L. Shao,     De Montfort University, UK

25.1 Introduction

It is estimated that the new buildings constructed between now and 2050 could account for one-third of the total building stock in 2050 in the UK (Glass et al., 2008). Although their volume is smaller than that of the existing buildings, they are highly significant not least because they are best placed to achieve the best levels of carbon reduction performance, and help set the standard for all buildings. The difficulty is enormous though. The government has set the target for all new dwellings to achieve zero carbon emissions by 2016 and all new non-dwellings to achieve the same by 2019. The protracted and complicated discussion about the definitions of zero-carbon has revealed the tip of the iceberg of the challenges, which are diverse and dynamic.

The following discussion is not meant to be comprehensive, which is beyond the scope of this chapter. It will instead highlight some current and acute challenges facing the new build construction sector, e.g., genuinely delivering carbon savings at levels as originally intended in the design, and balancing carbon reduction with adaptation to the future climate. These will be illustrated with discussions about a number of sustainable material technologies in new buildings – thermal mass, PCM, and vegetation and high albedo building surfaces. Some of the other important issues, such as glazing, will not be one of the foci as they have been covered more extensively elsewhere. The current and future legislations will also be discussed as will the interdependency among future climate, buildings and lifestyles.

25.2 Challenges facing the new build construction sector

25.3 The role, shape and trend of legislation

The building energy related legislation is playing a crucial role in driving up the carbon and energy performances of new buildings. Energy and carbon prices are not high enough, yet, to become a major driver of the change. The wide awareness of climate change has not been translated into actions of similar magnitude. A study published in 2008 for NHBC by the research organisation EPR found that energy efficiency was not a major factor in the purchase of a new home. A better kitchen or bathroom has a higher priority in the minds of potential buyers. Although the majority of the UK population are taking some form of action to reduce energy use, including using compact fluorescent lamps to replace GLS versions, turning off lights and recycling domestic waste, much less is being done to major areas of energy consumption such as heating. Legislation will remain as a main driving force in the near future.

So far a key piece of legislation has been the EU Energy Performance of Buildings Directive (EPBD), adopted in 2003. This was implemented in the UK in 2006. In England and Wales, this was in the form of the 2006 revision to Part L of the Building Regulations and the Energy Performance of Buildings (Certificates and Inspections) Regulations. The revisions to Part L were set out in four Approved Documents published in April 2006. Two of these relate to new builds – L1A and L2A, for new dwellings and new non-domestic buildings, respectively.

The 2006 Approved documents stipulate that carbon emissions of new buildings must be lower than a calculated target value, that specific building components must exceed threshold performance levels and that the building must not overheat without active cooling. The requirements and assessment procedures for overheating prevention differ for dwellings and non-dwellings, allowing a range of possible tests, including those based on solar gains, overheating periods or building design/use details. The standards of construction, commissioning and provision of information to the building owners are also covered. Energy and carbon emission calculations were based on Standard Assessment Procedure (SAP) and SBEM (Simplified Building Energy Model) or DSM (Dynamic Simulation Model) for dwellings and non-domestic buildings, respectively. Compared with the 2002 Regulations, the 2006 Regulations represent carbon reductions of 20% for domestic buildings. Similarly, the reduction for non-domestic, non-air-conditioned buildings is 23.5% and for non-domestic air-conditioned buildings, 28% (CIBSE, 2008).

The 2006 Approved Documents represent significant advances but it is an interim step in a programme of rapidly evolving legislation. Certain areas of the regulations are underdeveloped, e.g., assessment of overheating in new dwellings using SAP Appendix P could be significantly upgraded by setting more stringent requirements. The many aspects of oversimplification, e.g. in building use profile, weather, ventilation and thermal dynamic processes, could also be improved. The overheating assessment of non-domestic buildings is also affected by similar problems, though to a lesser extent at this time. In addition, the overheating criteria should be examined and updated to more accurately reflect the severity and impact of overheating (CREW: http://www.extreme-weather-impacts.net/twiki/bin/view), and take into account the future climate patterns. Given numerous reported incidents of overheating in domestic and non-domestic new builds, even under the relatively cooler current climate, this aspect of the building regulations should receive greater attention.

