Friday, 8 November 2019

Options, Options - The Building Regulations Review & the Notional House

I have read commentary in recent weeks on the 2020 Building Regulations Review that suggests an alarming level of ignorance about the way the building regulations work.  It would be a real shame if the organisations behind these comments were to base their response to the consultation on such a fundamental misunderstanding.

The government consultation is proposing two options for new 2020 building regulations - one that it estimates would deliver a 20% reduction in carbon emissions compared to current regulations and another expected to deliver a 30% reduction.

So you would expect that groups interested in energy efficiency would support the second option - producing a 30% reduction.  But no, some seem to prefer Option 1, because they wrongly think it will result in homes with higher levels of thermal insulation.

It won't.

Let me explain.

The Building Regulations for Energy - How it Works

To comply with the Building Regulations for energy efficiency, housebuilders must use a calculation called the Standard Assessment Procedure (SAP) to demonstrate that the house they plan to build will meet requirements to limit carbon emissions and (new in the upcoming version of building regulations) primary energy consumption and affordable energy bills.

Related article: What is Primary Energy?

Focusing on carbon emissions and primary energy, the way the calculation works is as follows.  (See also the figure above).

1. You decide the geometry of the house you want to build (it's dimensions, shape and openings - number and size of windows and doors)

2. You calculate a Target Emissions Rate (TER) and Target Primary Energy (TPE) for a "Notional House".  The Notional House is the same shape as the actual house you want to build but has a technical specification based on Reference Values defined in Appendix R of SAP.  The Reference Values include insulation performance (U-values) for all the building elements (walls, windows, roof, floor), a maximum allowable amount of openings, as well as air change rates, a heating system and renewable technologies.

3. You then choose the technical specification you actually want to build the house to.  These can differ from the Reference Values - you are free to choose a different heating system, to build to higher or lower insulation levels, to aim for higher or lower air-tightness and whether to include more or less renewable or energy saving measures.  The only constraint is that insulation levels must be higher than so-called backstop values, which are also defined in the regulations.  You calculate the Dwelling Emission Rate (DER) and Dwelling Primary Energy (DPE) based on this house design.

4. So long as the carbon emissions and primary energy for the actual house are lower than the target figures generated by the Notional House, you're good to go, the design is compliant.

This elegant system defines a level of performance for the energy efficiency of new homes while giving developers a free hand in how they want to build.

Option 1 in the consultation sets the Reference Values for the notional house to have highly insulated walls, floor roof  and openings.  The Reference Values given for Option 2 come with slightly lower insulation levels, but add in solar PV and waste water heat recovery to the specification, resulting in lower overall energy use and carbon emissions than Option 1.

Just because Option 1 has higher insulation in the reference values it does not mean that houses will be built with this level of insulation.  As mentioned earlier, developers have complete freedom to choose a specification so long as it meets the target emissions and primary energy levels.  If it is a lower cost option, they are just as likely to reduce the insulation levels and add solar PV to meet Option 1.

If you are interested in lobbying for a 'Fabric First' approach, then you should focus on arguing for more ambitious backstop values for insulation and airtightness, but please don't argue for Option 1 Reference Values.  Option 2 will deliver higher-performing homes and will force housebuilders to push energy efficiency further and faster.  It will also likely result in higher levels of insulation in as-built homes.


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