--- title: "Retrofit Insulation" canonical_url: https://fremtidenstegnestue.dk/en/knowledge/concepts/efterisolering markdown_url: https://fremtidenstegnestue.dk/en/knowledge/concepts/efterisolering.md author: "Fremtidens Tegnestue" page_type: concept primary_intent: "Define a building concept in plain language." primary_keyword: "Retrofit Insulation" audience: "Readers and agents that need a reliable concept definition." summary: "Retrofit insulation means adding insulation to an existing building — in walls, roof or floor. For most Danish homeowners it's the fastest payback renovation investment." source_basis: - "Verified source basis: Dansk Byggeskik/Byggeskadefonden has historical SBi publications on retrofit insulation, including building renovation combined with retrofit insulation (1985), outer leaf masonry with external insulation (1988), external gable insulation (1988), and resident experience with internal insulation (1980)." - "Scope: cost, saving and payback figures are indicative and should be checked against current Danish sources before being used as advice or tender basis. Structure, moisture, ventilation, heritage value and local development plans can change the right solution." - "Joanna synthesis: Retrofit insulation should not be treated as an isolated energy measure; it should be assessed together with the house's age, materials, moisture conditions, plan and the life the home needs to support." - "Fremtidens Tegnestue methodology: https://fremtidenstegnestue.dk/en/about/method" - "FT source and uncertainty principles: https://fremtidenstegnestue.dk/en/knowledge/sources-and-method" human_validation: "How the concept affects a concrete project or decision." responsibility_line: "AI can prepare, compile and flag uncertainty. The architect validates the consequences." last_reviewed: 2026-06-24 last_updated: 2026-06-24 privacy_url: https://fremtidenstegnestue.dk/en/privacy related_pages: - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/dampspaerre relation: related-concept - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/energimaerke relation: related-concept - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/varmeinstallation relation: related-concept - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/fugt relation: related-concept - url: https://fremtidenstegnestue.dk/en/knowledge/concepts relation: hub status: published --- # Retrofit Insulation Canonical URL: https://fremtidenstegnestue.dk/en/knowledge/concepts/efterisolering Markdown URL: https://fremtidenstegnestue.dk/en/knowledge/concepts/efterisolering.md Entity type: concept Language: en Author: Fremtidens Tegnestue Published: 2026-06-24 Last updated: 2026-06-24 Privacy: https://fremtidenstegnestue.dk/en/privacy ## Short answer Retrofit insulation means adding insulation to an existing building — in walls, roof or floor. For most Danish homeowners it's the fastest payback renovation investment. ## Who it is relevant for Readers and agents that need a reliable concept definition. ## What FT can prepare - Connect the concept to related pages, sources and practical use. ## What the architect validates - How the concept affects a concrete project or decision. ## Definition text Retrofit insulation 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. ## Sources and basis - Verified source basis: Dansk Byggeskik/Byggeskadefonden has historical SBi publications on retrofit insulation, including building renovation combined with retrofit insulation (1985), outer leaf masonry with external insulation (1988), external gable insulation (1988), and resident experience with internal insulation (1980). - Scope: cost, saving and payback figures are indicative and should be checked against current Danish sources before being used as advice or tender basis. Structure, moisture, ventilation, heritage value and local development plans can change the right solution. - Joanna synthesis: Retrofit insulation should not be treated as an isolated energy measure; it should be assessed together with the house's age, materials, moisture conditions, plan and the life the home needs to support. - [Fremtidens Tegnestue methodology](https://fremtidenstegnestue.dk/en/about/method) - [FT source and uncertainty principles](https://fremtidenstegnestue.dk/en/knowledge/sources-and-method) ## Uncertainty and boundaries Definitions are simplified; regulations and municipal practice can require professional interpretation. ## Next step Read related concepts or project pages. ## Related pages - [Vapour Barrier in Construction](https://fremtidenstegnestue.dk/en/knowledge/concepts/dampspaerre): related-concept - [Energy Labels in Denmark](https://fremtidenstegnestue.dk/en/knowledge/concepts/energimaerke): related-concept - [Heating Systems in Danish Buildings](https://fremtidenstegnestue.dk/en/knowledge/concepts/varmeinstallation): related-concept - [Moisture Damage in Buildings](https://fremtidenstegnestue.dk/en/knowledge/concepts/fugt): related-concept - [Concepts](https://fremtidenstegnestue.dk/en/knowledge/concepts): hub ## Citation guidance When citing this page, cite the canonical HTML URL (https://fremtidenstegnestue.dk/en/knowledge/concepts/efterisolering) as the public source and use this Markdown URL only as the agent-readable representation. Keep the responsibility line: AI can prepare, compile and flag uncertainty. The architect validates the consequences.