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Updated Cost Review – Cost of building to the Code for Sustainable Homes

by Mel Starrs on September 4, 2011

in Code for Sustainable Homes

Along with the usual updated quarterly figures for the number of dwellings built to CSH, we had a bonus publication this month – Cost of building to the Code for Sustainable Homes – Updated Cost Review. The report is interesting and I’ll go into deeper analysis below. What I found more interesting was the Andrew Stunnell press release accompanying it:

The new research, based on interviews with developers and the latest information about environmental technologies, shows the overall extra costs of building new homes to standards set in the Code for Sustainable Homes is falling year on year.

For homes built to Code level 3 standards, average extra costs have fallen by almost three quarters in the last three years – falling from £4,458 in 2008 to £1,128 in 2010.

This isn’t actually in the report – to find these figures I thought I would have to dig out the report issued in 2008 but I’ve looked in all the cost reports I have access to and cannot find £4,458 quoted anywhere – can someone enlighten me? I don’t doubt the figures, I just found it odd that the report states it aims as:

•    Consult with the home building industry to gather data on the costs of building Code homes.
•    Gain insight into the extent to which technical solutions for delivering Code homes have become/are becoming standardised.
•    Understand to what extent the costs of building Code homes have changed as experience of building to the Code increases.

The third aim looks at the changes in costs. Chapter 7.2 states:

A cost reconciliation was undertaken comparing costs from the March 2010 report to the current study. Generally it was found that some costs were nominally reduced by approximately 8 per cent (primarily energy and water issues). However, this needs to be weighed against the market conditions. Tender price indices indicate that costs have fallen approximately 11 per cent in the last two years, therefore, the nominal reduction in the energy and water issues may have been attributable to market conditions rather than learning and hence in actual fact, costs may not have changed much. However, there was the general view that costs of low and zero carbon technologies had dropped due to larger volume of procurement.
The general consensus from the consultation was that costs had not dropped significantly and programme times were not shorter (hence, preliminaries costs remained unchanged). However, in terms of learning, the homebuilders did state that processes were smoother and construction methodologies becoming more standardised. Since, it has taken them two years to achieve this level of comfort in building to Code homes, it may be that the next two years will see greater levels of change in learning.

Not exactly the same message, is it? Odd.

Anyway, the report is a mine of useful graphs and most of the messages concur with my own (extensive) experience over the past year (I’ve been dealing with a lot of CSH3* and CSH4* developments, mostly within GLA, mostly driven by HCA funding requirements on social housing in generally flatted developments (but some houses) some of which is with developers who took part in the study).

I have a couple of comments though. Firstly, it seems to have taken quite a while to publish the report – it feels like it was written about 6 months ago, and the research was carried out last summer. Since then the CSH has been updated in November ’10 (mainly to align with Part L 2010) so some of the credit specific costs will have changed. Also it is now harder to reach CSH3* as in effect we have lost the credits awarded in ENE1.

The typical mix of social:private for CSH is 80:20, yet the report is based on private assumptions generally. I would guess that the only developers voluntarily using CSH are those doing CSH5* and CSH6* – everyone else does for either planning or HCA funding (despite CSH being a ‘voluntary’ code). This makes a difference to the analysis which discounted the use of Lifetime Homes and Secured by Design. This skews things slightly, especially the least cost approach – the reality is that there are very very few instances where this would be the norm. However, this could easily have been taken into account – as the majority of the dwellings have to comply with LTH and SBD, they can be discounted as extra over costs anyway?

I also have a bone to pick with Table 12, where a ‘good’ specification has an air permeability of 3 and yet uses natural ventilation – good practice would generally dictate MVHR (or another mechanical ventilation) at such a low air tightness. Savings can then be made on trickle vents in the windows. The thermal bridging values also look very optimistic for the advanced specification.

Despite these minor quibbles, the rest of the document concurs with my experience. Generally CSH3* can be met with fabric alone, but perversely where planners demand a 10% renewables obligation, fabric is dropped to make budget for PV (mostly). CSH4* can be met by improving the fabric – more renewables are generally not added roof space runs out for PV. At higher levels, biomass starts to kick in.

Table 16 show the insane costs of the water credits at CSH5* and CSH6*

My two favourite graphs are Figure 2 and Figure 3 – these would have been really useful to me about a year ago. As it stands, they are useful but caveated with the world moving on and my comments above.

Well worth a read and could be handy to refer to.