Introduction
The United Kingdom has established the target of the “Climate Change Act” which aims to reduce CO2 by 80% by 2050 (Committee on Climate Change, n.d.). In order to meet this target, dwellings in all over the UK should emit as less carbon as possible. Demolishing the existing houses is not a preferable procedure, as instead of the huge waste of materials, the cost of new constructions is very high. Therefore, retrofitting dwellings seems to be the best option in terms of minimizing the energy demand and the investment. This work is divided into two parts that investigate a quite old terrace dwelling (Figure 1) which is located in Wales. The first one is the SAP rating and the second is the carbon footprint.
Figure 1. Front aspect of the house.
Part 1 – SAP rating
According to SAP (2012), SAP is the Standard Assessment Procedure and it is a tool to calculate the energy performance of the UK dwellings. More specifically, SAP rating is determined by the energy costs of the space and water heating, ventilation and lighting. The SAP rating has a scale of 1 to 100, and buildings with higher SAP have lower annual fuel costs. The house that will be investigated has a SAP rating of 39.1 and the target is to both increase this score as more as possible and decrease the total energy cost. Additionally, it is crucial to mention the fact that the SAP rating is independent of the household size, the ownership and efficiency of the electrical appliances, and the individual heating patterns and temperatures (SAP, 2012). However, its aim is to improve the fabric, ventilation, hot water heating, heating system and renewable systems.
Fabric
External walls
Our first priority is to insulate the external walls, as they are 350mm stone solid walls with no insulation, resulting in a U-value of 2.3 W/m2K. Therefore, heat losses through the external walls are significantly high, meaning that they should be insulated. In this particular case, since there are no planning constraints, the chosen insulation will be placed externally. The main reasons for external wall insulation are:
” No loss of room, as external insulation does not decrease the internal area of the building.
” No disruption of the occupants during the placement of the insulation.
” Minimize the damp penetration, as the whole insulation construction will act as an obstacle to the water by stopping its transfer inside the building.
One quite challenging step is the decision of a proper insulation material. The chosen material is cork insulation for a number of reasons (Greenspec, n.d. and Thermacork, n.d.):
” 100% natural and manufactured from renewable resources
” Waterproof
” Recyclable
” Low embodied energy
” Good insulating properties
The company that will provide the wall insulation is Mike Wye & Associates which is located in Beaworthy, UK. Their cork product is the Secilvit cork board insulation (Secil Argamassas, 2012) and their whole insulation system is shown in Figure 2.
Figure 2. The external wall insulation system (Secil Argamassas, 2012)
The thermal resistance of this particular cork board is 2,5 m2K/W when the thickness is 100mm. Due to the lack of information of the investigated dwelling we have to assume that, since the wall U-value is 2.3, the actual stone wall has a thickness of 0.33mm and a thermal conductivity of 0.84 W/(mK). Additionally, we assume plaster of 0.02 plaster with 0.4 W/(mK) of thermal conductivity. Therefore, calculating the final U-value is now possible:
The external wall insulation will not be applied to the party walls, as they do not have contact with the outside temperature. Therefore, the actual wall area for insulation is:
The amended values in the SAP excel file are shown Annex A. It is crucial to mention that the U-value of the party walls is 0, according to SAP (2012).
The cost of the cork insulation system is shown in Figure 3.
Figure 3. External walls insulation cost. Prices can be found in the company’s website (Mike Wye & Associates (2018). Excluding VAT.
Floor
The existing ground floor does not have any insulation, therefore insulating it could result in even fewer heat losses. The insulation material should be rockwool and more specifically, Rockfloor product from Rockwool company (Rockwool, n.d.). The existing floor has a U-Value of 1.2 W/m2K, thus its thermal resistance is approximately 0.83 m2K/W. Rockwool floor insulation will be 100 mm thick resulting in a thermal resistance of 2.6 m2K/W. The amended U-Value should be:
The values that were altered in the excel for the floor insulation are shown in Annex B.
As far as the cost is concerned, Figure 4 shows the required materials and their cost, according to Rockwool (2018), Tile Mountain (n.d.) and Wickes (n.d.).
Figure 4. Floor insulation cost.
