WHAT DOES IT COST TO RETROFIT HOMES?

1 WHAT does IT cost TO RETROFIT HOMES? Updating the cost Assumptions for BEIS s Energy Efficiency Modelling April 2017 Jason Palmer, Mary Livingstone, Angela Adams Cambridge Architectural Research 2 Contents Contents .. 2 Executive summary .. 3 Introduction .. 7 Purpose of the study .. 7 Scope of the study .. 8 Methods .. 11 Limitations of the study .. 12 Literature Review .. 14 Introduction .. 14 Findings .. 15 Costs .. 17 Organisations interviewed .. 17 Wall Insulation .. 20 Roof Insulation .. 26 Floor Insulation .. 29 31 Heating .. 34 LEDs .. 38 Draught-proofing .. 40 Conclusions .. 41 Appendix A: Literature Review Supporting Tables.

2 43 Appendix B: Acknowledgements .. 68 Executive summary DECC wishes to update its assumptions about the cost of upgrading the energy efficiency of homes. CAR interviewed organisations carrying out energy improvements to homes, asking how much it actually costs to do the work. We also collected data from retailers about the current cost of energy efficiency measures from insulation to LED lights. This study set out to collect data on the actual cost of 18 measures intended to improve household energy efficiency. From wall and loft insulation to new boilers and double glazing, and from LED lights to draught-stripping, Cambridge Architectural Research compiled robust figures for the cost of carrying out different upgrades.

3 We identified 183 energy efficiency installers, plumbers and electricians, and 20 other organisations including large-scale RETROFIT contractors and housing associations with an interest in energy efficiency. We interviewed 52 of them from around England and Wales by telephone and gathered supplementary information by email where required. Some declined to be interviewed because they did not have cost data, but most of them had experience of more than one of the 18 upgrade measures, and the estimates of costs for more common measures are drawn from experience installing them on thousands of homes. We also carried out a search of published literature about the costs of energy efficiency upgrades, including cost data from websites.

4 We found 15 sources with some information about the cost of improving household energy efficiency. Resource constraints prevented us from carrying out more interviews or more thorough literature searching (for example, using references from overseas). Larger sample sizes for the interviews would make the cost cited here more reliable, especially for more uncommon measures where we identified fewer interviewees. Consequently, these figures should be interpreted as indicative costs. Wall Insulation In total, 23 interviewees provided cost data for installing wall insulation, so there was considerable evidence to draw on. Unsurprisingly, interviewees gave a range of different costs for each of the wall insulation measures.

5 For cavity wall insulation, the range was 5- 6 per square metre of wall, or 480 to 660 for a small semi-detached home (less than 80m2). (Costs exclude VAT throughout.) Solid wall costs were considerably higher, given the additional work involved in installing external wall insulation and rendering on top, or fitting internal insulation, applying plasterboard and redecorating for internal wall insulation. The range of costs for internal wall insulation was 55 to 140 per square metre of wall, or 5,000 to 10,400 for a small semi-, compared to 4 external wall insulation costs from 55to 180per square metre or 7,000 to 9,000 for a small semi.

6 We also gathered costs for insulating party cavity walls: ranging from 25- 30 per square metre or 350 per home . This is broadly consistent with cost data from the literature review, which cited costs ranging from 480 to 1400 per dwelling for cavity wall insulation, 6,800 to 15,000 per home for solid wall insulation, and 300- 350 per home for party cavity wall insulation. (The high estimates from the literature for cavity- and solid-wall insulation are higher than those from installers, which may suggest some reduction in costs over time, since the literature was published.) Loft Insulation Again, many interviewees had hands-on experience of carrying out loft insulation work.

7 Twenty-six of them had done this. Again, they offered a range of costs from 10 to 20 per square metre or 180 to 610 per small semi-detached home for insulation installed at the joists. Differences were sometimes due to different insulation thicknesses, and whether the loft already had some insulation (by far the majority of lofts already have some insulation). Costs for insulation at the rafters were considerably higher, at 20 to 40 per square metre, or 1,900 to 2,500 per small semi-detached home . Data on flat roof insulation was very limited, with only two interviewees providing cost data which suggested costs of 50 to 100 per square metre.

8 Again, this ties in well with literature sources, where the range given is from 185 to 670 for insulation installed at the joists (with one high cost cited for a hard to treat loft, at 2,500). Floor Insulation Insulating the floor of a dwelling is less common. We spoke to five interviewees with experience of insulating suspended timber floors (underneath the floorboards), and three of these provided some cost data. (However, we were unable to interview organisations with experience of insulating solid floors.) For suspended floors, one interviewee suggested 750 per large semi-detached dwelling. Two interviewees provided estimates per square metre, ranging from 1 per square metre for material plus a fixed installation cost of around 550, to 95 per square metre in total.

9 How does this compare to past work from the literature looking at the cost of floor insulation? The figures quoted in the literature for insulating suspended timber floors were considerably higher: 3,500 to 8,300 per dwelling. The literature also provided data on solid floor insulation, ranging from 1,300 to 9,800. Glazing Installing double glazing is a very common energy efficiency upgrade, and we interviewed nine firms with experience of this measure. This means the figures collected are more reliable, and based on a large number of installations. Costs were commonly cited in terms of the cost per 5 window, but were also provided on a per home basis.

10 They came out from 4,800 to 7,000 for a small semi-detached house with uPVC windows. Clearly, there are significant differences in quality between different types of double glazing, and interviewees said the costs for aluminium or timber frames might be up to double the cost of uPVC. It was harder to get reliable cost data for secondary glazing partly because this tends to be a DIY measure, not requiring professional installation. Typical costs were cited at 110 per square metre of glazing. Literature sources provided indicative costs for replacement double glazing, but not the cost of replacing only the panes, or of secondary glazing.