Renovating a Half-Timbered House in Siegerland — A Case Study
From assessment to results: How a typical Siegerland half-timbered house was energy-renovated.
The Starting Point
A typical Siegerland half-timbered house: built around 1920, partially rendered facade with visible timber framing on the gable end, rubble stone base, gable roof with slate covering. Living area approx. 140 m², inhabited by a family of four.
Condition Before Renovation
- Energy certificateConsumption index 285 kWh/(m²·a)
- HeatingOil low-temperature boiler, built 1998, 25 kW
- Heating oil consumptionapprox. 3,500 liters/year (≈ €4,200)
- WindowsSingle glazing ground floor, double glazing (1992) upper floor
- RoofUninsulated, exposed rafters in attic
- FacadeTimber frame without insulation, infill panels with clay (approx. 15 cm)
- BasementUninsulated, rubble stone walls, damp at base level
The Special Challenges
Preserve Visible Timber Frame
The gable end with visible timber framing is under ensemble protection. External insulation is not possible here — interior insulation is the only option.
Moisture at Base Level
The rubble stone base had no horizontal barrier. Rising damp had to be eliminated before insulation.
Irregular Wall Thicknesses
Timber frame walls are not flat. Interior insulation had to be adapted to every irregularity — standard boards aren't sufficient.
Ventilation Concept in Old Building
After window replacement and sealing, controlled ventilation is required — but routing ducts through timber framing is challenging.
The Measures Implemented
- 1
Roof insulation (between + under rafter)
14.500 €22 cm wood fiber insulation between rafters + 6 cm under-rafter insulation. New vapor retarder (humidity-variable). Slate covering preserved.
- 2
Interior insulation timber-frame gable
12.800 €6 cm calcium silicate boards, fully bonded with lime plaster. Hygrothermal simulation performed beforehand. No vapor barrier needed (capillary-active).
- 3
External insulation street side (ETICS)
18.200 €14 cm wood fiber ETICS on the rendered street side (no visible timber). Silicate render as finish coat.
- 4
Window replacement
16.400 €12 new wooden windows with triple glazing (Uw 0.9). Ground floor heritage windows with glazing bars. Window reveals insulated inside.
- 5
Basement ceiling insulation
5.800 €10 cm mineral fiber applied from below. Horizontal barrier retrofitted at base level (injection method).
- 6
Heating replacement: air-water heat pump
26.500 €11 kW monoblock heat pump (propane R290), installed at house side. Buffer tank 500L, hot water tank 300L. Existing radiators kept (generously sized).
- 7
Decentralized ventilation with heat recovery
5.200 €6 decentralized ventilation units (operated in pairs) with 87% heat recovery. Core holes on rear side.
Costs and Subsidies
- Total measure costs99.400 €
- BEG grant building envelope (20%)−13.540 €
- BEG grant heating (35%)−9.275 €
- BEG grant ventilation (20%)−1.040 €
- Total subsidies−23.855 €
- Own contribution75.545 €
- KfW supplementary loan (low-interest)75.545 €
The Result
285
kWh/(m²·a)62
kWh/(m²·a)- Energy savings78 %
- New heating costs/year~950 €
- Savings/year~3.250 €
- CO₂ reduction~8,5 t → ~1,2 t
💡 The family saves around €3,250 in heating costs annually. With an own contribution of €75,545 and the low-interest KfW loan, the renovation pays for itself in about 18 years — significantly faster with rising energy prices.
What We Learned
Timber Framing Needs Experience
Not every tradesperson can work with timber framing. Choosing the right specialist companies was crucial — especially for interior insulation.
Hygrothermal Simulation Prevents Errors
The building physics calculation before interior insulation showed that 6 cm calcium silicate is the optimal thickness. Without simulation, it would have been easy to over- or under-insulate.
Heat Pump Works Here Too
Despite old building with radiators: after building envelope renovation, the flow temperature dropped to 45°C — ideal for the heat pump. COP in the first winter: 3.6.
The iSFP Paid Off
The individual renovation roadmap determined the right sequence and secured 5% extra funding on every building envelope measure.
Renovate Your Half-Timbered House?
Every half-timbered house is different. We create an individual renovation roadmap that optimally combines building physics, heritage protection, and funding options.
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