The implementation of the EPBD also resulted in the Energy Performance of Building (Certificates and Inspections) Regulations 2007, which requires an Energy Performance Certificate (EPC) for all buildings when built, sold or rented. Furthermore, it requires a Display Energy Certificate (DEC) for all public buildings larger than 1000 m² and regular inspection of air conditioning systems with cooling capacities larger than 12 kW.

In 2007, the CLG issued a policy statement (CLG, 2007) confirming the government’s plan for new homes to be zero carbon by 2016 and new non-domestic buildings to be zero carbon by 2019. The CLG outlined a staged implementation of the policy – further enhancement of Building Regulations in 2010 is expected to reduce new build carbon emission by 25% compared with the 2006 Approved Documents and the Building Regulations revised in 2013 and 2016 would result in 44% carbon emission reduction and zero carbon emission from new dwellings, respectively. Note that zero carbon represents over 100% reduction because the 2006 Approved Documents only regulate certain categories of energy use (water and space heating, lighting but not appliances, cooking and cooling). A zero carbon dwelling would require about 150% carbon emission reduction from a level represented by the 2006 Approved Documents (NHBC Foundation, 2009).

Closely related to the zero carbon homes agenda is the Code for Sustainable Homes (CLG, 2008b), which is an energy and environment rating system for new domestic buildings. Among the nine categories of sustainable design issues is energy use and carbon emissions of the dwelling. Homes achieving the best level of the Code, Level 6 will have achieved zero carbon emissions, while those at Level 5 will have achieved 100% reduction compared with the 2006 Approved Documents. The reductions for levels 1 to 4 are 10%, 18%, 25% and 44%, respectively.

At the time of writing the definition for zero carbon in new homes was going through a consultation process initiated by the CLG (2008a). As shown in Fig. 25.2, the proposed definition of zero carbon involves not only carbon emission levels but three separate factors – energy efficiency (e.g., the insulation standards of the building fabric), carbon emission levels and allowable solutions which may include approved investment and export of renewable heat. The complex system could allow a new home which emits carbon dioxide to be labelled zero carbon. The situation, although controversial and confusing, does serve to highlight the enormous practical difficulty of achieving zero carbon through technical means alone. Substantial lifestyle change, which reduces demand and facilitates implementation of renewable technologies at various scales, would be necessary.

The power of legislation and regulations is reflected in the Merton Rule – local planning requirement that 10% or more of the energy supply of a new building should be from on-site renewables. The regulation has been exceptionally effective in promoting a range of energy technologies, including the Ground Source Heat Pump, which is more expensive than higher levels of insulation and other more basic technical interventions. While invaluable for promoting the implementation of renewables, it does point to a need for more integrated policies and legislation that will enable balanced approaches to carbon emission reduction that maximise carbon performances.

In November 2008 the UK adopted the Climate Change Bill which set a legally binding target of at least an 80% cut in greenhouse gas emissions by 2050, against a 1990 baseline (DECC: http://www.decc.gov.uk/en/content/cms/legislation/en/content/cms/legistation/cc_act_08/cc_act_08.aspx). Against this backdrop, the tightening of carbon emission requirements in the building regulations is set to continue, although their impact will be dependent on a multitude of factors, not least a culture of delivering real performances. Crucially, there should be stringent requirements for the new builds to adapt to the future climate, particularly the heatwaves and other extreme weather events. Embodied energies in new buildings, and life cycle energy use are also important factors to consider in future building energy legislation.

25.4 Thermal mass

This section illustrates some of the key challenges for new builds by focusing on a significant material-related issue – thermal mass. This is a particularly appropriate issue for the new build sector as adding substantial thermal mass in the renovation of existing homes would be more difficult.

There are two principal applications of the thermal mass. The first is to use it as a form of thermal storage for passive solar or other thermal gains. For dwellings, the heat stored during sunny daylight hours, for example, is released during the occupied hours at night, thereby reducing or removing the need for space heating. In the second type of application, the thermal mass absorbs the heat during the day in summer, thus reducing the peak temperature and improving thermal comfort. The higher thermal mass will result in smaller temperature fluctuations between night and day and also a phase shift of the daily temperature cycle, both of which could be utilised through appropriate design to bring about a cooler indoor environment during hot weather.

