As a homeowner, at some point, you ask yourself the following questions: What does an energetic home renovation actually bring me? How much energy can I save as a result? And what is the greatest potential for savings: in insulation, in replacing windows, in a new heating system …?
In the following, therefore, the potential savings for individual measures are roughly given. The starting point is a “typical” detached house from the 1930s, not insulated, with box windows and a central heating system that is over 20 years old.
Insulation of the facade:
Uninsulated outer walls cause considerable heat loss in winter. The proportion of losses depends, among other things, on the total area of the exterior walls and their energetic state (U-value). The argument that a thick outer wall already exists and therefore no insulation is required in most cases just a misconception. Even old buildings can now be insulated so that they only need a fraction of the previous heating energy.
The U-value of a typical exterior wall for an existing building is, for example, 1.7 W / (m²K). With insulation to the minimum level of 0.24 W / (m²K) required by the Energy Saving Ordinance (EnEV), the heat loss through this outer wall has been reduced by 85 percent.
Insulation of the roof
If the roof is still in its original energetic state and the adjoining rooms are heated, significant heat losses can also be recorded over the roof surfaces. You can see them very well in winter, as the fresh snow melts away particularly quickly on these roofs. In a new roof, a “contemporary” insulation of the roof surface is recommended (and is even prescribed by the EnEV). The additional costs of insulation are low compared to the costs of re-roofing.
By increasing the insulation, it is estimated that up to 70 percent of the heat losses via the roof area can be saved. Overall, this would mean a savings potential – depending on the initial situation – of almost 10 percent for the house.
Insulation of the top floor ceiling
Starting with a pitched roof, as is typically the case, heat losses are also generated in unrenovated buildings to the (often undeveloped) attic. The costs for subsequent insulation are usually very low. By insulating the top floor ceiling, the losses in this area can be reduced by approx. 10 percent. Overall, this would result in a savings potential of around 1 percent (depending on the size of the top floor).
Insulation of the basement ceiling (alternatively insulation of the floor slab)
If the building has an unheated cellar, the building will also lose considerable heat through the cellar ceiling. The insulation of the basement ceiling is also comparatively simple but is often limited by the (low) height of the basement. Optimal insulation can typically save up to 70 percent of losses. Overall, the savings potential is around 5 percent.
Window replacement and, if necessary, insulation or renewal of the roller shutter boxes
The losses over the window areas can be reduced by around 50 percent (and more) by replacing the window. A significant reduction in heat losses is also possible if the “old” (uninsulated) roller shutter boxes are replaced.
Based on box windows, the total savings potential in window replacement to the minimum standard of the EnEV is rather low, sometimes less than 5 percent. The situation is different if there are significant ventilation losses due to the window leaks and the leaks in the roller shutter boxes. However, a general estimate for a “typical” single-family home is hardly possible.
Sum of all measures for the renovation of the building envelope
If all of the above measures for renovating the building envelope are brought up to today’s minimum standard, the heating requirement can be reduced by approx. 75 percent. Suppose you look again at the entire energy balance (heating requirement, water heating requirement, system losses). In that case, the renovation of the building envelope has potential savings of almost 50 percent for this house.
Conclusion: The entire renovation of the building envelope and the heating system
In summary, it can be said that in the present example, the entire insulation of the building envelope (facade, roof, top floor ceiling, basement ceiling, window replacement, if necessary renewal of the roller shutter boxes) results in a savings potential of approx. Almost 50 percent, and through the renewal and optimization, the heating system offers potential savings of up to 35 percent.
The combination of all measures – and renovation to the EnEV minimum standard – results in a savings potential of approx. 75 to 80 percent is possible.