Roof
The roof has 50mm insulation between the joists which is translated to a U-Value of 0.68 W/m2K. This thermal performance is not the ideal one, therefore we should add a 220mm loft insulation of Rockwool, which has a thermal conductivity of 0.044 W/mK (Rockwool, n.d.). The thermal resistance of the Rockwool and the existing insulation is 5 and 1.47 m2K/W respectively. Therefore, the amended U-Value of the roof should be 0.15 W/m2K. The cost of the roof upgrade is about 620 £ incl. VAT (Rockwool, 2018). The amended values in the SAP excel file are shown Annex C.
Windows
Windows in the dwelling are double glazed, however, they are quite old resulting in a U-Value of 3.1 W/m2K. Therefore, the windows should be replaced with new ones that will have a better thermal performance. Installing double glazed windows with U-value of 1.4 W/m2K will have more than 50% better performance (Iorweth H. et al., 2013). Also, the use of curtains of a 0.16 m2K/W thermal resistance will result in a U-Value of 1.15 W/m2K (CIBSE, 2016). The total price of the windows will be approximately 4,900 £ (Iorweth H. et al., 2013). Annex D shows the alterations in the excel file.
Doors
Existing doors have low thermal performance as well, meaning that their replacement could be ideal. Thus, instead of the U-Value of 3.1 W/m2K, we can install doors with U-Value of 1.8 W/m2K so as to minimize heat losses as much as possible. The cost of the doors will be about 563£ (B&Q, n.d.). Annex E includes all the changes in the excel file.
Thermal bridging
Thermal bridging usually occurs at the junctions between plane building elements, such as roof, wall, openings and in general where there is no continuity of the insulation. The existing thermal bridging has been calculated using the equation HTB =yΣAexp and the y factor used is the typical one of 0.15. Thus, there is no information about the construction and the only clue is that the dwelling is a pre-1919 one. In order to determine the thermal bridging of the house after the retrofit, the SAP document states that the proper equation is HTB =Σ (L*Ψ). However, the Ψ value differs from junction to junction and its calculation occurs from the detailed analysis shown by Ward T. et al. (2016). Typically, thermal bridging is determined using proper software because of its complexity. Therefore, in this document, due to the lack of software and detailed information (e.g. dimensions), we assume that the thermal bridging will remain the same even if it will improve by using insulation.
Systems
Photovoltaics
The installation of renewable energies is of paramount importance for the SAP, thus photovoltaics (PVs) will aid achieving even higher rating. The roof area is about 27 m2, meaning that half of the area facing South-West can be used for applying PVs of a total power of 2kW. They are produced by the Ubbink company and they have cell efficiency of up to 17.44% (Buypvdirect, n.d.). Along with the solar panels, a whole system is needed (full kit) that includes products such as the inverter and specific wires. However, it is crucial to install a battery as well so as to store possible excess of energy (mainly, during summer). Therefore, the PowerFlow Sundial 2.0kW was selected (The Renewable Energy Hub, n.d.). The total cost (excl. Delivery, installation and VAT) is shown in the table below. The amended values in the SAP excel file are shown Annex F and the calculations to determine PVs energy are in Annex G.
Solar thermal heating
Unfortunately, the roof does not have enough space for the installation of both the PVs and the solar thermal heating. However, the dwelling has a relatively new mains gas combi boiler (up to 90% efficiency), therefore the water heating method is still reliable.
Lighting
According to SAP (2012), the calculation of lighting depends on the number of low-energy outlets and the overall daylighting, which does not change. In terms of the outlets, all the 14 outlets are low-energy, thus there is no room for improvement in lighting.
Final cost
The cost of each improvement is shown in the table below.
According to Gov.uk (n.d.) and Construction Laborer Salary (2018), the average construction laborer salary per hour is approximately 8£. However, insulation installation may require people with expertise in this particular field, therefore we expect to have even more labour cost. Additionally, the VAT for labours is 20% and the VAT for the building materials is 5%, because they are energy efficient materials (Gov.uk, n.d.). Therefore, the approximate final cost with VAT and delivery but without installation is as shown below.
Results
The final results of the retrofit are shown in Figure 5. The initial total energy cost was 1242£, whereas the final energy cost is 99£, thus there is a 92% reduction in the costs. Also, the amount of money spent will not be more than 20,000£ (incl. installation), meaning that we will spend less than 70% of the budget. Additionally, the SAP rating will be 56% higher, from 39.1 to 95.1. The results of the SAP rating of each improvement compared to their costs are shown in Figure 6.
