Cutting the energy consumption of collective housing

hlm.jpgLast night Arte, a Franco-German TV network, broadcast a documentary on two buildings in Karlsruhe, Germany, which comprise 64 apartments for low income people.

The goal of this show was to demonstrate that energy efficiency and renewable energies can be implemented quite easily to collective housings.

A very important thing was that the costs couldn’t be supported by the tenants but solely by the administration of the buildings. An impossible mission ?

Situation before the works.

The buildings were constructed in the 1960s, a period of cheap energy and when climate change wasn’t a major preoccupation. Thus, the walls were thin and windows single glazed. The energy consumption was hence tremendous for a quasi non-existent comfort inside.

Tenants had the impression of the heat living the flat to warm up the outside while the temperatures inside remained quite low, and thus even with the radiators giving their maximum.

oil_well.jpgOn top of that, the energy source was originally natural gas, which prices had nearly doubled in two years. Natural gas prices are indexed on oil prices, which have been increasing steadily for the past years.

Indeed, a barrel of oil in 1999 costed nearly 10 USD, when as I write those lines, the barrel costs more than 80 USD.

To go further on the topic of oil prices, and according to the International Energy Agency, the prices of this fuel are more likely to remain at those levels or to go up. (cf. IEA expects oil crunch worldwide ; dated July 10th ).

To another source, the peak of oil production is quite near (cf. Peak oil is near… around 2015 ! ; dated May 16th)

This is a huge problem as those costs were to be paid by the tenants who mostly have low incomes and couldn’t stand anymore their heating bills to go up and up.

Moreover, relying to this energy source is also problematic as it has to be imported from Russia or the Middle East and as it emits quite important amounts of carbon dioxide.

Insulation of the buildings and change of heating system.

pellets.jpgRegarding the insulation, it was done by using outer insulating materials in order to keep the surface of the apartments. On top of that, all windows were replaced by double glazing windows.

All this enabled both buildings to need slightly less than half energy as before.

Moreover, the promotion of energy efficient behaviours cut by an additional 15 percent (approximately) the heating costs.

As a conclusion, the energy now needed was nearly cut by a factor three. This made it possible to use a renewable energy source to heat the 64 flats.

Wood pellets were chosen and a new highly efficient boiler was installed. The new system is so efficient that it can generates some electricity which can be used by the tenants or sold to the grid.

Cost of the operation and financial aspects.

euros.jpgOf course, all these works had a cost. The total with the insulation of both walls and windows and the new performing heating system is of 1.5 million € (2.1 million USD).

This makes an investment of 23,437 € (33,240 USD) per housing .

All this will be paid back in 20 years, which makes the investment be of 1571 € (2,217 USD) per annum per flat.

What’s really good about all this is that no costs will be supported by the tenants. The increase of the rent is counterbalanced by the decrease of the heating costs. The 64 families hence don’t pay more after all the insulation works than before.

The owners of the building will pay back their investment in the same period, which is a profitable business as they believe these investments to have a life period of 35 years and they contracted a state-helped loan on the same period to finance these works.


This documentary showed that energy efficiency and renewable energy sources can be implemented in buildings regarded as HLM in France.

HLM, or Habitation à loyer modéré (French for “housing at moderated rents”) are widespread as there are more than four millions of these residences in France.

All this represents accommodation for nearly 14 million people in France, a country populated by nearly 64 million people. (source Wikipedia)

This documentary was thus important as decreasing in an important way both energy consumption and greenhouse gases emissions of those constructions is a vital point for both the local economy and the environment.

The show demonstrated that not only it is feasible, but also that such works are interesting in both regards.

Please note that during the writing of my Master’s thesis, I used a similar case that corroborates the interest of wood energy to heat collective housings. If you are interested, don’t hesitate to state it and I will write an article on it.

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  1. Pingback: Energy precarity hits a fifth of the French population - CleanTechies

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