As explained in Section 25.2.1, the real performance could be quite different from predictions. It was reported by Tuohy et al. (2004) that several tests involving high- and low-mass houses showed that higher mass resulted in more heating energy consumption. The CIBSE Guide F (2004) also stated that high-mass buildings which are intermittently heated (as opposed to continuously heated) tend to consume more heating energy than low-mass ones adopting the same heating patterns. On the other hand, a Concrete Centre report (2006) quoted energy savings of up to 11% for masonry and concrete dwellings compared with lightweight counterparts, based on several computational studies commissioned by the concrete industry in 2005/6. Quoting further research commissioned by the concrete industry, the report stated that a typical two-bed semi-detached house in South-East England could save carbon emission of about 150–350 kg p.a. on average over the 21st century.

A piece of work which helped resolve the conflicting claims was that by Tuohy et al. (2004), who carried out a well constructed programme of simulation based on two simple and similar buildings which they referred to as (Brenda and Robert) Vales Rooms, which featured low and high thermal masses. The low-mass building contained only lightweight elements e.g., plasterboards, within the insulation envelope while the high mass building was constructed primarily from concrete within the same insulations.

The research showed that higher thermal mass could result in less, similar or more heating energy consumption depending on three levels of insulation. Energy savings improve with insulation levels. The higher heating energy consumption at a lower level of insulation is a result of a larger amount of heat required to heat up the building fabric which subsequently leaked out to the environment. The work further revealed that higher thermal mass is more likely to save energy when used in the warmer southern climate of the UK than in the North and when there is a high continuous occupancy. Combining northern climate, weekend occupancy only, and lower insulation level could mean that the high-mass building consumes 50% more energy for heating. The impact of infiltration/ventilation rate is similar to that of the insulation level – higher mass buildings tend to perform better when the building is more airtight. This piece of research revealed that higher mass is not directly linked to energy savings and that the insulation and infiltration standards of the construction may significantly sway the relative attractiveness of high-mass building over lower mass ones. The relative success of the high-mass Hockerton housing development is a testimony to this principle: All houses were super insulated and meticulous attention was paid to minimising thermal bridge and infiltration. As insulation and infiltration levels are important factors, the standard of construction is therefore crucial. The multitude of influencing factors also means that it would be necessary to simulate each new building individually during the design process to determine the best level of mass – there is no fixed rule in this regard.

A significant conclusion regarding thermal mass of new buildings is that under the current building regulations, the energy consumption of a new building is unlikely to be substantially influenced by the level of thermal mass. Indeed, the Passive House standard does not specify a thermal mass requirement.

In contrast to the variable winter energy saving performances, the effect of high thermal mass on reducing summer overheating is more significant. Givoni (1998) reported his measurements on two houses in Southern California with identical U-values but significantly different levels of thermal mass (0.5″ plasterboard vs 10 cm concrete inside external insulation, for the low- and high-mass buildings, respectively). The higher mass building achieved up to 3 K reduction of peak indoor air temperature, which is further reduced by about 1.5 K when night time ventilation between 7 pm and 7 am was implemented. The simulation work by Tuohy et al. (2004), based on buildings of similar contrast of high and low thermal mass levels, indicated similar levels of temperature reductions for the high-mass building.

The impact of night time ventilation is affected by local climate, being less effective for certain parts of the southern European countries around the Mediterranean. It is also influenced by how the ventilation air flows across the room, by the room surface covering and the presence and utilisation of hollow-core structure elements such as the TermoDeck panels. It is certain, though, that night time cooling works better with higher mass buildings (Tuohy et al., 2004).

As with many other technologies, the high thermal mass design could introduce conflicting design requirements for winter heating and summer cooling – and require ‘joined-up’ thinking. Winter heating is often optimised by utilising passive solar design, which feature certain elements like sun spaces with large glazing areas which are not always easily openable. The best effect of high mass for summer cooling is achieved with night time ventilation, which is often not facilitated by the glazed sunspaces. Fortunately the choice would not be too difficult to make.

