Cost functions for a pitched roof
Average values of the full costs for retrofit insulation from the outside (polyurethane or mineral wool) in course of a renovation of the roofing can be estimated with the following cost function, depending on the insulation thickness. The result pertains to one square meter of roof area. 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) = 2.77 €/cm ∙ X cm insulation + 151.01 €
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 = 2.77 €/cm ∙ X cm insulation + 11.31 €
Thus, for an insulation thickness e. g. of 20 cm, the average full costs of the measure (at the price level of 2015) amounted to approx. 206 €/m². In this case, the average energy-related additional costs amounted to about 67 €/m². The real costs in individual cases may deviate from the determined values due to individual preconditions.
The necessary work as part of a renovation of the roofing includes, among others:
• covering of the roof,
• disposal of the building components,
• replacement of the roofing, incl. all connections and plumbing work, and
• costs for roof hatches or chimney renovations.
The energy-related modernization costs include, among others, the costs for:
• a potential enlargement of the rafters’ vertical dimension (to increase the possible thickness of insulation), and
• additional fascia and barge boards.
he costs for scaffolding work as well as measures regarding dormers and roof windows are not included. Potential extensions of roof overhangs as part of an insulation measure of the exterior walls were not taken into account within the costs for roof insulation.
Before carrying out insulation measures, the roof construction should be examined with regard to possible moisture damage and its stability. Costs for such examinations and possibly ensuing repair of faults are counted toward the repair costs.