Additionally, not all the alterations can be applied simultaneously. Windows and doors must be installed before the external insulation so as to avoid as many thermal bridges as possible. Roof and floor insulation can be applied at the same time with no problem at all. Lastly, the PVs should be placed after the external wall insulation as well, as the workers will need space and minimal obstructions by the wall insulation – workers.
Figure 5. Overall performance.
Figure 6. SAP improvements in relation to costs.
Part 2 – Carbon footprint
According to the Parliamentary Office of Science and Technology (2006), “a carbon footprint is the total amount of CO2 and other greenhouse gases, emitted over the full life cycle of a process or product”. However, the calculation of the complete life cycle can be proved to be challenging, as not all its stages are easy to comprehend and determine, such as the end-of-life management (Parliamentary Office of Science and Technology, 2011). Nowadays, the measurement of the carbon footprint is becoming more and more popular because of the whole world’s attempt to reduce carbon. For instance, Europe is planning the “2030 Climate & Energy Framework” and the United Kingdom established the “Climate Change Act” to reduce CO2 by 80% by 2050 (Climate Action – European Commission, 2018 and Committee on Climate Change, n.d.).
Hammond G. and Jones C. (2011) state that the percentage of carbon emissions that the buildings are responsible for is equivalent to the 40% of the total worldwide emissions. Thus, the effort on analyzing the whole life cycle of the buildings could be of paramount importance in order to understand how to manage and reduce the carbon emitted from buildings as a whole. A reliable way to calculate and evaluate all the materials of a construction is the use of the Construction Carbon Calculator (CCC) of the Environmental Agency of the (UK Gov.uk, 2015). Therefore, in this report, two different wall insulation materials will be analyzed with the CCC so as to investigate their carbon footprints. These materials are the cork and the expanded polystyrene insulation (EPS).
Cork insulation
The first step to calculate the cork’s footprint is to identify the total volume of the insulation. The volume depends on the chosen thickness of the material and the total external wall surface. The cork is 100mm thick and the external walls, in which it will be applied, are about 91.6m2. Therefore,
The next step is to determine the cork’s mass, thus the volume and the density of the material are required. According to Mike Wye cork product (Mike Wye & Associates, 2018), the density of the material is 120kg/m3. Therefore,
Additionally, 10% waste of materials should be calculated in order to avoid possible lack. Therefore,
The inventory of carbon and energy (ICE) states that the embodied carbon of cork is 0.19 tCO2/t (Hammond G. and Jones C., 2011). The final step is to register these data in the CCC so as to calculate the final carbon footprint of the cork material. However, it is crucial to know the distance between the factory and the site. The cork factory is located in Maceira (Portugal), meaning that the product will travel to the closest port and ship to the site which is in the South Wales valleys (Secil Argamassas, n.d.). Thus, the shipping via road is about 400 miles and the shipping via sea is 800 miles. The results from the CCC are shown in Figure 7.
Figure 7. Carbon footprint analysis of the cork insulation.
EPS insulation
The other insulation material is the EPS which is a non-sustainable material. The calculations for its carbon footprint are:
The EPS thickness is less than cork’s and that is because EPS insulation is more effective, and less material is required for the insulation of the building. Also, according to Knauf technical specifications (Knauf Insulation, 2011), the density of the EPS is 15kg/m3. Knauf’s factory in the UK is located in Sittingbourne, Kent which is 205 miles away from the site (Knauf, n.d.). The comparison, in terms of carbon footprint, between cork and EPS insulation is shown in Figure 8.
Figure 8. Carbon footprints of both the insulation materials.
The results are quite interesting, as the cork produces 39% less carbon emissions even if it is imported from another country. The major difference is in the embodied footprint, as cork has approximately 50% less and this is because cork is a sustainable material, whereas EPS is basically a plastic material. In terms of transportation, cork emits about 45% more CO2 but the amount of carbon emissions in transportation is not high enough to alter the overall carbon footprint.
Conclusion
In order to achieve low carbon emissions, a retrofit can be quite challenging. In this particular case, all the used materials are sustainable ones, meaning that they produce as less CO2 as possible. The importance of the selection of the materials is obvious through the Part 2 of this report.
Finally, the investigated dwelling will have a SAP rating of 95.1, thus it is even higher than the 2050 target, which needs rating above 92 (Iorweth H. et al., 2013). At the same time, the energy costs are less than 100£ and the carbon emissions will be decreased to more than 90%.