The UK Green Building Council (UKGBC) added an insulating window coating for retrofit to its solutions resource in October 2023, under the date "Oct, 2023"1. The entry describes the product as an "Energy-saving alternative to window replacement"1.
The coating is a low emissivity coating applied to existing glass, and the resource states it can be applied to any window type, shape or style1. UKGBC says the technology is similar to a low-e coating but can be retrofitted rather than applied during glazing manufacture, and that it performs better than some factory applied coatings1. The page states that retrofitting with this coating rather than a low-e film is twice as durable, does not contribute to fire risk, and can be applied seamlessly1.
Figures on performance are given as information supplied by Window Insulation, the company named on the page1. Testing by Nottingham Trent University is said to have proved a reduction in U-value of 1.09W/m2K, from 2.63W/m2k to 1.54W/m2k, with the solution most effective on lower performance windows1. A study at Liverpool John Moores University is said to show a modern window improving from 1.2 W/m²K to 1.1 W/m²K1. The page also lists a 20-40% thermal resistance improvement, blocking of 99% of ultraviolet and 83% of infrared light, a 50% reduction in condensation, minimal impact on visible light transmission, and a reduction in overheating1.
| Measure | Figure given |
|---|---|
| Reduction in U-value | 1.09 W/m2K |
| Return on investment | 1-2 yrs |
| Warranty | 10 yr |
| Typical heating/cooling cost savings | 20-30% |
The page states that about 30% of a home's energy is lost through windows, citing the US Department of Energy, and that fully replacing windows can be expensive with high embodied carbon1. It notes the solution reduces g-factor from approximately 0.85 to 0.68 for a single glaze window, and therefore solar gains in winter, but says it significantly increases retention of paid heat1. UKGBC states the coating is proven maintenance free for 20 years and causes no significant change to window appearance, and that it has been installed in over 37 countries over the past 20 years1. The page carries a note that data, evidence and solutions are provided by partners and members and should not be attributed to UKGBC, and that UKGBC does not offer commercial endorsement of individual solutions1.
"This page presents data, evidence, and solutions that are provided by our partners and members and should therefore not be attributed to UKGBC."
Why it matters for households
Windows are one of the routes by which paid-for heat leaves a home, and the resource puts the share of a home's energy lost through windows at about 30%1. For a household weighing up insulation and glazing work, a coating applied to existing glass sits alongside replacement as an option that does not involve new frames or units, and the page states UK availability is "Yes"1. The claimed U-value improvements matter because a lower U-value means less heat escapes through the glass for each degree of difference between inside and outside; the figures given range from a large improvement on poor-performing windows to a small one on a modern window1. The reduction in g-factor means less winter solar gain, which the page sets against what it describes as significantly increased retention of paid heat1. Condensation and mould are also addressed, with a stated 50% reduction in condensation1. The page does not report an installed cost in pounds, so the payback figure of one to two years cannot be checked against a price here1. Households considering work of this kind alongside internal wall insulation may also need to deal with the window reveal, a separate detail from the glass itself.
What happens next
No next steps are dated on the page beyond the October 2023 addition1.