clear. The window company said they did not care, that matched the values, that was all they were worried about.

7:18From that moment it always taught me: go through the windows, and certainly with a custom job, make sure the glass matches where you want it to match. If it is in the same room, if you can see two windows at the same time, always ensure the glass is exactly the same. You learn the hard way and you get upset clients. There was no recourse that I am aware of — I think she ended up tinting the other windows with film. And of course once the tinting went on the rating drops, because it was a Melbourne job. Everything snowballs, just because of the way it looked.

8:12We have thrown around a few acronyms tonight, one of them being WERS and WERSlink. WERS is the Window Energy Rating Scheme, and WERSlink is the online database. It is public facing, so anybody can go in and search and browse through filters and find all of the WERS rated windows. It is kept up to date, all of the windows on there have AFRC certified U-values and solar heat gain coefficients, and it connects almost live into the NatHERS software tools for assessors to use — depending on which software you use.

9:23The other acronym is AGWA, the Australian Glass and Window Association: the national peak body representing window manufacturers and glass and glazing manufacturers.

9:52I became an AGWA member a few years ago and I have really enjoyed working with them. The catalyst was simply to understand more about the window industry. I realised I did not know as much as I thought I knew about windows. I have been fairly lucky in that people like Dr Peter Lyons have helped me understand them over the years — without his guidance I do not think I would have got my head around it — but something still seemed to be missing.

10:48I became conscious that window manufacturers were struggling with a lot of the NatHERS certificates they were seeing: the fifty-seven varieties of window on one job, or the single window code for a whole house. I needed to understand what the issues were for the window industry, so I could take that back into my own industry and raise awareness. A few years later I am still going to the Melbourne member meetings, and I was invited as a guest speaker to OzFenex last year where I gave two talks. It is a great community. You would think there would be a lot of rivalry, and there is a little, but there is also a lot of camaraderie as they work towards a common goal.

12:02One of the first projects we started was looking at optimising windows for seven star energy efficiency. It was published around 2023 or 2024 — I started in 2022 — and was initially made available to all AGWA members in printed format. It looked at two housing prototypes: a single storey project called AGWA 1 and a two storey project called AGWA 2. And who put those together? Well, that is a leading question. Andrew and I worked on it — Andrew came up with the designs, and they have two different glass to floor ratios, a high one and a low one.

13:12What we did was run a lot of simulations to produce a matrix of U-values along one axis and solar heat gain coefficient along the other, to come up with a heat map for each of the capital cities around Australia. It works as a ready reckoner: you go and find where the optimal U-value and solar heat gain sit for your climate zone, where that sweet spot is. What is fascinating, and I suggest people download some of these from the AGWA website, is that the shapes are really different. Some have thin slithers, others are really broad, some have a lot of depth in them. It reflects the diversity of the Australian climate zones.

14:28The book was critical for us in the early stages. It came out before NCC went live and around the same time as, if not before, the software packages were updated. Until we could put a significant number of live jobs through the software, we did not have much understanding of where we needed to be. So the book drove our road map — making sure we had performance in the sweet spots for each climate zone. When NCC went live and everybody was asking, we had our good, better and best options ready. We were not playing catch up, which was fantastic.

15:35Once the energy reports came through we got differing information, a lot of it down to builders' inclusions on different house lots. They were not exactly what AGWA 1 and AGWA 2 had as baseline inclusions for insulation and flooring, and some of our builders are well outside the sweet spot on glass to floor area ratio.

16:09The ratios: AGWA 1 at 20.2 per cent for the low and 27 per cent for the high, and AGWA 2 at 20.2 and 28. So either side of the rule of thumb that sits around 25 per cent for glass to floor ratio. We looked at the average window to floor ratio across all the states, which is 23 per cent, and aligned the ratios with the ABCB's own analysis, so there was method in the madness.

