1. Introduction
Recent research has shown that current UK housing, even that designed to the current Building Regulations is poorly suited to deal with the changing climate the UK is likely to experience over the next 50 years. This paper describes the design of a novel modular house, which aims to answer some of these short-comings and provide a cost-effective and reproducible solution to living within a changing climate.
Anthropogenic climate change is now an undeniable phenomenon [
1] and already in the UK, models of future climates have been developed, allowing architects and designers to predict the thermal performance of designs using predicted weather data for a range of climate scenarios over the next 70 years [
2]. The change in climate is not only to hotter drier summer conditions, but also to milder much wetter winters. These two changes create a new difficult scenario for the architects of housing where passive cooling needs to be factored into the design, along with flood resilience.
In addition, in the UK there is a great need for new affordable mass housing and indeed greater industrialization of the process that could bring better quality, speed and predictability to its delivery. However, in the UK, factory-made housing has not been able to provide the variety and flexibility necessary to respond adequately enough to differing site contexts and programmatic requirements. Therefore, rather than engage with modular solutions, UK house-builders have looked to use timber-framed solutions, to make a cost effective, high build quality solutions. This is not without its drawbacks: indeed much of the recently built, highly insulated, air tight, timber-framed housing is already suffering summer overheating. In addition it is also highly susceptible to flood damage. These are both risks that will be exacerbated in the future with climate change.
The Design for Future Climate projects are part of the UK Technology Strategy Board’s vision to support UK industry to develop innovation in new technologies. Climate change resilience is a key area of that work, where solutions are seen as holistic and design based, rather than technological add-ons. The IDEAhaus project as part of the Design for Future Climate, focused on two main objectives: firstly to assess the performance of current newly-designed housing within future UK climate scenarios, and secondly to develop a design for a new house that was affordable and could be easily replicated, which could adapt in a better and more passive way to the changing future climate context.
As the case study, the project took a proposed social housing development in Liverpool UK. This development consisted mainly of semi-detached and terraced low-rise houses, which were typically three bedroomed. Once the energy and thermal performance of these houses had been modelled utilizing UK Met Office climate projections through the century up to 2080 [
3], it became clear, that although these houses had been designed to current UK Building Regulations, the house type was unsuitable for the future climate change scenarios expected. The thermal analysis showed significant risks of overheating not only in the future, but also today, and also that the cooling demand for the house would exceed heating demand within 20–30 years. The houses had been designed to meet a scenario where heating in winter was the key driver, and had not considered issues of cooling.
Taking this performance data, the project developed designs for a building system for low-rise housing which would be more resilient to flood damage and better at resisting overheating through passive cooling techniques, such as shading, and the use of thermal mass and natural ventilation strategies. The system was to be based around a limited number of components which could be assembled to provide different sized homes, with a modular service/circulation core and a range of cladding options. The design illustrated how spatial flexibility, in-built flood protection, combined with thermal improvements and future adaptability could be used to develop an affordable but resilient house type that could cope with future extreme weather scenarios.
2. Future Climate in the UK
Climate change forecasting is an uncertain science. In the UK, the Department of Environment, Food and Rural Affairs have produced a range of Climate Projection scenarios known as UKCP09 [
4]. These cover a range of years (2030, 2050, 2080), emissions scenarios (low medium high) and probability (33, 50, 66 and 90 percentiles). The emission scenarios are based on future levels of carbon emissions, however it seems unlikely at present, that anything other than a high emissions scenario will be likely. The probabilities here are the likelihood of a certain climate being not exceeded, so the 90th percentile model is the most extreme with only a 1 in 10 chance being exceeded. Thus, this 90th percentile is a likely occurrence in one year in that decade. From these scenarios, the Prometheus Project at the University of Exeter [
5] have projected climate as a year-long set of results that mimic the CIBSE dsy (design summer year) and try (test reference year) data. The scenarios are in the form of hourly data, in Energy Plus format (epw) and can be used in most energy modeling software.
In general the anticipated pattern of change in the UK is toward hotter drier summers, milder wetter winters, stronger winds and more frequent, more extreme events such as heat-waves, storms and flooding. Climate change means that buildings will have to be, firstly more adaptable to cope with the changing climatic conditions, and secondly more resilient to cope with extreme events. Both these functions, will also have to happen within a changing energy and materials scenario, as oil diminishes and materials deplete. In addition, these two functional requirements, of adaption and resilience, are also not necessarily commensurate and create a complex design context, which can be difficult to negotiate.
