Energy Renovation of a Pre-War Apartment Block
A housing association in Tuzla plans to renovate a 1970s prefabricated panel apartment block: new windows, 12 cm external insulation, and a new gas boiler. The building has single-pipe heating distribution with radiators under windows, no mechanical ventilation, and a history of mould in north-facing bedrooms. The association's consultant proposes a 'deep retrofit' targeting a very low primary energy demand, including airtightness improvements and a mechanical ventilation system with heat recovery, but the budget covers only the envelope and boiler. The tenants include elderly residents on fixed incomes, and rents cannot rise. The panel joints have visible open gaps on the gable facade.
1. Identify the building-physics risks in the proposed renovation and how they interact.
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The measures interact in ways that can make the building worse if sequenced carelessly:
- Airtightening without ventilation: sealing the envelope reduces incidental infiltration that currently dilutes moisture; with no mechanical ventilation, humidity rises and mould risk increases, especially in north-facing bedrooms.
- Thermal bridges at panel joints: insulating the facade while leaving open gable joints can create cold bridges and interstitial condensation at the joints and slab edges.
- Single-pipe heating: adding insulation and new windows reduces heat demand, but the single-pipe distribution cannot be balanced room by room; some rooms will overheat and others stay cold, and the boiler will cycle inefficiently.
- Ventilation and mould: the existing mould is a symptom of insufficient ventilation and cold surfaces; insulation helps surface temperatures but does not solve the ventilation deficit.
A whole-building assessment, including hygrothermal and ventilation checks, is needed before choosing measures.
2. Recommend a phased, budget-constrained strategy and justify the priorities.
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Sequence measures by risk reduction and cost-effectiveness:
- Repair panel joints and airtightness first, with detailing that avoids new thermal bridges; this protects the insulation investment.
- Envelope insulation and windows as a package, with a condensation check at junctions; avoid airtightening beyond what ventilation can handle.
- Ventilation: at minimum demand-controlled or continuous extract in wet rooms and bedrooms; heat-recovery ventilation if budget allows later, with shafts planned now.
- Heating: hydraulic balancing and, where feasible, conversion to a two-pipe system or radiator valves suited to lower temperatures; a new boiler sized to the post-retrofit load, not the old one.
Explain to the association that a low-energy target without ventilation risks mould and tenant complaints, and that the phased plan preserves the option to reach the target later. Protect tenants during works and avoid rent increases by prioritising measures with the best payback.