For high-mass design the priority should be placed on passive cooling considerations, as this is the area where the benefit is significant, consistently achievable and where we meet some of the most significant challenges imposed by climate change on future buildings. The sunspaces will gradually become much less used. The evidence comes from both technical analysis and comparative observation. If the climate of Britain is to become more like that of the Mediterranean region, the shape of building there now can serve as a useful indicator of buildings of Britain in the future, although not literally. The choice of design should be based on detailed modelling and analysis using the appropriate weather and occupancy/activity patterns, rather than copying. The challenge of climate change is unprecedented, particularly in terms of extreme weather events such as heatwaves. In this sense, what the UK could experience in the future may be quite different from what has been happening around the Mediterranean.

An exception to using high thermal mass in buildings for passive cooling is the stilt houses found in hot and humid climates such as in Thailand or Malaysia (see Fig. 26.3 (a) and (b)). Here the buildings not only have low mass themselves, but are also deliberately decoupled from the thermal mass of the ground. Although high mass will bring a reduction of peak indoor temperatures it will, on the other hand, raise the minimum temperature as heat absorbed during the day is released. The stilt houses, containing very low thermal mass, ensure cool room temperatures at night, creating the optimum conditions for restful sleeping. In contrast, high mass and wellshaded colonial buildings in tropical regions work better during the day, as borne out by thermal comfort studies in these regions (Sanusi, 2006).

A variation of the high-mass design is the earth labyrinth, which makes use of the large mass of the ground and the stored coolness there. Compared with conventional thermal mass, it is switchable although the radiative and conductive benefits of high-mass elements in the living space are not available. In operation it is more like an earth-air heat exchanger so will not be discussed further here. An insightful review of this topic is provided by Pfafferott et al. (2007).

25.5 Phase change materials (PCMs)

A further variation of the high-mass design is to implement phase change material (PCM) components in the building. As the scope of the discussion is construction materials rather than mechanical systems, the following discussion will be confined to building components containing PCM, particularly PCM wallboards.

Although the mass of the PCM itself is not high, the substantial latent heat involved in the phase change process enables the PCM components to absorb/release heat as if it has a much higher thermal mass. As such, one would expect that performance characteristics of thermal mass, e.g., insignificant winter energy savings, would hold true for PCM components. This is true but only to a certain extent.

The low impact of PCM on heating energy savings is confirmed by recent research, as reported by BASF AG (2006). It was found that the incorporation of PCM plasterboard (melting range: 21–25 °C, 26% PCM by weight) in lightweight buildings had little impact on the heating load. The effect on cooling load is greater but the impact on carbon emissions is significant only if the use of installed air conditioning is minimised. The BASF study is well organised and detailed though based on computer modelling. The thermal conduction and heat storage in the PCM plasterboard were calculated using the dynamic building simulation program DYNBIL from the Passiv Haus Institut.

Good quality experimental results were available from a study carried out at the Fraunhofer Institute (Schossiga et al., 2005) in two full-sized test rooms in the Fraunhofer façade test building. Two identical well-insulated low-mass rooms were fitted with PCM (40% by weight) and conventional plasterboards, respectively. The PCM has a melting range of 24–27 °C. During a three-day monitoring period, the rooms were subjected to night time ventilation but were not shaded. Air temperatures in both rooms started off with identical values but diverged once they reached 26 °C. The peak air temperature in the PCM room was over 3 K lower than the conventional room but even on the first day the PCM was fully discharged before the temperature peaked. Even with night time ventilation, the PCM did not get fully charged so during the following day the temperature reduction dropped to just over 2 K and this narrowed to less than 1 K on the third day.

The results showed the crucial importance of allowing PCM to fully recharge and matching the PCM capacity with the cooling load thus preventing complete PCM discharge. These were achieved by providing shading to both rooms and the results showed sustained temperature reduction over a seven-day test period, though the level of peak temperature reduction was reduced to less than 2 K as the PCM plasterboards were not stretched to full capacity.

It was also clear that the PCM plasterboard had limited effect for room temperatures below 26 °C and it is more effective for reducing temperatures above 28 °C as the PCM would be more active. During a 20-day test period the conventional room was warmer than 28 °C for 50 hours, compared with 5 hours for the PCM room. These, of course, would change with internal gains and other factors in an occupied building.

The need for appropriate design is again highlighted by the results of another set of tests on full-sized rooms fitted with PCM and conventional plasterboards (Feng et al., 2005). The melting range was 19–22 °C. These would be very comfortable temperatures if the indoor temperature could be held close to this range. However, even the night time outdoor temperature rarely dropped below 22 °C during the test period so the PCM was not able to charge at all. Consequently, the air temperature in the PCM room is practically identical to that in the reference room (PCM room is 0.2 K lower on average).

