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23.3.1 ICE domestic building model

The ICE database (Hammond and Jones, 2008a and 2008b) has been applied to real-world applications. A number of case study buildings were collected from both domestic (Hammond and Jones, 2007) and non-domestic building sectors, not only from the literature-based resources but also utilizing primary case studies. It was not always possible to determine a sufficient specification of the buildings under analysis. However, building specification has profound effects upon results of embodied energy and carbon. Therefore, to enable embodied estimates for bespoke buildings to be determined, an ICE Domestic Building Model was developed. The model operates with the following variable parameters:

■ Building type: detached, semi-detached, terraced, bungalow, or low-rise apartment

■ Fabric reconstruction: a range of predetermined walls, floors, and roofs allow a building to be reconstructed to specified thermal standards

■ Total floor area and height of each floor

■ Window type and area

■ Finishes: floor finishes (carpets, vinyl, laminate, timber floorboards), wall finishes (paint, wallpaper, tiles), and window furnishes (a range of curtains and blinds)

■ Garage (single, double) and driveway (concrete, gravel , brick, tarmac)

■ Housing development impact (connecting roads, pathways, walls, etc.)

■ Conservatory (small, medium, large)

■ Grid electricity carbon coefficient and electricity generation efficiency

The model utilized flow charts, one of which is displayed as a schematic in Fig. 23.4. This flow chart may be used along with appropriate coefficients to estimate the output of the ICE Domestic Building Model. Figure 23.4 depicts the simplified representation of a semi-detached building. In contrast, the full ICE

Fig. 23.4 Schematic of the ICE Domestic Building Model.

Domestic Building Model retains higher detail, ease of use, and dynamic assumptions, although the simplified ICE Flow Charts produce results with good proximity of the full ICE Domestic Building Model. The full model is tied into the generation efficiency and the carbon coefficient of electricity as a variable parameter. To calculate the embodied energy and embodied carbon it is required to run through the flow chart twice, once for embodied energy and once for embodied carbon. Two tables accompany the flow charts (not included in whole herein); 'Table A' contains embodied energy and embodied carbon coefficients for construction elements, such as walls, floors, and roofs and a miscellaneous addition (which accounts for kitchens, bathrooms, and toilets as a function of floor area). A sample of embodied coefficients (from 'Table A') is shown in Table 23.1. These coefficients have been selected for a building that meets the 2006 (Part L) UK building regulations. 'Table B' contains embodied energy and carbon coefficients of extra building features, for example, driveway, garage, conservatory, energy to construct a housing development (i.e., connecting roads and pathways, etc.). 'Table A' is integral and must be applied, whereas 'Table B' is optional but is required to model the impacts of additional features such as a garage, driveway, and conservatory. Application of Table 23.1 to the flowchart (in place of 'Table A') allows an example building to be analyzed. In the case of a 100 m2 semi-detached building with a floor height of 2.5 m and 14 windows (1.2m x 1.2m), for example, the embodied energy was estimated at 533 GJ and embodied carbon at 39.6 tonnes CO2.

Table 23.1 Sample coefficients of embodied energy and embodied carbon.

Embodied energy Construction element (- MJ/m2)

Embodied carbon (-kgCO2/m2)

Ground floor, Gc

781

86.0

Upper floor, Uc

453

23.3

Roof, Rc

554

37.1

Internal wall, Ic

290

26.3

uPVC window, Wc

2,300

112.2

External wall, Ec

782

64.4

Foundations, Fc

867

103.0

Party wall, Pc

483

45.2

Miscellaneous, Mc

350

25.0

Waste, Dc

1,200

76.0

Calibration factor, c.f.

1.3

1.3

23.3.2 Benchmark results

Hammond and Jones (2007) analyzed semi-detached houses and provided benchmark results by building floor area for this single building type only. Results from the ICE Domestic Building Model have been analyzed to create benchmarks of embodied energy and embodied carbon for a broader range of dwelling types. The work has now been extended to include detached and terraced houses, bungalows

(detached), and apartments (three storey blocks and four storey blocks). The results may be used to estimate the embodied impacts of residential buildings by floor area and building type. It is hoped that these results may be used by building professionals to determine a baseline, and therefore offer benchmarks for future carbon mitigation strategies.

The base case buildings were assumed to have a basic building specification. Each property conforms to 2006 UK building regulations with uPVC double-glazed windows. There were no additional features such as garages, driveways, or conservatories. The benchmarks therefore only estimate the embodied energy and carbon of the building itself and include no external additions. They allow the total embodied energy and total embodied carbon to be estimated based on the floor area and property type. Figure 23.5 shows the benchmark results for embodied energy and Fig. 23.6 for embodied carbon in the form of contour charts or plots.

Embodied Energy-GJ

Bungalow-Detached

Apartment-3 Storey Building

Apartment-4 Storey Building

Semi-Detached

\\\\V

V\v\

«

II

Fig. 23.5 Embodied energy guidelines for domestic buildings.

The uncertainty associated with these benchmarks was estimated to be ±30%. Using these charts a detached house of 150 m2 was predicted to have an embodied energy of 800 GJ (see Fig. 23.5) and an embodied carbon of 59 tonnes CO2 (see Fig. 23.6). Likewise a 100 m2 semi-detached property was estimated at 530 GJ and 39.5 tonnes CO2, which is comparable to the previous estimate (from the flow chart). These results may be used to estimate the embodied impacts of average

Detached

Terraced s0

B ungalow-Detached

Apartment-3 Storey Building

Detached

Apartment-4 Storey Building

Semi-Detached

Terraced50 75 100 125 150 175 200 225 250

Floor Area-m2

Fig. 23.6 Embodied carbon guidelines for domestic buildings.

