Energy
What should I insulate first?
Short answer
Often the roof. For a Dutch semi-detached house, roof insulation saves about 340 m³ of gas per year.
Explanation
Warm air rises; an uninsulated roof loses a lot of heat. Roof insulation is relatively simple and pays off well. Milieu Centraal compares the return to about 5 % interest. Strict maximum U-values apply to new builds in Flanders.
Rules of thumb
- Pitched roof to Rd 3.8 (NL): terraced house about 320 m³, semi-detached about 340 m³, detached about 550 m³ of gas per year. [SW-S47]
- Flanders new builds 2024: U-value of roof, wall and floor at most 0.24 W/m²K. [SW-S50]
- Lower U-value = better insulation; higher R-value = better insulation. [SW-S50]
Pitfalls
- After insulating, natural air leakage falls; take extra care with ventilation. [SW-S30]
Search terms
These search terms are in Dutch; only terms that also find a topic in English are links.
isolatie dakisolatie U-waarde Rd-waarde
Read also
- Is my home ready for a heat pump?
- How much ventilation does a room need?
- Must I renovate my home by law (Belgium)?
General information, not personal advice. Check the source and reference date.
Sources
- SW-S30 Tips voor beter en energiezuiniger ventileren — Milieu Centraal (Reference date 2026-09-27)
- SW-S47 Dakisolatie: lagere energiekosten — Milieu Centraal (Reference date 2026-09-27)
- SW-S50 Nieuwe EPB-eisen voor 2024 voor nieuwbouw en renovatie — VEKA (Vlaams Energie- en Klimaatagentschap) (Reference date 2026-09-27)
Reference date: 2026-09-27 · Translated with AI from the Dutch original.