Yesterday the Government launched its Energy Efficiency Strategy, and we were particularly interested to see if any mention was given to the role of SAP, the Government’s energy performance assessment tool.

Hockerton Housing Project takes pride in its low-tech, low-cost approach, and the homes consume 15-25% of the energy used by homes built today. But the Government’s energy efficiency measurement assessment tools (SAP and RdSAP) cannot compute the benefit of homes like ours:

  • SAP cannot cater for our use of passive solar gain as our main heating system
  • Use of thermal mass to reduce heat demand through the year is not recognised (the thermal mass in our homes essentially stores the summer heat and keeps our homes warm in winter)
  • SAP assumes that an element of mass thicker than 100mm has no additional thermal capacity is flawed (SAP2009 Table 1e: Heat capacities for some common constructions), contrary to evidence at HHP.  As long as the mass is well insulated (externally) the full thickness of the mass will be effective as a heat sink.
  • RdSAP does not differentiate between internal and external solid wall insulation, so the benefits of external insulation to “lock in” the mass of the walls, which can then aid summer cooling and winter heating, are not recognised for existing dwellings.
  • SAP assumes that thermally separate conservatories are not present, ignoring two benefits:
  • The sunspace provides sheltering of the dwelling from the external environment, therefore reducing heat losses.
  • The sunspace can be used to harvest passive solar energy which can then be brought into the main dwelling to top-up the heat stored in the thermal mass as required.

All this matters because the Government tells us in the Strategy that it intends to make more policies conditional on energy efficiency.  Access to feed-in tariffs and the renewable heat incentive are already affected, and RdSAP or EPC ratings could also be used to introduce differential council tax or stamp duty.  All this will mean that energy efficiency improvements will be made to meet whatever measure of energy efficiency is applied.  Whilst a policy to drive up the value of energy efficiency in the property market would be very welcome, as this is potentially the simplest way to drive investment in existing homes, this must not be so broad-brush as to drive out innovative approaches and a process for ‘exceptions-handling’ must be incorporated into future policies.

Seeing is believing

On the upside, whatever documents come out of Westminster, here at Hockerton we’re enjoying ‘zero’ energy bills as our investment in additional solar PV starts to pay off and the summer heat stored in our thermal mass continues to keep our homes warm.

If you are interested in homes that are comfortable yet consume only 15-25% of the energy used by homes built today, this time of year is the best time to visit to truly feel the difference.  There are some spaces left on the tour this coming Saturday 17 November so book your place on a tour of Hockerton Housing Project here.

Date posted: November 13, 2012 | Author: | 6 Comments »

Categories: Eco homes Existing Homes New Build

6 responses to “New energy efficiency strategy and the risk to innovation”

  1. Ed Davies says:

    Interesting post.

    One suggestion: perhaps in “this must not be so broad-brush as to drive out innovative approaches” it would be better to replace “broad-brush” with “micro-managed”. The problem is not so much that the rules are too broad but rather that they’re too narrow in how they expect a house to work.

    More substantially, I assume the current “poor” rating of the HHP houses (H, I read somewhere) is because SAP would require the assumption of the use of electric heating in the absence of any heating system deemed acceptable. Do you think the houses could now be built as they are or would building regulation compliance require the addition of an LPG central heating system or the like?

    • HHP says:

      The use of broad-brush was to reflect the utilitarian nature of SAP, it works for most homes, but not minority approaches such as our design – but I agree it could have been better phrased! As for micro-management, we’re not against better oversight of SAP – that’s another story, but it seems foolhardy to place great reliance on a tool that does not require a site visit for the ‘as-built’ assessment…

      On building regulations, we’re keen on devolved decision-making and informed planning officers, and for DCLG and BRE to recognise the benefits of high thermal mass. Unfortunately, without industry backing (and the resources that come with it) it is difficult to get our approach on to their agenda.

  2. Sherlyn says:

    It’s nearly impossible to find well-informed people for this
    topic, however, you sound like you know what you’re talking
    about! Thanks

    • HHP says:

      We do our best to help!! If you have anything you need to know please let us know via the contact button- Simon

  3. Charles S Murphy says:

    I also have significant reservations regarding the DECC Energy Efficiency Strategy, I am questioning its fundamental analysis assumptions regarding the perceived huge energy benefits of windows Solar Gain. Large windows provide us a lot of light but lose more heat than walls; they do not provide us with free and usable energy. I know this statement is so obviously true (almost an ‘elephant in the room’), but UK government and its agencies are so linked into the flawed Solar Gain concept that it will be very difficult to change their views. I am writing a paper on the subject and it will be published soon.

    • HHP says:

      It all depends! With a high mass design and super insulation the windows allow you to heat the property with just passive gains. This reduces overall energy consumption drastically as the energy use data on our houses over the last 17 years clearly demonstrates. Total energy use per house is typically 10kWh per day.

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