16:45It is not too dissimilar to a normal volume build design. But when you get anything remotely custom designed with a high window to floor area ratio, it falls off a cliff instantaneously. You go from double glazed clear to thermally broken purely because your ratio has gone up by five per cent. That is not much, but it makes a massive difference in cost and specification, and then you are looking at crane lifts on site and more people to manoeuvre the windows. It is a domino effect.

17:36It is critical for us, and it is difficult to tell builders they have too much glass. They do not want to hear that they have a 36 per cent window to floor ratio and that is why they cannot get windows to meet seven stars.

18:12But you can be too low as well. In Victoria we have had builders trying to do 16 and 18 per cent to save money, and unfortunately you need some glass area to get sun, especially in winter, and draw in as much heat as you can. If you have no windows you cannot do that. So builders have gone both ways and it is something we manage with expectations. Some of those builders at 36 and 38 per cent building in Queensland are shipping fully thermally broken windows up there to get the specification their homeowners are after — and there is a big cost in that shipping. At that end of the market, homeowners tend not to baulk at the price. If it is their once in a lifetime dream build and they can afford it, they will do what they can.

19:29One of the things in the study was to put the emphasis on the windows only after optimising the insulation. AGWA 1 and AGWA 2 had R6 in the ceiling, an R1.3 roof blanket, R2.7 perimeter edge batts, R2.7 in the walls and R2.5 between conditioned and unconditioned spaces — fairly highly insulated buildings. Where are we going wrong?

20:03I do not think you were going wrong anywhere. The logical thing is to upgrade insulation first. That should be in any energy rater's upgrade hierarchy — insulation upgraded first, because it is the cheapest way of increasing the star value, then move on to window specification.

20:28Have you seen energy raters with low insulation and a high window specification? It does not seem logical. No, it does not, and we have definitely seen it. High performance windows, and then I check the rest of the report and there is R4 ceiling insulation, only R2 in the walls, and some people still not using insulation contact rated downlights, so there are holes in the ceiling insulation. When they are struggling to get windows that perform and meet compliance, those are the things I go back to the builder with. Sometimes there are valid building practices behind only using R4 in the ceilings. Other times they can make changes and accommodate — it is just that nobody has ever told them.

21:16Our initial assessment was that it makes sense to upgrade all the other building elements as far as you can before touching the glazing, because they are cheaper alternatives. Not that we want to take away from window performance, but if we are talking about changing frames and weights and potentially glass colouration, you want to stick to the lowest specification windows you can for those project home builders. So there are energy reports we are still seeing that are not as optimised as we thought they would be.

21:57There is the word optimisation, which is a timely reminder to give a shout out to Nick Bishop and the HERO Software team. This study would not have been possible without their help. It was bleeding edge and required modifications to get the work done in conjunction with AGWA. Fast forward to 2026 and, depending on which NatHERS tool you use, optimisation functionality has been there for a while — and we are on the precipice of a new release which will bring even more powerful optimisation. So there is no excuse for energy raters not to roll up their sleeves and run more automated simulations to test the U-value and solar heat gain and find that sweet spot, the same way I did a few years ago with this study.

23:20What we have offered builders in the past is: you have your energy rating as it is now and we can quote on that, but if you are able to bring the window specification down we will requote your windows at the lower specification and show you how much you can save. Then you go back to your insulation people and say we are now going from R4 to R6, and we are upping the walls, and we are putting bigger waffle pods in. If you do that it might cost an extra fifteen hundred, but you save three or four thousand on the windows. You are ahead by two thousand, and it cost an extra five hundred for an energy report.

24:22Why do you think that does not happen more? I think the issue is that the energy rater simply does not know who the window manufacturer is. If you are working for a volume builder doing hundreds a year, you know the codes and what they will specify, and the job goes straight to the manufacturer. But if you get a one-off, or a builder doing ten a year shopping between three or four manufacturers, you do not know what specification to put in. You can use defaults, or what you think it is going to be. But if they go to a manufacturer and it cannot be quoted, they should come back to you to reorder things and change the codes to match — and I just do not think that back and forth happens.

