RT-2012

Understanding the new rules in France on house construction

As of January 2013 all house builders are facing a new challenge: the RT 2012. There is a lot of confusion about the new rules with everybody having his own interpretation of the law.

maison RT 2012

But most of the basics are not that complicated. This article tries to explain the basics.

About The Law

According to our Minister of “l’Ecologie, de l’Energie, du Développement durable et de la Mer” (Ecology, Energy, Sustainable Development and Sea), the role of the state is to set objectives. The RT 2012 imposes targets, but with a few exceptions, leaves it up to the industry to decide about how to achieve the goals.

The Goal

The goal is to build houses that consume less energy: less than 50kWh/m² annual average. How much is 50kWh? Quite a lot, or not much, depending on how you look at it. It is the energy stored in 5 liters of diesel. If you have a 150m2 house you should be able to heat it with approximately 750 liters of diesel. Your car could drive back and forth to Kazachstan with this amount of energy. For heating a house on the other hand it is not that much: the RT 2012 rules are quite a leap forward in the lowering of energy consumption. But the German ” Passivaus” requirements are even stricter: a Passivhaus can use only 15kWh/m² annual.

50kWh/m² Is Always 50kWh/m²?

No, it is not. The 50-rule is a little more complicated than just 50kWh/m², it all depends on a few factors. It depends on:

  • the type of building
  • the size of the building
  • the region where you build
  • the height of the terrain (lowlands, mountains)
  • the type of heating (electric versus fossil fuels)

The Magic Formula

In order to calculate the exact amount of energy Cepmax your new house is allowed to consume, there is a magic formula:

Cepmax = 50 x Mctype x (Mcgéo + Mcalt + Mcsurf + McGES) where:

  • Cepmax is the amount of energy your house will be allowed to consume in kWh.
  • Mctype is the type of building. For normal living houses this is a factor between 1.0 and 1.2. For some reason office buildings are allowed to use more energy and the Mctype can go up to 2.2.
  • rt-2012 zones-climatiques-franceMcgéo is the geographical area where you are going to build. France has been divided into eight areas (H1a, H1b, H1c, H2a, H2b, H2c, H2d, H3) with each area having it’s own factor. As a result you will be allowed to use more energy to heat your house in Mulhouse compared to when you are in Montpellier. Still, in Mulhouse you will need more insulation than in Montpellier.
  • Mcalt is the height into the mountains of your building plot. The formula distinguishes between three altitude ranges: 0-400 meters, 400-800 meters, and 800 and above.
  • Mcsurf s the surface of your house. Smaller houses are allowed a higher energy consumption than bigger houses. The bigger the house, the more energy efficient it should be. The RT 2012 distinguishes the following size ranges: less than 120m2, 120-200m2, and bigger than 200m2. For apartment the categories are slightly different but the basic idea remains the same: bigger means higher requirements.
  • McGES is a confusing factor. For most houses this factor is 0, but for houses that are heated with wood burners this factor is 0.3 while for houses that are heated by central city heating this factor is somewhere in between.

Are We Done Now?

Almost, two more things to explain. First of all there is electrical heating. If you heat your house with electricity (instead of fossil fuels) you are allowed to multiply the result with 2,58. Not that it will make any difference for the energy consumption of your house. The reasoning is: to generate 1kWh of electrical energy you will need 2.58 kWh of fossil fuels. For you as the home owner it is of no consequence, you will still only be allowed to use the 1kWh, not the 2.58kWh.

Two Other Parameters

And then there is another snag. The RT 2012 is not only about the magic formula above and the 50kWh/m² (or what other Cepmax comes out of the magic formula), there are two more formulas. One is about the Bbio, the other is about the Tic.

I will explain them in another article.