ONLINE BRUSSELS HERITAGE - ONE-DAY SEMINAR - 11/12/2014

condensation-tight film to the interior surface in order to prevent condensation problems. Such a solution rules out moisture transfer between the wall and the interior (fig. 4b). Drying of the brickwork is thus only possible from interior to exterior, which results in an increase in the average moisture content. However, the insulation materials always remain dry, thus retaining their insulating qualities. Therefore such a solution is of better quality from a technical point of view. The increasing moisture content near the exterior surface does however increase the risk of frost damage and biological attacks. On the other hand, if capillary active insulation materials are used (such as calcium silicate boards or insulating plasterwork] the moisture transfer through the construction, from the interior to exterior, is retained (fig. 4c). On average, this leads to a decrease in moisture content in the brickwork, thus also decreasing the risk of damage to the historical façade elements. This solution is thus the preferable option for maintaining heritage property. However, the fact that the insulation materials can (temporarily) absorb moisture and therefore (temporarily) lose a portion of their insulation value must be taken into account.

Applying interior insulation to historical buildings with brickwork façades is thus not without risk. By insulating the inside walls, heat loss decreases, causing an average increase in the moisture content in the brickwork of the façade and simultaneously making it colder. The combination of these two elements increases the risks of both frost damage and biological attack to the façades. Particuarly when materials are present in the historical façades which create a risk of frost damage, taking a good look at the pros and cons is very important.

RISK-EVALUATION OF FROST DAMAGE WHEN APPLYING INTERIOR INSULATION TO THE FAÇADE OF THE VETERINARY SCHOOL

In order to be able to evaluate the risk of frost damage, the evolution of the temperature and the moisture content in the veterinary school's façades were examined based on the interior insulation choice. This approach was based on the heat and moisture transport in the façade brickwork as a function of the interior and exterior climate and the material characteristics of the cross-section of the façade. Material characteristics such as density D, accessible porosity DO, pore division, capillary water absorption coefficient Acap and degree of capillary saturation wsat were experimentally determined on illuminated samples (table 2). Absent material characteristics, such as thermal conductivity B and moisture permeability u, were estimated in a rational way based on known correlations to the other experimentally determined, material characteristics. A model of the combination of heat, moisture and mass transport was created in the Delphin 5.6 program, developed by the T.U. Dresden.

This study on the influence of the interior insulation on the temperature division and the moisture balance in the façade brickwork concentrated, firstly on the rear façade and secondly on the façade brickwork masonry of the front façade, where the ashlar is made of Euville (table 3). The core of the brickwork, just behind the ashlar, is also made of brickwork masonry on the front façade. The initial situation of each façade was then compared with the condition in which interior insulation based on a 12 cm thick calcium silicate board, and a 3 cm layer of insulated plasterwork, was used.

The results show the evolution of the temperature and moisture content in the cross-section of the wall over time. The evolution of the moisture content is shown in figures 5 and 6, for the rear and front façade respectively, at each

Fig. 4a, 4b and 4c

Overview of the temperature transition (red curve) and the possibility of moisture exchange between the interior and exterior environment (blue arrow) for non-insulated mass brickwork (a) and an interior insulated construction with water and damp proof insulation material (b) and capillary-active insulation material (c) (© KIK-IRPA).

68 | Risk analysis for applying interior insulation in historical buildings: a case study of the former veterinary school in Anderlecht