Building Envelopes

Proper building design, integrating high-performing envelopes, is the most effective way to reduce the thermal needs of buildings and deliver occupants’ thermal comfort. Compared to other solutions in buildings, the selection of envelope structure and materials is particularly important, given the long lifetime of buildings and the associated cost of the envelope.

In the last decade more widespread and stringent building codes, as well as increased retrofit rates, have helped decrease space heating intensity by 10% on average globally. Efficiency gains have decreased global space heating service demand by about 5% in advanced economies since 2010, but were not enough to offset floor area growth in emerging and developing economies.

Global space cooling service demand has increased in both advanced and emerging economies, up by about more than one-third since 2010, driven by increased floor area, equipment ownership and rising temperatures, but also by the fact the cooling-oriented envelope solutions are often neglected during building design.

Building envelope performance improvements are critical to getting on track with the majority of the Net Zero Scenario milestones in heating and cooling intensity (energy use per total m²). To align with the Net Zero Scenario, the final energy intensity of space heating and cooling need to fall considerably, by at least 40% and 30% respectively in 2030 compared to today. Progress in space cooling efficiency (from both improved envelope performance and air-conditioning equipment) is particularly needed due to growing demand.

Although all countries will need to implement mandatory building energy codes within the next decade to align with Net Zero Scenario milestones, many have still to make them an explicit policy priority.

Constructed floor space worldwide has increased by about 60% since 2000, to reach about 240 billion m² in 2021, of which nearly 80% is residential. At the same time, however, average energy use per m² has declined by only around 20%, meaning advances in energy efficiency have only partially offset floor area growth.

In addition to the lack of building energy codes in certain countries, the average retrofit rate of the building stock is currently around 1% per year, with retrofits generally delivering average energy intensity reductions of less than 15%. To get on track with the Net Zero Scenario, however, retrofit rates must jump to at least 2.5% by 2030, and retrofits need to be deep retrofits.

By 2030 all new buildings and retrofits are zero-carbon-ready buildings under the Net Zero Scenario.2

Building envelope solutions are well known, such as energy-efficient insulation and fenestration. But innovation is also taking place in building envelope materials and components, for instance to reduce the thickness of insulation, resulting in a product five times more efficient than traditional insulation. Use of super insulating materials, e.g. vacuum insulation panels and silica aerogel, can offer additional economic benefits by creating additional usable space and hence increasing the financial value of the building. This solution is particularly interesting for areas that previously would have remained uninsulated due to insufficient space.

Ongoing research is taking place in the area of supercool and smart materials, which can stay several degrees cooler than ambient temperature even in direct sunlight and thereby reduce cooling needs inside the building, with particularly promising results in hot and dry climates.

Adaptive building envelope systems, including control and automation technology, are on the rise. Among the building envelope technologies that enhance the envelope’s function through solar energy gains, “climate-adaptative building shells” offer the opportunity to activate buildings against climate change. The façade's adaptation to climate conditions creates changes in the building's energy balance through convection flow, radiation and energy storage.

Building renovation is often intense, not only requiring significant skills to select the cost-effective measures to implement, but often also occurring over a long period and involving complex bureaucracy. Organising renovations on a multi-building scale can be co‑ordinated with local planning, easing co‑ordination among multiple stakeholders and speeding up the renovation process while reducing costs (for example, for renting scaffolding and buying materials). The IEA Energy in Buildings and Communities Technology Collaboration Programme (EBC TCP) is working to shed light on opportunities for district-scale renovations.

One notable development in building renovation business models is expansion of the Energiesprong programme, now active in five countries in Europe, where renovation or new build is financed by future energy cost savings plus the budget for planned maintenance and repairs over the coming 30 years. It has worked thanks to new technologies such as prefabricated facades, insulated rooftops with solar panels, and HVAC installations. While in certain contexts buildings are very different from one another and such “predefined” solutions might be difficult to apply, more countries are considering integrated home and building renovation services (e.g. one-stop-shops) as enablers for accelerating the renovation of existing buildings. For example, to stimulate the renovation market, Ireland is putting in place a national system to register the one-stop-shop providers, which will help enable the channelling of subsidies and ensure a more consistent customer experience.

Building energy codes and standards are among the “most widely recognised, scalable” and effective policy instruments for buildings, having been implemented in over 80 countries around the world, of which 70 cover the whole buildings sector (residential and non-residential). If nothing changes, this means that around 10 billion sq.m., more than the whole built surface of Germany and France conbined will not be covered by a mandatory building energy code for the whole sector.

Fortunately, many countries are considering developing or expanding building energy codes, even if no significant progresses happened in 2021.

Where building energy codes are already in place, continuous evolution of standards is essential to reflect and drive the current and future status of construction practices, materials and technologies.