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.