When talking about energy efficiency in buildings, it is inevitable to mention thermal insulation. We rarely see it in a finished building and, even in the technical drawings, the insulating layer appears as a thin hatch. But this is an element that is of vital importance, as it acts as a barrier to the flow of heat, hindering the exchange of energy between the interior and the exterior, reducing the amount of heat that escapes in winter and the thermal energy that enters in the summer. In a building with good thermal insulation, there is less need for heating to keep the house at a pleasant temperature, also reducing its carbon footprint. Currently, there are many countries that require a minimum level of thermal insulation for buildings, with increasingly strict parameters. But how should this issue be dealt with in the near future, with the worrying climate crisis forecast?
According to the EPA (U.S. Environmental Protection Agency), rising global average temperatures are associated with widespread changes in weather patterns. Scientific studies indicate that extreme weather events such as heat waves and major storms are likely to become more frequent or more intense with human-induced climate change. But what does this have to do with architecture? The construction industry accounts for almost 40% of CO2 emissions. And a large part of this, 28% to be exact, is in the operation of buildings, which also use 36% of all energy demand on the planet, according to 2020 data from the Global Status Report for Buildings and Construction. This is where thermal insulation becomes important.
Heat losses or gains occur by convection, conduction and radiation. They will inevitably occur, but it is the designer’s duty to manage how quickly heat is lost or gained – this can be controlled through the use of appropriate building materials and techniques to establish and maintain an airtight building envelope incorporating high levels of insulation. Generally 40% of the heat transfer in a building is through the roof, up to 25% through the walls and up to 15% through the floor.
Working as much as possible with passive strategies for comfort, depending on where the project is located, will always be the best starting point for a more environmentally friendly building. Buildings in hot climates generally rely more on natural ventilation and materials with high thermal inertia (such as bricks or stones), which retain heat from the outside for longer, keeping the interior cool. In cold climates, materials with lower thermal inertia (such as wood) ensure that spaces are heated more quickly when necessary. In either case, insulation is critical to managing heat flows and protecting occupants from the outside weather, whether cold or hot.
To measure the values needed for each situation, there are some concepts to learn. R-value of insulation is related to thickness and the Lambda value of the insulation (Lambda is the heat conductivity of the material in W/mK). Doubling the thickness of the insulation doubles the R-value. Using material with lower lambda value increases the R-value. The U value, in turn, is the global heat transfer coefficient and can be found by taking the inverse of the R value. It is a property that describes how well building elements conduct heat per unit area across a temperature gradient.
The main insulating products currently on the market are glass wool, stone wool, polystyrene, polyurethane, cellulose and woodfibre. Each of these options has different qualities and attributes that can inform your choice of materials for a particular location. But there are also other materials, such as airgel, cork, straw, mycelium and hemp. A common property of the aforementioned is that they are light and able to trap a considerable amount of air.
It is estimated that adequate thermal insulation reduces heating and cooling costs by up to 30%, and that the cost of investment in insulating materials is recouped in up to 5 years, through reduced bills and even in reduced capacities of heating and cooling systems. If we consider the stock of existing buildings and the new ones to be built, we can measure the energy savings for a country or for the world. A EURIMA report, for example, concluded that 310 million tonnes of heating-related emissions in Europe can be avoided every year by applying state-of-the-art thermal insulation measures to new and existing buildings – around 50% of total emissions related to heating and well over 10% of total CO2 emissions. The environmental implications of the energy savings of insulation go right to the heart of global climate change, simply because less energy consumption means less greenhouse gas emissions.
Indeed, climate change will play an increasingly important role in the design of the built environment. Is it already important to think about shelters for an irreversible post-climate change scenario? Another aspect that weighs even more heavily on this topic, is that dealing with cooling is innately more difficult than dealing with heating. While any form of energy can turn into heat, and our bodies and machines generate heat naturally, even in the absence of active heating systems, cooling does not benefit equally from spontaneous generation, which becomes more expensive and complicated to implement. Global warming and its very tangible warming effects exacerbate this reality, intensifying an already accelerating demand for artificial cooling systems.
Is cooling interiors the biggest challenge of a future in which humanity has not been able to change its consumption patterns and voracious appetite for non-renewable resources? Will we have to build ever thicker envelopes to deal with the Earth’s warming? What will be the limit for that? Saint-Gobain’s book “Indoor Environment and Well-Being” summarizes this scenario well: “Both climate change and the changing approach to energy consumption will require buildings to be able to evolve over time. Rising energy costs and questions of its affordability for the majority of the world’s population will become increasingly pressing issues. A key factor in this evolution will also be an increase in critical reflection on what levels of thermal comfort will be considered acceptable, ie, should we just wear a jacket rather than raising the temperature of the system? The integration of such concerns into building design is known as ‘future proofing’ and will become an increasingly dominant topic at the forefront of building design discussions.”