The above highlights a practical design issue with PCM – unlike conventional thermal mass which would moderate temperature oscillations at all temperatures, the PCM does so only within a limited temperature band, centering on its melting range. Beyond this range, it will not function. Put in somewhat oversimplified words, a building considered to be high-mass because of its PCM components will be high mass only within a limited range of temperatures, beyond which it will behave as a low-mass building. In addition, the conventional thermal mass will function the same way regardless of the magnitude of the heat load it is subjected to. The PCM, however, has an upper limit imposed by its latent heat capacity, beyond which a PCM ‘high-mass’ building will again behave as one of low mass.

In this context, PCM plasterboard intended for mitigating overheating of buildings in summer should have melting temperatures set close to the upper threshold of thermal comfort as the above test results have indicated. Setting lower melting temperatures could result in more days of very comfortable temperatures but no effect on the uncomfortable hot days. In mixed mode spaces, however, the melting range should be lower than the AC set point and the recharge should be by night time free cooling.

In terms of balancing the requirements for winter heating and summer cooling, it is very difficult to reconcile the need for passive solar design in winter and passive cooling in summer if PCM is the common element of thermal storage for both, because the required melting ranges would be well apart from each other. One solution might be to implement interchangeable PCM panels but the quantity required present significant practical difficulties.

The range and capacity limitations of the PCM is particularly significant for dealing with exceptional heatwaves, when its design melting range could be well below the extreme temperatures and the design capacity of the PCM component could be overwhelmed, resulting in a low-mass shell that offers little thermal protection against the high temperatures. This is compounded by higher night temperatures which make recharging difficult, particularly during still, windless nights.

The conventional thermal mass is superior in terms of the issues outlined above. However, our discussion has been limited to the construction’s components without considering wider PCM-based devices. Furthermore, the issues of construction cost and maintenance have not been discussed either.

25.6 Vegetation and reflective materials

It is very likely that reflective materials and vegetation will be utilised more widely in the future because of their potential for reducing building overheating, preventing or minimising the use of air conditioning, and also mitigating the UHI. In this chapter, however, our focus is on building-related applications including reflective roofs, green roofs and green walls.

The structural, drainage, safety and other requirements of the green roof suggest that it is more easily implemented in a new build. Although there have been many years’ research on their performances based on computer modelling, the availability of good quality data obtained from tests on real buildings is limited.

Tests carried out in Greece by Niachou et al. (2001) showed that the green roof installed on an insulated ceiling brought about reductions of room air temperature of 0.5–2.0 K, averaging about 1 K over the three test periods. The period when the indoor temperature was over 30 was reduced 70% to 15% in one of the monitoring periods. The tests were carried out when the buildings were not occupied so that the air conditioning could be switched off to remove its effect on indoor temperature results. Switching to modelling, the study showed that the total energy saving including those from both heating and cooling seasons would be insignificant at 2% if the roof supporting the vegetation is well insulated (e.g., 10 cm insulation sandwiched between 10 cm concrete elements). This saving would be dramatically increased to 37% if the roof is uninsulated (e.g. bare 10 cm concrete). However, in the context of new builds, this is rather improbable.

A further test programme in Greece measured the effectiveness of green walls (Eumorfopoulou and Kontoleon, 2009). A six-storey building was used and the external surfaces of the lower three storeys were covered with climbing plants (Parthenocissus triscuspidata) to an average thickness of 25 cm. A room on the second floor and another on the third, on the east facing façade were used in the study. Comparison of the temperatures taken on the external and internal surfaces of the rooms showed that the vegetation reduced the external surface peak temperature by up to 6 K, averaged over the month-long test period. The peak temperature of the internal room surface was reduced by 0.9 K.

Although the shading and evaporation provided by the leaves of the plants may help to reduce the roof external surface temperature and help to alleviate indoor overheating (as well as UHI if widely adopted), the same process may be detrimental to winter energy efficiency of the building.

