Cost functions for an exterior wall
Average values for the full costs and energy-related additional costs of exterior wall insulation with a thermal insulation composite system (rigid foam or mineral wool) may be estimated with the following cost function, depending on the insulation thickness. The result applies to one square meter of exterior wall. VAT is included. For an evaluation of the cost effectiveness of an energy modernisation, not the full costs but only the energy-related additional costs are generally taken into account.
Construction costs (full costs) = 2.81 €/cm ∙ X cm insulation + 96,88 €
Included in these costs are average energy-related additional costs. This part of the costs can be determined using the following formula:
Energy-related additional costs = 2.81 €/cm ∙ X cm insulation + 19,77 €
Thus, for an insulation thickness of e. g. 15 cm, the average full costs of the measure (at the price level of 2015) amounted to approx. 139 €/m². In this case, the average energy-related additional costs amounted to about 62 €/m². The actual costs in individual may deviate from the determined values cases due to individual preconditions.
Before carrying out insulation measures, the exterior wall should absolutely be examined with regard to possible moisture damages and to their stability. Costs for such examinations and possibly ensuing repair of faults are counted toward the repair costs. Necessary scaffolding work is disregarded.
The necessary preliminary and additional work as part of repair include, among others:
• the creation of a stable surface,
• the base plaster,
• connection strips, sealing tapes, attachment of decorative elements,
• additional decorative work on window surrounds, coats of paint, and tinting additions,
• dismantling and re-installation of window grilles or banisters, outdoor lights, sockets, and mailboxes, and
• the renovation of rainwater pipes in course of the repair of old facades.
The energy-related modernization costs include, among others:
• insulation including fixation and base rails,
• potential elongation of the roof overhang,
• filling of joints and grinding of insulation material, and
• system-compatible windowsills with respect to enlarged depth of reveals after insulation.