Thursday 03 November 2016



These constructions that preserve the future…
When building one’s house, the energy factor needs to be taken into account, more so now than ever. In fact from 1 January, the passive house will be the new standard for construction in Luxembourg, two years ahead of all the other European countries. But what is meant by a passive house? The full details with Sophie Brouwers, technical manager with CLK Constructions.

Mrs Brouwers, how would you define passive construction?
Building a passive house above all means building a house that is pleasant to live in; comfortable because it is warm, free of drafts, as in a cocoon; cheap to run, with very low energy costs; and, finally, correctly oriented, to derive maximum benefit from the sun when one needs it most, in winter, and for coolness in summer. In order to achieve this result, it is necessary to call extensively upon experts from the design stage of the plans for one’s future house. This involves planning ahead to the maximum extent possible.

What is the first element to consider?
The building must integrate well within its environment, it must benefit from the relief and the orientation of the land plot. But it is just as important to adapt to everyone’s individual needs for the internal layout of the dwelling. This therefore involves creating the best compromise between the functionality of the rooms and the orientation of the land. The architect consequently has a key role to play in its design.

One often refers to ecology in construction. A house that is designed in order to have the lowest possible level of pollution during the construction phase and then during occupation. What are your views on this?
Yes, this is a fashionable subject. The passive house is already part of this type of initiative due to its low level of pollution generated in the occupation phase. Our dwellings account for a significant part of local energy – geothermal science, heat pumps, solar energy, etc. Personally I like these sources of energy, because they easily enable one to be completely detached from the gas/oil network, on which we depend heavily in the world economy. A few photovoltaic panels, a few batteries (whose market is growing strongly), and you have a self-sufficient house.

And concerning the construction phase?
I always recommend that our clients should pay particular attention to the windows. There are a considerable range of different qualities available and there is no comparison between them. While the glazing is indeed important, the frame that surrounds it is even more important. In fact the frame can be as much as twice as insulating as the glazing itself. And when we know that a window is between 5 and 10 times less insulating than a wall, that certainly gives pause for thought. One might imagine that triple glazing could compensate for shortcomings in the frame. But this does not take into account the fact that the sun’s warmth no longer passes when the glazing is too well-insulated. That means that we lose both ways. The air seal on the frame fittings is also a crucial point for the success of a passive house. Three sealing joints on the window frame are certainly not too many.

In terms of insulating materials, what do you recommend?
At the risk of appearing to be against the general trend, I think that insulating facades still have a bright future. They combine the advantages of their components: a very robust concrete wall and extremely efficient insulation mean that the thickness of a wall can be reduced. In addition, contrary to preconceived ideas on the subject, studies carried out by the Centre Scientifique et Technique de la Construction demonstrate that for an identical energy performance, it is the expanded polystyrene wall that has the smallest impact on the environment. The impact on the environment is less, both from the point of view of production and end of life. This is one of those rare studies that does not stop at the analysis of the material itself, but also incorporates the fixing and construction method. When we know the number of kilometres of adhesive tape used in some houses, one realises just how significant this is.

A passive house respects three fundamental principles: proper orientation, ventilation, and insulation. Which is the most important aspect for a sense of well-being?
These three aspects are certainly very important for a sense of well-being inside the house, but there is another parameter that is all too easily forgotten, namely: inertia. The management of heat must be studied with particular care so that the temperature is neither too high in summer, or too low in winter. It is always pleasant when the temperature is the same in every room.
In order to achieve this, the house must be well enveloped, thermal bridges avoided, but there must also be a good level of inertia with the materials used. I like to bear in mind why it is that we are so fond of the old stone houses: their significant mass retains the coolness in summer and warmth in winter. Our modern houses need to retain sufficient mass in order to even out the
temperature fluctuations experienced in our regions.

What is the most suitable mode of heating?
The heat/air pump offers a good quality/price ratio and only requires light maintenance. Its production capacity is suitable for passive houses. Some clients opt for boreholes and solar panels, which are also good choices. Low-temperature under-floor heating almost goes hand-in-hand with these.
The most advanced technologies these days optimise as far as possible a good number of parameters, such as the internal temperature, and remote control and regulation of the heating system by smartphone. The connected house is also becoming a normal part of life and also enables some energy savings.

How can we tell if a house is a really a passive house?
A passive house respects the insulation levels provided for in the energy passport and is verified for its air tightness after construction. The house is pressurised and the seal measured by an expert assessor. In order to avoid confusion with the energy passport created at the time of the building permit and the energy passport issued for the construction as implemented, the government has modified the regulations. As from 1 October 2016, a stamp will be added to the energy passport to indicate that it has indeed been built as indicated.

Passive construction for everyone – will this make a difference?
The current minimum standard according to the regulations is the low energy house. A passive house consists of a little more insulation and air tightness. For now, the slight additional cost for the insulation is largely compensated by subsidies, which is why almost all our clients opt for passive construction. For CLK, this will not therefore mean much of a change, as we have been building this way for some years now. All our trades are trained and have the necessary skills for this.
For the client, a passive house represents a double advantage: not only reduced running costs, but also a genuine added value when it comes to resale.

Author: Emilie di Vincenzo