UK dwellings. To do this the average floor area of each building type would be required. For English buildings (UK-wide data are not available) the average floor area of each newly built property type was obtained (ODPM, 2001). The benchmark results were then applied to the average floor areas to determine the typical embodied energy and carbon of each building type. These results are displayed in Table 23.2.

The weighted average embodied energy of a newly built property in the UK was estimated to be 480 GJ and its embodied carbon 36 tonnes CO2 (Table 23.2). Average apartments and terraced properties were estimated to have similar impacts and were the lowest impact options; however, comparatively the terraced building was larger with an additional 18

floor area. An average semi-detached property was estimated to have a 30-35% higher impact than an average terraced or apartment building, but was only 7% larger in floor area than the former. Bungalows were determined to have a particularly high impact per unit floor area, especially in comparison to the alternative options. An average bungalow of 76 m2 was estimated to have an embodied energy only 10% lower than an average detached house of 125 m2, although the latter benefits from a 65% larger floor area. These results demonstrate the importance of both floor area and building type in terms of total embodied energy and carbon. It is interesting to compare these

B ungalow-Detached

Apartment-3 Storey Building

Detached

Apartment-4 Storey Building

Semi-Detached

Terraced50 75 100 125 150 175 200 225 250

Floor Area-m2

Fig. 23.6 Embodied carbon guidelines for domestic buildings.

building types by how well (environmentally) they perform to provide a set floor area. The results from Table 23.2 were therefore normalized to per unit floor area, as are displayed in Table 23.3. The results in Table 23.3 suggest that (detached) bungalows have the largest impact per unit living area and by a fair margin. In the case of a bungalow this was mainly attributed to the property having a single floor at ground level. Such buildings require a larger area of foundations and roofing than any other building type, consequentially resulting in a high embodied energy. Low-rise apartment blocks were, additionally, considered to have a high impact per unit floor area. But there are two other factors working in favor of apartmentstyle buildings. First of all the floor area is defined as the total floor area enclosed by the walls of the property. Low-rise apartment blocks in the UK require a level of communal space, such as stairways or hallways, which is dependent on the size of the building and not included in the floor area of the apartment. However, the embodied energy and carbon were estimated for the entire building and therefore each property takes its share of these burden. This implies that an apartment of area 80 m2 is in effect more 'spacious' than a semi-detached or detached building of the same floor area. While this seems implausible, it is the absence of internal stairways and (possibly) reduced hallways that increases the comparative spaciousness of these properties. Furthermore it can be expected that a property arranged over a single level would utilize space more efficiently than one over multiple levels.

Table 23.2 Embodied energy and carbon of typical newly built English dwellings.

Building type

Percentage of new properties

Average floor area (-m2)

Embodied energy (GJ)

Embodied carbon (tonnes CO2)

Apartment

(three storey building)

Apartment

(four storey building)

Terraced

24 20

50 68

315 330

25

Semi-detached

15

73

410

31

Bungalow (detached)

11

76

620

47

Detached

31

125

690

51

Weighted average

100

83

480

36

The second factor is from the reduced physical footprint of the building. These buildings take up less space, not only of the building, but normally the surrounding landscape. Semi-detached, detached, and bungalows are likely to have their own gardens, driveways, and pathways, they may have a garage and further landscaping. In comparison apartment-style buildings could have communal gardens and perhaps individual garages, although a block of garages is considered to be a more efficient arrangement than the same quantity of separate garages. The combined effect may be to save embodied energy and carbon of these 'external features' whilst offering a more 'spacious' property for the same floor area. That said, low-rise apartment-style buildings which are well spaced apart (not within a single block), and with spacious surroundings (gardens), may negate any expected external works savings. The external works include the impacts from excavation and filling, concrete, walls, paving, kerbs, roads, fences, gates, painting, storm drainage, and other duct works (see Hammond and Jones, 2008a).

Table 23.3 Normalized embodied energy and carbon of typical newly built UK dwellings _by floor area_

Building type

Average floor area (-m2)

Embodied energy (GJ/m2)

Embodied carbon (kgCO2/m2)

Apartment

(three storey building)

50

6.6

(four storey building)

6.3

460

Terraced

68

4.9

370

Semi-detached

73

5.6

425

Bungalow (detached)

76

8.2

620

Detached

125

5.5

410

Weighted average

83

5.8

435

External works were estimated to be within the embodied energy range 1844-2230 MJ/m2 (habitable floor area) and embodied carbon range 135-177 kgCO2/m2. However, with only two data points, it was difficult to estimate the accuracy of such results. In comparison with Table 23.3 external works represent a significant extra impact. When applied to the average semi-detached house the embodied carbon would increase from 425 to 581 kgCO2/m2. Given its floor area of 73 m2, the embodied carbon increases from 31 tonnes CO2 to 42 tonnes kgCO2, representing an increase of over 35%. For a complete and fair analysis, the impact of external works must obviously be considered on a case-by-case basis. However, these results indicate that further analysis of external works would be desirable.

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