Building regulations - new domestic buildings - modelling of proposed energy improvements: research report

Research to identify potential improvements in energy and emissions performance for new domestic buildings. Produced in support of proposed improvements to energy standards for new buildings within Scottish building regulations in 2021.

Appendix A: Cost Breakdown

248. The developed costs are based on the expert view of Currie & Brown's cost specialists, drawing on evidence from their internal cost datasets, recent published cost data and information provided by suppliers.

249. The cost analysis is intended to reflect typical national costs from Q1 2020 that might be incurred by a small/medium sized housebuilder using timber framed construction methods and with a reasonably efficient supply chain, design development and construction processes. However, costs incurred by individual organisations will vary according to their procurement strategies, the location of their activity (e.g. costs will be higher in more remote locations such as the Western Isles than in the Central Belt) and the detail of their housing product. These variations design, location and delivery method could result in a cost range of +/- c.30% or more (see Section 5). Notwithstanding these variations, the proportional uplifts associated with moving from one specification to another are likely to be relatively similar across different market segments[36].

250. To provide context to the cost variations assessed in the study an indicative overall build cost (£ per m2) for each building archetype was estimated using Currie & Brown internal data. This figure is indicative of the level of cost that might be expected for a home built in accordance with the requirements of Section 6 2015. The build cost should be taken as indicative only as it is sensitive to a wide range of design and specification variables in addition to the economies of scale and regional variations discussed previously.

251. Base costs for future years are those for the 2020 price year, and subject to adjustments for learning for technologies that have not yet reached a mature market position. It should be noted that construction costs can vary considerably and rapidly with market conditions, particularly where activity levels result in a change in the availability of skills and materials. In these situations, it is not unusual to see quite large (several percentage points) change in overall costs over a period of months.

252. Table A.1 includes details of the cost information used for each specification option, including any variations between building type, costs are only shown for those specifications that vary between the considered specification options.

Table A.1 Cost data for fabric elements that vary between the selected specifications
Element Specification Unit New cost
(£ per unit)
Annual maintenance costs (£ per unit)* Average life expectancy
External Wall – insulated plasterboard (30-60mm insulation), timber frame (120mm PIR insulation between studs), cavity and brick cladding 0.17 W/m².K £187 £0 60
0.15 W/m².K £192 £0 60
0.13 W/m².K £196 £0 60
Ground / Exposed Floor (concrete slab, rigid insulation and screed) 0.15 W/m².K £91 £0 60
0.12 W/m².K £100 £0 60
0.10 W/m².K £100 £0 60
Roof – mineral wool insulation between and above joists 0.11 W/m².K £216 £0 60
0.09 W/m².K £208 £0 60
Windows uPVC 1.4 W/m².K £395 £0 30
1.2 £335 £0 30
0.8 £285 £0 30
Doors composite 1.4 W/m².K Nr £700 £0 30
1.2 Nr £800 £0 30
0.8 Nr £950 £0 30
Gas boiler (incl flue, pump and controls) System boiler Nr £700 £100 15
Combi boiler Nr £800 £100 15
ASHP Standard (no cylinder) Nr £3,500 £75 15
Higher efficiency (integrated cylinder) Nr £6,500 £75 15
Hot water cylinder 150l standard Nr £750 £0 20
200l standard Nr £800 £0 20
150l for heat pump Nr £880 £0 20
Waste-Water Heat Recovery Vertical pipe system (houses and upper floor flats) Nr £400 £0 60
Tray system (ground floor flats) Nr £1200 £0 20
Radiators (excluding heating pipework and valves) Standard Nr £60 £0 20
Sized for lower temperature heating Nr £90 £0 20
Extract fans 3 in large flats, 4 in semi /mid terraced and detached homes Nr £450-600 £0 20
MVHR unit No ductwork Nr £1400 £30 20
MVHR ducting Rigid ductwork m2 GIFA £15-20 £0 60
Roof mounted - photovoltaic panels Fixed costs for systems <4kWp Per installation £1,100 £48 25
Variable costs for systems <4kWp Per kWp installed £800 Incl in fixed 25
Variable costs for systems >4kWp Per kWp installed £1,100 £12 25

Cost projections

253. Cost projections were assigned to each specification option to capture any expected change in the current cost over time. For many building elements no adjustment was applied to the current costs because the technology is deemed mature and unlikely to experience a significant reduction in cost per unit of performance. This does not mean that cost in the future will be unchanged, only that it is not projected to change in a manner that is disproportionate to the wider construction cost base.

254. For more immature specifications, the potential for future reductions in cost through

learning was assessed based on existing published cost projections or by applying appropriate learning rates to global market projections.

255. Figure A.1 shows the future cost projections of technologies relevant to this consultation. These cost projections are relative to 2019 costs and do not account for other economic and market factors that will impact costs over this period (e.g. market conditions, interest and exchange rates, skills availability and commodity prices).

Figure A.1 Projected variation in base costs as a result of learning

Graph showing an example of how the cost of three elements is predicted to reduce as they become more commonly specified within new homes. Triple glazed window costs are predicted to reduce in cost by around 10% by 2030. Waste water heat recover is predicted to reduce in cost by around 25% by 2030. Photovoltaic panels are predicted to reduce in cost by just over 40% by 2030 the reduce further at a slower rate to around 50% by 2050.

256. The analysis does not include any medium to long term cost savings associated with productivity gains of the sort envisaged by the Construction Sector Deal and the Construction Strategy 2025. Should these savings be realised, then this would have the effect of reducing build costs and the additional costs of more energy efficient and lower-carbon buildings, making the achievement of tighter standards more cost-effective. Further analysis of the relationship between build standards and construction productivity is ongoing.



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