De ontwikkeling van (kosten)optimale gevelrenovatiestrategieën voor residentiële hoogbouw



Klaas Calle

Supervisors: prof. J. Moens, dr. ir. arch N. Van Den Bossche, ir. arch. S. Mangé

Abstract- For residential highrise the facade is the most important part of the building envelope.  Therefore, and because of the high need for renovation of this type of buildings in Belgium, this study develops a model to quickly evaluate facade renovation strategies for a specific building. The model makes thermal and financial calculations for all proposed strategies. The financial calculations are also made for the long term. This means that even fuel costs, maintenance and residual value are taken into account. As well as specific results for a case study, general trends are described and declared.

Keywords-facade renovation, highrise, cost effectiveness, renovation strategies


For small scale residential buildings there are some models to evaluate cost effectiveness of renovation strategies [1, 2] but these are not useful for residential highrise, since for highrise the facade is much more important than it is for normal housing. On the other hand, the existing models use reference buildings to make conclusions for a whole type of building without taking the existing construction into account. Which is of course very important when you want to  renovate. Therefore, a calculation tool which can evaluate facade renovation strategies on thermal and financial base and which takes the existing construction into account is developed. For all costs from demolition to renovation, maintenance and energy assumptions are made and the calculation is run through.


First, previous studies are examined by a small scale literature study. Also, some research is done on how residential highrise, ready to renovate anno 2015, is built [3]. Further on, a specific case study building called Kielpark is technically examined. All standards for facade renovation of highrise are listed and discussed for the case Kielpark. With this in mind, different plausible types of facade renovations are selected. After this, it is explained how the calculation model makes the thermal [4] and the financial [1] calculation on long-term. For the financial section, the total actual cost is calculated. The total actual cost is defined by renovation, fuel maintenance cost and residual value. The long term costs (fuel and maintenance) are of course converted to  the present value. The power of the model is that for one strategy different types of compositions can be evaluated, such as different thicknesses in insulation package, different manipulations on the existing building and so on. All other thermal and financial assumptions can also be modified in a user-friendly Office Excel input. The different proposals for different pieces of the facade are combined into unique combinations. As well as for the facade sections as for the windows different proposals are made. All these hundreds of thousands of combinations are run through the calculation model and plotted onto a graph. The graph is drawn for the total actual costs in function of the U-value of the building envelope after renovation. 


For the different strategies given in this table the calculations are made for the case Kielpark. 

Option 1

Interior insulation – Aerated concrete

Option 2

Interior insulation – Interior insulation wall

Option 3.1

Exterior insulation – New concrete panels (with open joint system)

Option 3.2

Exterior insulation – New concrete panels (with closed joint system)

Option 4

Exterior insulation – Plaster

Option 5.1

Exterior insulation – Glass fiber reinforced concrete panels (small)

Option 5.2

Exterior insulation – Glass fiber reinforced concrete panels (large)

Option 6

Exterior insulation – Precast concrete sandwich panel

Option 7

Exterior insulation – Precast wood sandwich panel

Afbeelding verwijderd.

The calculation combines and plots all proposals  onto the graph. For the given options in the table, nine thicknesses are proposed for each of the five facade sections of the Kielpark. Also, seven types of windows are proposed. This means that for each option (color) 9^5*7= 413343 points are drawn. Because of the mass of points, together they become big stains instead of individual points. Option 1 (blue) is the most cost effective because there is a very low total actual cost over a period of 30 years. However, it is not possible to reach very low Umean values for the whole building facade. The shape of the spots drawn gives insight into how to renovate cost effectively. For each option (color) one can discover seven clusters of points, because there are seven different types of windows proposed. For a more exact insight in how the spots are formed the next graph is a zoom of one of the spots of option 1. 

Afbeelding verwijderd.

The colors from black to brown (thin to thick) show which points are defined by which insulation thickness for facade section 1. Section 1 is chosen because this is the biggest section of the facade and therefore the results give the most clear insight. For option 1, one can see that thick insulation packages have low U-values but high total actual costs. For other options the cluster has a completely different shape.

Afbeelding verwijderd.

For option 4 it is more cost effective to insulate with 120 mm than with 200 or 50 mm, because for 50 mm the fuel cost over 30 years is too high while for 200 mm the renovation cost is too high.


When facades get renovated it is important to achieve a U-value that is as uniform as possible for the whole facade. To achieve that uniformity, the building envelope sections witch already have a decent U-value before the renovation should get a less thick insulation. The windows make a big difference in the U-value but they also cost a lot of money, which is why changing them is never cost effective for this case and for the present economic situation. The long term cost calculations have also shown that thick insulation protects owners better against a changing economy.


[1] Van der Veken, J., Creylman, J., & Lenaerts, T. (2013). Studie naar kostenoptimale niveaus van de minimumeisen inzake energieprestaties van gerenoveerde bestaande residentiële gebouwen.

[2] Verbeeck, G. (2007). Opimalisation of extremely low energy residential buildings.

[3] Hoet, A. (2013). Renovaties van sociale hoogbouw in België.

[4] Belgisch staatsblad. (2010). Transmissie referentie document.



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Universiteit of Hogeschool
Universiteit Gent
Thesis jaar
Prof. Jan Moens