The initial case-study was situated in Toxteth, Liverpool, UK. The current climate in Liverpool can be considered “mild maritime” with a January average of 6 °C and a July average of 13.5 °C. By plotting temperature and humidity data for the test years on a psychrometric chart, a bioclimatic analysis of the predicted future climate could be envisaged. Shown in
Figure 1 are the charts for 2010, 2030, 2050, and 2080, for one year in ten using a high emissions scenario (the most likely). This shows a gradual change in summer from a mild maritime climate to a more Mediterranean one. This is significant as there is a drift of temperatures during this period, across the comfort zone, developing from a heating dominated operation, to a more cooling orientated one. In addition to this, quantitative analysis of the data showed there is also a predicted increase in extreme wet weather in winter, with over 20% more rain during the winter months.
The current data (2010) from the Chartered Institute of Building Services Engineers’ (CIBSE) Design Summer Year (DSY) demonstrates clearly the current position: there should be very little need for any environmental control in summer, other than solar control. However, as we move into the future, the situation begins to change: by 2030 there is a need for a coordinated cooling strategy—say increased thermal mass. Continuing into the mid-century period, analysis of the DSY data showed that by 2050 even with a medium emissions scenario, there was a 50% chance (i.e., one year in two) that the summer would be similar in temperature and humidity to that of a Northern Mediterranean city, such as Lyon, France. By 2080 the predicted weather had altered again: the data for 2080 with a high emission Scenario with a 90% chance of not being exceeded, gave a very different summer climate, one more similar to that currently experienced in Rome, Italy. In this scenario the increase in average summer temperatures would be an astounding 9 °C and the maximum temperature some 11 °C higher than experienced today.
Figure 1.
Changing climate: bioclimatic charts: 2010–2080, Liverpool, UK.
Figure 1.
Changing climate: bioclimatic charts: 2010–2080, Liverpool, UK.
3. Analysis of Baseline Scheme
Studies such as the UK Technology Strategy Board’s Design for Future Climate [
6] have shown that housing in the UK, even new housing is being designed and built with little or no consideration of the changing climate. In his book, Bill Gething [
7] claims that we are now beyond climate mitigation in that the emissions already produced will cause unfettered climate change throughout the century, and thus we must now embark on a program of adaptation. This adaptation will have to engage with both new build and retrofit schemes, as much of the built environment of 2050 is already in existence. Retrofit ideas are already well documented, some involve fabric measures such as the addition of shading devices, or passive cooling techniques, whilst others involve the adaptation of the landscape in which the properties sit, to suit warmer and wetter conditions [
8].
The IDEAhaus concerned itself with the new build market, particularly that for low cost housing suitable for rental. In this market in the UK, housing design is highly regulated, particularly with regards to spatial standards, life-cycle costings, and energy use. The energy use of the house is modeled using an approved energy model known as the Standard Assessment Procedure (SAP) developed by the Building Research Establishment [
9]. This model, originally based on a modified degree-day type calculation only really concerns itself with heating (and lighting), thus houses are adapted specifically for cold, not warm weather, that is for heating and not cooling.
By considering a housing scheme already designed as a baseline, the project aimed first to critique current practice and assess the performance of housing that met the criteria with respect to the climate that the houses will face in the foreseeable future. From this critique, a new modular house was designed with a customizable façade, which was designed with the future climate and weather in mind. One that was robust and energy efficient, but also comfortable for the occupants.
The baseline scheme for the project was an existing design for Plus Dane Housing Association that was proposed to be built in the near future. The site was located in Toxteth, Central Liverpool, UK (see
Figure 2). This scheme was used to develop the base condition for comparative thermal and energy modeling, for different constructions within the same site layout. The layout of housing on the site adopted a diagonal solar orientation with houses facing SW, SE, NW and NE in square urban block arrangements.
Figure 2.
Housing layout, Toxteth, Liverpool, UK.
Figure 2.
Housing layout, Toxteth, Liverpool, UK.
A typical 3-bedroom 5-person, 2-story, semi-detached/end terraced house (
Figure 3) with traditional elevations was selected. The construction specification was for a high performance closed panel timber frame system. The fabric, designed to current UK Building Regulations (REF), was therefore highly insulated (wall, floor and roof
U-values at approximately 0.1 W/m
2K) and reasonably airtight (5 m
3/h/m
2) but not so airtight that it required a whole house Mechanical Ventilation with Heat Recovery (MVHR) system: the house was naturally ventilated in both summer and winter.
Figure 3.
Baseline 3-bed 5-person-house type.
Figure 3.
Baseline 3-bed 5-person-house type.
Initially, detailed thermal modeling using 2010 climatic data was carried out with IES software for each orientation of the properties on site. However the different orientations of the house type made very little difference to the thermal modeling results with regard to internal temperatures and energy use. The most likely reason for this being that the front and rear elevations had similar proportions of glazing and that the diagonal solar aspect (SE/NW) of the layout tended to equalize the exposure to sunlight, so a property with a SE orientation was chosen for the further comparative analysis.
