Cost study

r e o m ad

C = C + C + C + C (7-7)

7.1.2 Cost study

An economic analysis for the base design of SIP dwelling developed from Chapter 5 was compared with a new built masonry construction, of a similar size, representing the traditional construction method dominant in the house building sector. In fact, the housing stock profile derived from EHCS in 2007 showed 15.5 million dwellings with cavity walls (equating to 70% of the housing stock), half of which are insulated (EHCS, 2009).

By selecting a brick/block work with insulation filled cavity, as the new built dwelling meeting the requirements of the Building Regulations (2010 part L1A), the comparison could demonstrate the differences between buildings using a traditional construction method, with heavy weight, and the modern construction method, with lightweight SIPs. For a timber framed dwelling, performance, and cost can lie in between this range as being reasonably cheap and popular, as it is constructed by traditional methods, emits less carbon dioxide compared to masonry dwellings and thermally performs worse than a SIPs building. Masonry constructional information was selected from Table 3.49 – 3.51 in CIBSE guide A (CIBSE, 2006a), which meet the current criteria for new built dwellings as set out in 2010 part L1A.

Due to a lack of information about building onsite, between SIPs used in the project and estimation for a masonry dwelling of the same size, the cost calculation in the study excludes the substructure, only covering material cost, heating and DHW system, replacement cost for building elements and operational cost. Most of the material cost for masonry construction, windows were derived using the Spon's Architects' and Builders' Price Book (Langdon, 2010). The cost of SIPs and VELFAC windows were sourced from the suppliers. The information on heating and DHW, system cost and replacement as well as the lifespan are given in the BS EN 15459:2007.

It was observed that a central heating system (a system with boiler and radiators that distributes heat throughout the dwelling) was the predominant form, representing 87%

155

of the total English housing stock, which equates to 19.3 million dwellings in 2007 (Nowak, 2009). 84% of housing stock uses a central heating system fuelled by gas, as it is generally considered to be a fuel which combines low cost and low CO2 emissions most effectively. In the scope of cost comparison, heating and DHW system were chosen to be fuelled by mains gas, as the masonry dwelling will fail performance requirements for an electric heating/DHW installation. Indeed, heating by electricity has a higher fuel cost and greater emissions than any other alternative fuel even where installation and maintenance costs are lower. In some limited circumstances such as small and well-insulated properties, best practice recommendations would allow electricity heating (EST, 2003b). Whilst if electricity is an obligatory source in several restricted locations for mobile homes, then SIPs construction becomes an obvious choice as it conforms with all high standard performance required for installing electric heating as set out in Good Practice Guide 345: Domestic Heating by Electricity (EST, 2003b). In the case of improved performance in which a masonry dwelling could cope with an electric heating installation, the benefits of energy savings based on the predicted heating demand gap between the two construction methods, a significantly higher cost saving would be predicted compared to the result presented below, because electricity price is much higher than mains gas, approximately three times more expensive.

To enhance comparison between different building geometries and sizes, it is proposed to express the results in Pounds Sterling per square metre of conditioned floor area. The global costs calculation of two different packages of measures: SIPs dwelling denoted as EH and masonry dwelling as SH were conducted. For results sensitivity analysis, different price scenarios were looked at and different interest rates for three levels, for both packages: high, medium, and low. Interest rates were derived from market interest rates, adjusted for inflation (i.e. interest rates offered minus inflation rate). The rates are subject to changing market conditions and differ depending on whether being viewed from the private or societal sector: all kind of taxes (VAT, etc) need to be included in private sectors whilst from societal perspective, these taxes are excluded (ECEEE, 2011).

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156 Table 7-1: Building constructional data

Housing type Building component Identification of constructional information U-value, W/m²K

Wall with filled cavity insulation

105 mm brick, 100 mm PU foam, 100 mm dense concrete

block, 13 mm dense plaster 0.3 75.4 Selected

construction

Insulated to raft level pitched roof

12.5 mm plasterboard, 150 mm mineral wool between rafters and 50 mm over rafters, ventilated airspace, roofing felt, 25 mm ventilated airspace, clay tiles

0.2 43.1 Concrete cast suspended

floor

Vinyl floor covering, 50 mm screed, 150 mm cast concrete and

100mm EPS 0.25 45.95

Insulation filled cavity with effective sealing

13 mm lightweight plaster, 100 mm lightweight concrete block, 25mm air cavity with batten filled with mineral wool, 13 mm lightweight plaster

0.5 37.01 Double glazed windows Low emissivity coating layer on the outside surface of inside

pane to reduce heat loss 2.0 9.94

Entrance door Composite door: aluminium and mineral fibreglass 1.54 1.84 (DCLG, 2010a) Pitched roof Corrugated aluminium, SIPs 150 mm, plasterboard 0.22 43.1

Suspended floor SIPs 150 mm, polystyrene, oak 0.16 45.95 Partition wall Timber studs with rock wool insulation 0.50 37.01 Double glazed windows Low e-coating and argon filled to 93% in the air cavity 1.82 9.94 Entrance door Composite door, extreme low U (Door style SFS 405) 0.9 1.84 Air permeability Tested and certified by BSRIA at 50Pa pressure difference 1.82 m³/m²h -

*The thermal transmittance of a conventional hardwood of 65 – 75 mm thickness entrance door with U-value = 2.5 – 3 W/m²K thus in order to meet the compliance for new built dwelling with U-value less than 1.8 W/m²K, a composite door with was selected.

157 7.1.2.1 Initial investment costs

7.1.2.1.1 Investment costs for building construction Table 7-2: Cost of VELFAC windows

VELFAC 200