Knowledge gap

As discussed in Section 2.1.1, it is required in research and innovation activities to conduct ongoing monitoring to assess the actual performance of the buildings against the modelled predictions. As SIP offers improved thermal performance, low embodied energy and carbon emissions, it is considered as a potential material which reduces the building environmental impact. Besides, promoting MMC by using SIP construction helps resolving shortage in housing supply and labour skills.

In addition, changes in building regulations meant an increase in insulation levels in the effort of reduce energy demand for heating leads to a rising risk of overheating. Homes built using certain MMC configurations (SIP included) that do not incorporate thermal mass are more sensitive to any alteration in heating and cooling energy inputs. Indeed, it is reported that overheating risk increases as a result of increasing levels of insulation and decreasing on thermal mass level in not just summer but also spring and autumn (Orme and Palmer, 2003). The modelling work carried on to identify peak temperature

and degree hours in four houses types then investigates the influence of each possible measure to alleviate the overheating. The study found that the more highly insulated house presents 16% increase in overheating hours in comparison to the base case dwelling set in the Building Regulations (Orme and Palmer, 2003). However, the overheating risk could be resolved by implementing a combination of passive cooling techniques. The case studies showed a reduction of 70% of overheating degree hors and that the internal temperatures stayed 2.5 C lower than the external temperature through using the combination of mass, night cooling, solar protection and reduced internal gains (Orme and Palmer, 2003: p29). Or another study looked at eliminating overheating risk by number of cooling socio-technologies traditionally employed such as shading from the sun, thermal mass to stabilise temperature, passive heating and cooling systems and afternoon siestas (Hacker et al., 2005).

There is therefore a rising need of conducting overheating risk assessment for SIP construction. SIPs have been used in all kinds of climates, in hurricane zones and earthquake belts but, in the relatively tame UK, SIPs were perceived to be just a little bit too expensive to bother with. But the benefits of reduced construction cost with less time building and less labour and reduced energy cost from lower operational energy by improved performance should be taken into account. Whether the total construction cost of SIP building is lower than conventional building, it depends on the considered circumstances, including local labour conditions and the degree to which the building design is optimized for one or the other technology. For a full comparison of SIP construction with any other building materials, a life cycle cost is required.

It is then identified that the knowledge gap is as below:

 SIP is potentially a building material which helps reducing the building environmental impact. However, there is a lack of evidence of real performance of SIP construction in the UK. As a solution of MMC, a question of whether SIP ensures to bridge the gap in performance existing in the traditional constructive method.

 Overheating risk in lightweight construction has been perceived to be an issue and SIP with good insulation and airtightness levels might result in worsening the condition. With the temperature getting warmer, there is a greater risk of overheating inside UK houses as most of them rely on natural ventilation for cooling design. Thus, it is important to investigate the overheating risk in SIP

construction with integrated passive design solutions (ventilation, shading and thermal mass).

 SIP is perceived to be more expensive than traditional building materials and its benefits in energy savings are somehow still hidden to the customers who show more interest in putting insulation in cavity (wall and roof loft) to meet the Building Regulations. Thus a cost benefit study to compare typical construction using SIP and traditional building material is needed to demonstrate their cost implications.

2.4 SUMMARY

The house building industry is under pressures of shortage in housing supply and labour skills, poor quality of current housing stock built by traditional methods, need of affordable homes. These emerged by mandating improved energy efficiency by Building Regulations and UK Government’s legal binding of carbon emission reduction with zero carbon homes built from 2016 onwards. This urges developers to implement innovative and energy efficient design strategies to generate zero carbon homes by 2016.

Some success has been achieved by the use of SIP, a composite of wood and insulation material, which have much improved thermal properties when compared to traditional materials like brick, block. In addition the use of less traditional material allows offsite construction and ease of assembly, thereby providing potential to significantly reduce embodied impacts, both in the short and long term. Reductions occur in the short term through easier construction using light weight materials and long term through enhanced thermal performance throughout the year. It is also interesting to note that with controlled and highly precise design and manufacturing through MMC, SIP assures good quality of building design specifications. Thus SIP construction can deliver the fabric energy efficiency target with highly insulating and airtight levels or at least meets the minimum standard set in the Building Regulations.

However, there is likely a resistance to promote SIP as part of MMC in house building sector. This comes from lack of understanding and reluctance to innovate (e.g. applying CAD/CAM, utilising building performance and energy simulation tools), skepticism towards MMC and lightweight building construction. These issues should be addressed through trainings, developing methodical and organisational skills for operative engineers. Besides, successful demonstration projects promoting MMC and SIP will

give confidence for designers and house builders to work together to deliver good quality and affordable homes and towards building zero carbon homes by 2016. Indeed, it is very rare to find short-term or long term monitoring of a SIP building envelope yet to allow being fully assessed. This issue is addressed in the research work through presenting a detailed field performance data of SIP construction units, including thermal performance, issues related to thermal bridging and other as-built effects on thermal performance coupled to lack of ventilation potential leading to overheating risk.