Table 1 illustrates overheating in a typical SE facing double bedroom in the timber-framed designs. In the UK, CIBSE guidance recommends that internal temperatures should not exceed 25 °C for >5% of annual habitable hours and 28 °C for less than 1% of the hours [
10]. This guidance is not currently applied to single dwelling-houses in the UK but is used in other residential buildings. The detailed modeling used 2010 CIBSE Design Summer Year (DSY) data and compared this with a “worst case scenario” that being the hottest summer in the decade around 2080. (This equates to 2080 DSY, with a high emissions scenario, 90th percentile projected weather set from the Prometheus database.) Findings showed that overheating in bedrooms (internal temperature above 28 °C) would occur for 6.6% of the time in 2010 rising to 50.5% of the time in 2080. If only the summer months of July and August are considered, this would equate to 28.4% of the time in 2010 and 74.6% in 2080. Peak internal temperatures experienced in the bedroom are 35 °C in 2010 and 39 °C in 2080. The conclusion inferred from this analysis is that the current house type is inadequate with respect to summer over-heating, as the internal overheating is already well above the CIBSE guidelines now, and becomes severe by 2080.
Table 1.
Summary of internal overheating modeling (IES) on baseline house-type for SE facing bedroom in 2010 and 2080* Hi-emissions 90th percentile.
Table 1.
Summary of internal overheating modeling (IES) on baseline house-type for SE facing bedroom in 2010 and 2080* Hi-emissions 90th percentile.
CIBSE | Guidelines | Period | Peak Temp | Int Temp | >25 °C | Int Temp | >28 °C |
---|
(°C) | (h) | (% Time) | (h) | (% Time) |
---|
Timber-framed | 2010 DSY | annual | 35 | 573 | 19.6 | 192 | 6.6 |
house | | July/August | 35 | 310 | 62.5 | 141 | 28.4 |
| 2080* | annual | 39 | 2605 | 89.2 | 1474 | 50.5 |
| | July/Aug | 39 | 496 | 100.0 | 370 | 74.6 |
Masonry | 2010 DSY | annual | 29 | 396 | 13.6 | 81 | 2.8 |
house | | July/Aug | 29 | 286 | 57.7 | 42 | 8.5 |
brick/block | 2080* | annual | 33 | 1391 | 47.6 | 934 | 32.0 |
| | July/Aug | 33 | 496 | 100.0 | 262 | 52.8 |
Next, a similar analysis was performed on a similar house, that was designed utilizing what would be considered a “traditional” UK building method, namely a masonry construction of brick external skin and medium weight concrete block inner, with a wet plaster finish. This change of construction shows a significant reduction in overheating, with the house being above 28 °C for 2.8% of the time above in 2010, and 32.0% in 2080. Results for July and August show overheating for 8.5% of the time in 2010 and for 52.8% in 2080. Peak internal temperatures are also significantly reduced at 29 °C and 33 °C respectively, but these are still high.
Further energy modeling of the timber framed house was carried out using Sefaira Concept software [
11]. This produced an energy consumption analysis based on the UK Government’s SAP analysis [
12].
This analysis shows the energy footprint in kWh for the heating, hot water, lighting and power for the house (see
Figure 4). It is clear that the space heating demand (red) reduces considerably to a minimal level by 2080. Hot water, lighting and appliances (yellow, orange and green) are constant. The modeling was then repeated with the addition of air-conditioning for comfort cooling; switching on at 25 °C (
Figure 5).
This analysis shows that reduced demand for heating (yellow) that occurs in 2080 is counteracted by an increasing cooling demand (blue), and thus the overall energy demand for the house would actually increase over time. Further IES analysis shows that energy demand for cooling in the house could overtake its heating demand before 2040 in a 90th percentile year (
Figure 6).
In fact, the “carbon crossover” rather than the energy crossing would, in practice, arrive even earlier, as cooling energy is generally more carbon intensive (with cooling being produced using electricity) than space heating (from gas central heating) in the typical UK situation. The team therefore concluded that if we are to design for future climate as well as the present, then summer performance will become more crucial and will need to be accommodated in today’s designs. In fact, the importance of winter performance and heat loss as a design strategy will diminish and more attention in the future will need to be paid to overheating and reducing the demand for cooling and summer energy use.
Figure 4.
Energy analysis for 2010 and 2080 high emissions scenario 90th percentile energy analysis.
Figure 4.
Energy analysis for 2010 and 2080 high emissions scenario 90th percentile energy analysis.
Figure 5.
Energy analysis with air-conditioning at 25 °C set point for 2010 and 2080 high emissions scenario 90th percentile.
Figure 5.
Energy analysis with air-conditioning at 25 °C set point for 2010 and 2080 high emissions scenario 90th percentile.
Figure 6.
Timber frame—Space Heating versus Cooling energy demand in the house using high emission scenario 90th percentile projections.
Figure 6.
Timber frame—Space Heating versus Cooling energy demand in the house using high emission scenario 90th percentile projections.