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to combine old and new: new floor levels were added to increase the amount of usable floorspace while at the same time maintaining the existing interior elements (oak floors, marble mosaics, historical carpentry, etc.) to the maximum extent possible. This is all being done with the intention of turning the building into a low-energy office building after its transformation.

According to a study of the energy consumption carried out by the design and construction consultancy bureau Daidalos Peutz, the primary energy consumption was initially (i.e. before works) estimated at 400 kW/m²a - which delivers an E-level of 180 and a K level of 110 for the building shell (Daidalos, 2011). To calculate this estimate, the existing building shell as well as a new technical installation for heating, cooling, lighting and sanitary fittings were taken into account. As the original installations are missing - and most likely cannot be adequately simulated in accordance with existing calculation modules - this estimate delivers a lower limit with regard to the original consumption. However, this result does reflect the consumption to be expected if no architectural adaptations were made to the construction. Since this energy consumption does not meet the current energy standard for new-built office buildings in the Brussels metropolitan area, a decrease in the energy consumption was desirable, although such monuments are in principle not subject to this regulation.

As heating was estimated to make up approximately three-quarters of the total energy consumption in the building's initial state, an improvement to the insulation value of the building shell would immediately lead to a considerable decrease in primary consumption. The uninsulated roof in particular was a major source of heat loss: 44% of the total heat is lost through the roof. But the façades (20%) and windows (28%) were also areas of large losses. The transmission loss (U values) for the various sections of the building shell were far above the maximum standard values for new builds (Table 1).

Using these data, a proposal was drawn up to improve the insulation values of the various building sections by: i) insulating the façades on the inside; ii) insulating the roof and floors; and iii) placing secondary glazing with mobile awnings in the space between the protected and the new windows. Initially a proposal was drawn up (Solution A) in which the exterior walls would be insulated on the inside with a 12 cm thick calcium silicate board with a plasterwork finish. This would provide a U value of 0.26 W/m²K. In this way, the various building sections would meet the current standard values (Table 1) after adaptation. In a second phase (Solution B) an alternative solution for the inside insulation was put forward using 3 cm thick insulating plasterwork, which could provide a U value of 0.62 W/m²K. Insulation on the inside provides a gain in comparison to the original situation, although this does not meet the current requirements according to the energy performance regulations. This would decrease the primary annual energy consumption from 400 kW/m² to 188 kW/m². The new K and E levels would become 27 and 81 respectively: a substantial improvement. However, for the E level, the energy consumption is still too high to be able to call it a nearly energy-neutral office building (i.e. K level lower than or equal to K40 and E level lower than or equal to E40).

POTENTIAL BENEFITS AND RISKS OF IMPROVING THE INSULATION OF MONUMENT FAÇADES

In principle, there are three possible scenarios for improving the façades’ thermal insulation:

Table 1

Overview of the transmission loss for the various sections of the building shell in their initialcondition and the proposals drawn up for improving the insulation. The maximum U values permitted for individual building sections according to the current standards are also included in the table (© KIK-IRPA).

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