Retrofit insulation (efterisolering) means adding insulation to a building that’s already standing — as opposed to new construction where insulation is incorporated from the start. For most Danish homeowners, it’s the renovation investment with the fastest payback.
Why does it matter to you?
Most Danish homes built before 1980 are significantly under-insulated by modern standards. Retrofit insulation can:
- Reduce heating consumption by 20–40%
- Improve indoor comfort (more even temperatures, warmer floors and walls)
- Raise the energy rating and property value
- Reduce your carbon footprint
The Danish Energy Agency estimates that retrofit insulation is the most cost-effective climate measure available to private homeowners.
The main retrofit options
Loft insulation: The easiest and cheapest solution. Insulation is laid on top of existing insulation in the unoccupied attic. Typically costs DKK 30,000–80,000 and pays back in 5–10 years.
Cavity wall insulation: Granules or foam are pumped into the cavity that typically exists in brick walls built from the 1930s to 1980s. Costs DKK 20,000–50,000.
External wall insulation: New insulation and facade system installed on the outside of the existing wall. More expensive (DKK 100,000–300,000) but most effective — eliminates thermal bridges.
Internal wall insulation: Insulation added on the interior side. Cheaper but reduces room size and requires careful vapour barrier installation.
Floor insulation: Added below the floor in a crawl space or as part of floor replacement.
Important considerations
Retrofit insulation changes the moisture balance within the structure. Always ensure a correct vapour barrier and ventilation — otherwise you risk mould.
Frequently asked questions
Can I get a grant for retrofit insulation in Denmark?
Yes. The Danish Energy Agency offers grants through the Bygningspuljen and other schemes. Check sparenergi.dk for current subsidy opportunities.
When is retrofit insulation not a good idea?
If the structure is already moisture-damaged, the damage must be repaired first. And in listed or heritage-assessed buildings, external insulation may not be permitted.
What is the U-value?
The U-value (thermal transmittance) indicates how much heat is lost through a building element. The lower the U-value, the better the insulation. BR18 requires values of 0.15–0.30 W/m²K depending on the construction type.