25:30One of the issues in Queensland may be the deep-seated elemental Deemed-to-Satisfy energy reports that have been going on there for a decade and a bit. NatHERS assessments are taking over and are relatively new, so maybe there is a lack of understanding of how to do an efficient assessment. The other states have been doing NatHERS reports for decades.

26:20We found that when we did our large voice of customer piece before NCC 2022. We got reasonable buy-in from Victoria — I did eighty or ninety customer visits talking about energy ratings. But when we reached out to customers in Queensland they were very laid back: we will worry about that later, we are busy with other things. We even had builders ring us the day NCC 2022 went live saying maybe we should talk about energy ratings now.

27:26If you compared a Deemed-to-Satisfy report with a NatHERS assessment under NCC 2019, in about eighty per cent of cases the elemental report would win out on insulation levels and glazing specification — and pretty much one hundred per cent of the time on a double storey. Moving to NCC 2022 flipped it the other way, so NatHERS has become the standard. But not everybody has that information, so we still see a lot of Deemed-to-Satisfy reports coming through, and ninety per cent of the time the windows and doors all carry the same U-value and solar heat gain, which we know is not the case. For us to do our job properly and give a quote with one type of glass — awning windows have to have different ratings to sliding windows and sliding doors, they all seal differently and perform differently. Explaining that to a builder, and getting the people doing those reports to change, has been a real challenge.

33:59How important is AGWA in standardising the industry? We have a very high opinion of them. They are our industry body, we attend all their events, and all our brands have been members a very long time. There are issues they get into with non-members where they have no standing, and sometimes builders do not care about AGWA's opinion, but they are very good at dealing with members and making sure the right things are done for the industry.

34:52I personally feel it is important to have a level playing field. With windows being imported from Europe and Asia, more than ever windows should be rated to a certain standard and be ratified and available, so that energy raters, architects, building designers and homeowners can understand the performance difference and make an informed decision. I do not think it is good enough to say the windows perform like this and just trust us because they have been assessed in whatever system their country uses. We have a standard here in Australia, in the National Construction Code. I understand they do not have to be in WERS, but it is important to have a benchmark.

36:11You are absolutely right, and for energy that is the case — but it is even more important for all the other Australian standards that some overseas suppliers do not necessarily meet. Wind loads, performance under pressure, those are genuine safety issues if windows are not fit for purpose. There have been instances where windows have failed and people have been injured or killed. That is worst case, and something we need to stamp out. AGWA makes sure all their members are compliant and audits them every year, which is great — but the level playing field does not exist at the moment, and it should.

37:26At the AGWA members meeting a couple of weeks ago, some overseas imported products out of China had certification saying they met Australian standards. On face value they looked absolutely fine, but when AGWA dove deeper into the reports they pulled, there were glaring inconsistencies, which were concerning at least. With an Australian standard and an AGWA member you know what you are going to get and it is all legitimate. We are not entirely sure that is the case otherwise, and it is extremely difficult to prove. So it is buyer beware, though in a lot of instances it is far too attractive to pass up.

39:00Does the government need to enforce more on imported products? If you buy an air conditioner it has to be rated. If you use a cladding product it has to be code marked. Should it be mandatory to carry an exact demonstration of compliance to standards? Yes is the short answer, though there is more to it. When you dive into some of these compliance certificates, they say all of their products in a house have been deemed compliant and tested, but when you look into it they might only have one casement window that passed certification and they are selling all of their products under that one certificate. Five years ago there were about twelve Chinese importers into Australia. Now there are well over two hundred and ten. It has absolutely blown up in the last few years. There is work happening at government level on stopping the flood of imports below Australian cost, but on the compliance side it might just be too big a beast for right now.

41:11Thanks for joining us tonight, Adam. The conversation has been amazing and we all learned so much. Thank you for having me — I could talk windows for days. That wraps up this episode of The Rating Room. Thanks for joining myself, Matthew, Andrew and Adam as we uncovered another corner of the NatHERS world. Your thoughts, comments and questions are important to us, so leave a message on the NatHERS Assessor Network Facebook page or leave a comment below. Until next time, keep rating.