7 min readApr 27, 2022


Sharing our insights into the biggest sustainability challenges facing our built environment. We continue the series by looking at the impact of a seemingly benign topic: windows.

Photo credit: Kenrick Baksh

In our last issue of the UNSUSTAINABLE series, we talked about the environmental cost of cooling and the urgent need to find sustainable solutions. Digging deeper into the biggest sustainability challenges facing our built environment led us to another massive issue no one is talking about: Windows.

The Problem

The typical home gains 25–30% of its heat in the summer and loses 25–30% of its heat in the winter through windows and doors, presenting huge inefficiencies in current building design. This figure can rise to 40% in older single-glazed buildings which means a staggering 40% of the heating and cooling energy demand is coming directly as a result of windows.

Although many improvements in glass technology have been made over the years, including double-glazing, adoption of these is limited to just 18% in global residential buildings and just 6% in non-OECD commercial buildings worldwide.

The prevalence of single pane windows is surprising, even in developed markets such as the US where there is over 15bn sqft of single pane glazing and heat lost via windows costs $40bn annually, accounting for 13% of the building sector’s emissions. In the summer, ~6% of all the electricity produced in the US is used to run air conditioning, at a cost of $29bn annually.

Europe isn’t much better, where 44% of the glazing distribution is single glazed.

Source: Glass for Europe/IEA workshop (2011)

Although insulation and cavity walls can be created to insulate walls against heat loss, this solution cannot be extended to windows without blocking light or views. The thermal image below demonstrates the heat loss through windows in a home:

Source: Infraspection Institute

Energy Efficient Windows

To reduce the effects of outdoor weather conditions on an building’s internal environment, a number of technologies have emerged as energy efficient solutions:

Double/Triple Glazing

Following the introduction of building regulations to improve energy efficiency in the early 2000s, double glazed windows became popular and now make up 80% of the new window market today. Efficiency gains are around 30% compared to single glazed windows, with argon gas between glass panes providing some thermal insulation. Nevertheless, without low-e coatings, these windows mainly reduce heat loss and do not reduce solar heat gain from direct sunlight coming through the window.

The following photo shows a building with double glazed windows on a summer’s day in Battery Park, New York where sunlight is causing significant internal heat gain through the windows.

However, by introducing triple glazing and low-e coatings, the improvements are immense. Here’s a photo of the Freedom Tower in New York, a mostly glass façade, which stays cool despite the massive heat gain suffered by adjacent buildings with far smaller window-to-wall ratios:

Smart Windows

Smart window technologies emerged to allow dynamic regulation of light and heat without compromising the visibility or views of a user. Current smart window technology can improve building performance via thermal management, daylight regulation, and reduction of glare while maintaining views. New research is being done to implement power capture and even information displays in smart windows.

The most common smart windows are thermochromic, where a chemical is activated when the glass heats up with the sun, limiting the solar heat that can penetrate the glass:

This kind of solution is useful even at temperatures below zero because on a clear day, the sun can still cause a building to heat up (greenhouse effect). The heat gain inside the building means that the air conditioning has to work harder (which increases energy usage) to keep the building cool.

An electrochromic smart window is modulated by changes in the voltage applied to the material between the glass (pictured below). Applying low voltage darkens the coating between the panes creating the appearance of colour, whereas removing voltage causes the glass to lighten and return to transparency. The change in colour reduces the solar radiation (heat and light) and solar glare emitted through the second pane of glass.

Source: Brzezicki (2021): A Systematic Review of the Most Recent Concepts in Smart Windows Technologies with a Focus on Electrochromics


Despite advanced energy efficiencies compared to static windows, smart windows have not yet achieved a significant level of market penetration. Window manufacturing is consolidated and capital intensive, it can be challenging for new entrants to compete with incumbents’ scale.

The main barriers to smart window adoption are:

  • Optical performance: Low optical contrast and long response time. Long switching times can create user discomfort and glare
  • Colour suitability: Blue and brown light materials influence the colour perception in the room
  • Suitability for hot climates: Tungsten oxide can cause glass to overheat to the point where it’s too hot to touch
  • Cost: Smart window solutions are typically between 2–10x the cost of traditional windows
  • Lack of industry standards: There are currently no unified industry standards to compare different technologies, which limits the accuracy of comparisons.


The global architectural glass market is valued at USD 115bn today and is growing at a compounded annual growth rate (CAGR) of 5.2%. In modern commercial buildings, window-to-wall ratios are often as high as 75% increasing global demand and production volume of architectural glass. Market growth is being driven by high demand for commercial floor space in the US (which is expected to grow by 33% between 2020–2050) and high rates of residential construction in the Global South (Mordor Intelligence).

As a small (but growing) sub-sector of the architectural glass market, the global smart glass market was valued at USD 4.7bn in 2020 and is expected to reach USD 7.5 billion by 2028 (CAGR of 6.8%). Growing demand across the transportation and architectural sectors is expected to fuel the market growth over the forecast period, as well as changing regulations e.g. the Green Building initiative by the European Union and the Building Energy Conservation Act. In New York City, a mandate for 40% emission reductions from buildings by 2030 has caused 10x growth in smart window adoption to meet the new requirements (estimate from Miru Smart).

Smart window market growth has also been fuelled by demand from electric vehicle manufacturers — electrochromic windows can increase battery range by 10–20%.

As we have mapped out the businesses innovating across the windows space we have come across some fantastic companies. Here are just a few of the players operating in the smart window market currently:

Our 2150 take

After our time digging into the world of windows we concluded that in order to reduce the energy consumption of buildings and associated CO2 impacts, action must be taken against both existing inefficient window design and future inefficient window installation. This involves finding easily retrofitted solutions such as low-e or UV/infra-red reducing films or spray-on coatings to reduce solar heat gain. Smart window companies need to focus their attention on materials, production processes, and ease of installation to provide solutions to the cost challenges before they can be scaled.

The impact potential from better windows is staggering; if high-performance windows are installed at a 2.75–5% annual retrofit rate, the emissions reduction could reach 10–12.6 gigatons of CO2e over the next 30 years! (source: drawdown.org)

From a venture capital perspective, that means we could definitely see Gigacorns emerging in this space in the coming years. Here at 2150, we’re still on the lookout for impactful companies tackling the window problem so if you’re building something exciting in this space, we can’t wait to hear from you!


2150 is a venture capital firm investing in technology companies that seek to sustainably reimagine and reshape the urban environment. 2150’s investment thesis focuses on major unsolved problems across what it calls the ‘Urban Stack’, which comprises every element of the built environment, from the way our cities are designed, constructed and powered, to the way people live, work and are cared for. Find out more at www.2150.vc




2150 is a venture capital firm investing in technology companies that seek to sustainably reimagine and reshape the urban environment.