An alternative to vegetation is to adopt high reflectivity materials and coatings to the roof and other external surfaces of a building. The latter shares many of the benefits of the vegetation-based installations but is very often much simpler and cheaper to install. Of the many tests, a more recent one on high reflectivity roofs was carried out in Australia (Suehrcke et al., 2008), in which room and surface temperatures were measured before and after the application of a high reflectivity white paint (albedo = 0.8). Indoor air temperature reductions of about 1 K were recorded. Akbari (2007) reported his work on monitoring high reflectivity roofs in buildings in California and found that the cooling energy reduction varied from as low as 3–4% to 52%.

Installation of high reflectivity roofs, as in the case of green roofs, could result in greater use of heating energy in winter. Akbari (2007) estimated that the winter heating penalty could be up to 5%. The overall energy saving taking into account both heating and cooling energy use varied dramatically with local climates. For example, savings for buildings in Philadelphia would be typically negligible. Akbari stated that in the United States, cooing energy benefit in summer is normally greater than winter penalties. However, for the UK where active cooling in summer is not as widespread, the application of high reflectivity roofs could result in a net energy (and carbon) penalty.

Both the green and high reflectivity roofs and walls could have an energy disadvantage during the winter heating season. However, this should be considered against the potential energy increase associated with active cooling if passive cooling such as a high-albedo roof is not available. In the longer term, the UK heating requirement would reduce while the cooling load would rise, thus the cool roof installations would gradually become more effective in terms of both energy and comfort. They also, of course, make an additional and very beneficial contribution to reducing the UHI intensity.

A green roof and a white or high reflective roof are not directly comparable as they have significantly different constructions. However, as shown above, their potential for passive cooling and energy savings are broadly similar in the applications considered. They have different levels of structural complexity and installation costs. In addition, maintenance requirements are different. For example, during prolonged dry hot spells when the green roof is required to work harder to shelter the building, it is weakest facing levels of stress that threaten its own health. Regular maintenance and partial replanting where needed is necessary.

In terms of thermal performance, there is little reason to favour green roofs or walls. A well planned and executed test programme carried out by Takebayashi and Moriyama (2007) showed that among five roof materials tested – high reflectivity white paint, green roof, bare soil, high reflective gray paint, and cement concrete – the material that generated the coolest surface temperature was consistently the high reflective white paint, both in summer and winter. This finding is not exactly surprising as it reflects the postcard images of the white painted villages on the Greek islands in the Mediterranean (Fig. 25.4).

On the other hand, the numerous benefits of urban vegetation, including flood risk mitigation, promotion of biodiversity, health and well-being, as well as their cooling properties, mean that green spaces will be increasingly valued and used, as will well designed and regularly maintained green roofs and walls. The importance of many of these benefits are recognised by prominent building rating systems including the Code for Sustainable Homes, BREEAM and LEED.

25.7 Future trends

The future of buildings is zero carbon, just as they have to be sustainable in many other aspects. Yet reaching that goal is difficult, as illustrated by the discussions about the definitions and pathways to zero carbon, and might require substantial lifestyle changes as well as technological advances. The lifestyle change is difficult to predict, particularly in the longer term. But certain trends are emerging. For example, it was pointed out that the higher temperatures in future could mean a gradual shift towards more outdoor living and parks and green spaces could be used more intensely (Greater London Authority, 2008). Lifestyle changes in turn will impact on building design, green roofs could have more of a social dimension and become better maintained and more popular, building could become more open and connected with the outside spaces.

Heightened awareness of energy use could mean that people adopt a lifestyle that is more responsive to our local and seasonal climates rather than a more uniform one throughout the world and throughout the year. Taking a siesta during summer could alter passive cooling requirements and designs. Likewise, people in hotter climates may come to accept higher temperatures and those in cooler climates accept lower temperatures. This may have implications for the pace of life and type of work that people may choose to adopt, which in turn may translate into different building design requirements. Regional difference and diversity could increase.

For the more immediate future, there is a great need for high quality real performance data on the new build and the impact of materials on its carbon emissions and climate adaptation. The evolution of building design has to a very large extent been propelled by the advancement of materials. While their development in the past has allowed buildings to become ever taller, larger, stronger and more comfortable, their success in the future will depend more on their contribution to making buildings fit for an unprecedented future, where the lifestyle is necessarily zero carbon and the climate warmer and more extreme.

25.8 Sources of further information and advice

25.9 References