In my previous post, I discussed IGUs and VIGs, and I recently stumbled across Scott James Windows in London while doing some research for my new book about historic windows and energy efficiency. They shared unique insights on the latest trends in the sash window double glazing niche in London.
I think it is quite interesting to see that is happening there as it might as well be an emerging trend here in US.
What’s Happening with Sash Window Double Glazing in London?
There are a few different approaches people take to insulate their homes when it comes to sash window double glazing.
The main options include:
- Plastic double-glazed windows – (a definite nope for me)
- New wood windows – (at lead they swap wood for wood, but still a hard no)
- Retrofitting original sash windows with slimline IGU or VIG units – (best balance to save history and achieve better efficiency
At Scott James Windows, they exclusively work with VIG glass because IGUs are not durable enough to justify the process which I whole heartedly agree with.
Market challenges
While restoration and draught-proofing remain popular, more homeowners are also opting for window reglazing or replacing the glass—though it’s still a niche market, largely because many people aren’t even aware that retrofitting existing sashes is an option.
Even those who have heard about it may still recall bad experiences with earlier slimline double-glazing units (reduced-depth IGUs) or outdated VIG glazing with visible evacuation ports in the corners. What I didn’t realize is how far the technology has come!
Today’s VIG glass no longer has visible evacuation ports, and with multiple manufacturers now producing it, prices are slowly coming down. Scott James Windows introduced me to Vitro Glazing which is just one of the companies that makes these new port-less VIG units. These truly are a gam-changer in my view because for the first time we can keep the historic sash and not compromise on appearance to achieve industry leading efficiency with the glass.
That said, window restoration specialists still face challenges in getting homeowners to see reglazing as a viable alternative to full window replacement.
Another interesting insight from my UK colleagues is how regulations affect decision-making. For Grade I and II listed properties, homeowners need permission to replace windows, which is why reglazing is widely accepted. But outside of the listed property market, many homeowners don’t realize reglazing is an option. Instead, they replace their sash windows entirely—sometimes with plastic frames, which is the worst-case scenario from both a preservation and aesthetic standpoint. Replacing your old-growth wood windows with vinyl is akin to all the bad decisions you made in college after a late night of drinking. Full of regrets and what was I thinking moments.
From what I’ve heard, raising awareness about reglazing could make a big difference in helping homeowners maintain the character of their properties while also improving insulation and energy efficiency.
Will VIG Help Restorers Compete with New Windows?
Looking at the benefits of VIG glass, such as efficiency and durability, and considering what’s happening in the London market, it seems that VIG could be a real ally for restorers. It allows them to compete with companies producing new windows because the best double-glazing units money can buy no longer have to be very thick or have triple panes.
With some reinforcement and weight adjustments, original frames can support heavier glazing, making the process straightforward. Finally, new technologies are here to help preserve more historic windows rather than replace them.
What Are the Challenges of Working with VIG Glass?
That was one of my questions to Alex, and here’s what he had to say:
“It’s a great product, but like anything in this world, there are pros and cons. The pros are well known, but the challenges mostly affect the installers.“
”The first issue is lead time. If you want to work exclusively with VIG, you need to have bookings well in advance. This means customers often have to wait 3 to 9 months to have their windows restored and reglazed. That’s a dealbreaker for some, especially developers who need a quick turnaround on their investments.”
From my experience running a window restoration company I can tell you that long lead time are pretty realistic just due to a backlog of work so perhaps if we order the glass at the outset then by the time we get around to commencement we will have the glass on hand.
According to Alex, “Another major factor is planning permission for historic windows. If we’re working on a listed property, the process can take years from the initial inquiry to the day we actually get the window in our hands. It’s a slow-moving process and one of the biggest hurdles for restoration projects.” Thanks government for making everything so much easier!
“It’s not an easy business to get up and running, but if you’ve been in the market for a while and know what you’re doing, it’s incredibly satisfying. Seeing an old window restored to be just as efficient as a new one—while preserving its history—is what makes all the challenges worth it.”
I couldn’t agree more with that last statement. I, for one, am incredibly excited that the technology of VIGs has moved forward enough that the aesthetics now match their amazing performance. That makes being a window restorer so much easier!
Founder & Editor-in-Chief
I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.