Part 1: ‘Achieving the TER and TFEE Rate’. First, the TER: (see related articles for parts 2-5).
Most developers are now familiar with the idea of meeting the Target Emission Rate (TER). This figure is based on your actual dwelling, but with notional specification and factors instead of the details you are proposing.
Providing your specification means the house is designed to create less carbon emissions than the notional calculation, you can show compliance with this mandatory section of Part L.
How you achieve the TER is up to know – maybe you prefer to take a ‘fabric first’ approach, maybe you prefer to install heat pumps or renewable technology, maybe you prefer an all-round decent specification which includes low U-Values and high efficiencies.
With the current 2010 Part L, there’s no exact science to complying with the Target Emission Rate, which can understandably lead to confusion and frustration.
For the new Part L, the Target calculation is being made simpler and clearer (it may be simpler to understand, but is going to require emission rates which are 6% lower than the current target (8% in Wales)). This clearer specification is called the ‘elemental recipe’.
If you construct your house exactly to this specification, in theory your dwelling will comply with the Target Emission Rate:
U-Values are 0.13 for all heat loss floors and roofs, 0.18 for walls, 1.4 for glazing, 1.2 for semi-glazed doors, 1.0 for solid doors and zero for party walls.
Medium thermal mass (equivalent to a cavity construction) and a thermal bridging value which is better than Accredited Construction Details, but not as good as Enhanced Construction Details.
Heated by a mains gas boiler at 89.5% efficiency with zone controls (in most cases) and weather compensation (in all cases). How water cylinder (where appropriate) with daily heat loss of 1.39 kWh, fully insulated pipework and with a separate thermostat to the boiler.
Air permeability rating of 5, System 1 ventilation and 100% low energy lighting.
For dwellings without mains gas, the Target will be raised to allow developers to use oil or electric heating systems (such as heat pumps) as alternative solutions.
So to confirm, if you match the recipe to the letter, you will comply. You’re unlikely to want to match this recipe to the letter, so that’s where ‘design flexibility’ comes into play.
If you think of the Recipe as a weighing scale, you can get away with not building to the same standard as shown in the Recipe, providing you make improvements elsewhere.
So for example, you could build your wall to a higher U-Value than 0.18, but you’d need to look at improving the heating efficiency and controls to compensate.
Or, you could use a heat recovery ventilation system (System 4) and achieve a lower air permeability than 5 which will improve your score… and in exchange you could use a worse glazing spec or more basic heating controls.
Maybe you’d consider using renewables in exchange for building to a worse specification (but watch out for the TFEE – see next blog).
As you’d expect from Energist UK, our Technical Team will work with you to create a specification which complies with this new Target Emission Rate. If you can’t wait until April, we’ll shortly be offering consultation services using Beta SAP software – call us for details.