Get a Quote

Cooking up a Target Recipe

Currently, if you’re building a new dwelling you need to make sure the heat loss elements meet the following U-Values: 0.25 for floors, 0.30 for walls, 0.00 for party walls, 0.20 for roofs and 2.00 for windows, roof-lights and external doors. The maximum air test result is still 10 for single plots and 8 for multiples. (To clarify, this isn't enough by itself to comply with the current Target Emission Rate, but lists the maximum any one element can be).

There was talk of these U-Values tumbling when the new Part L was released to bring England more in line with the current Scottish requirements, but nope… the U-Values being taken into 2013 regulations will be the same as they are currently.

However, the way the Part L targets are calculated is changing, so this means you could build to these U-Values, but you’re not going to be anywhere near complying!

One of the changes is the introduction of a Target Fabric Energy Efficiency (blog to follow). Another change is to how the Target Emission Rate (TER) is calculated.

Back in 2001, when the TER is first introduced, developers were given a set of details (U-Values, heating efficiencies etc) which would show compliance with the Part L of the time. The 2006 target was created by knocking 20% off these details, and the 2010 target was created by knocking a further 25% of that.

Instead of continuing to use this 2001 specification to create our targets, the specification has been redesigned from scratch for 2013 – this is what’s called the ‘elemental recipe’.

This system has been used in Scotland for a few years now – the rule of thumb is that you can show compliance just by building to the elemental recipe.

So instead of using the limiting U-Values (as mentioned above), it’s recommended you construct new homes to this standard: 0.13 for floors, 0.18 for walls, 0.00 for party walls, 0.13 for roofs and 1.40 for windows, external doors and rooflights.

The air test in the recipe is set to five, the recipe also uses System 1 ventilation and an 89.5% mains gas combi for heating. (There will be adjustments made for houses with oil, LPG or electric heating).

You may spot a few potential hurdles in this recipe… an external wall U-Value of 0.18 will be an eye-watering target for many.

Using a brick and block wall with mineral wool, you’d be looking at around 180mm of insulation to reach a figure like that. If you use PU foam board insulation, you’d need around 90mm of insulation… so this all points to wider cavities.

But before you hang up your set square and apply to the nearest travelling circus, all is not lost! If you look at the different ingredients of the elemental recipe as a see-saw, you can take away from some ingredients, providing you make up for it elsewhere.

So for example, you could build your wall to a maximum 0.30 U-Value, but then you’d need to improve roof insulation (to say 0.09) and switch to triple glazing (with a U-Value of 1.00).

You don’t necessarily need to look at building fabric alone, you could build to a ‘worse’ standard than the recipe (providing you meet the TFEE – see other blog) and then consider some of the following changes / improvements to re-balance the ingredients.

- Use better thermal bridging details (such as Enhanced Construction Details or APA Details).

- A more efficient ventilation system and air leakage result.

- More efficient boilers and heating controls , or the use of low carbon heating options.

- Introducing flue gas or waste water heat recovery.

- Introducing solar thermal or photovoltaic panels.

In order to comply with Part L 2013, you need to make sure both the TER and TFEE targets are met.

Jon Ponting

Author: Jon Ponting

This article was published by Jon Ponting on 09.10.2013.