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Insulation: Exterior Wall, Roof, or Basement — Where to Start?

Not all insulation delivers equal returns. How to set priorities, avoid common mistakes, and make the most of subsidies.

As of: May 2026·6 min read

⚡ In brief: Start with the top floor ceiling or basement ceiling — low cost, quick payback. Facade insulation has the biggest impact but is most cost-effective when combined with planned facade work. Up to 20% subsidies (with iSFP bonus).

Why the Order Matters

Renovation should be planned from outside in: First improve the building envelope, then adjust the heating. If you replace the heating first and insulate later, you end up with an oversized system — and overpaid.

But not every insulation measure is equally cost-effective. The right order depends on your building, budget, and planned maintenance work.

Insulation Priorities

1

Basement Ceiling & Top Floor Ceiling

The cheapest measures with the quickest payback. Insulating the top floor ceiling is even a GEG obligation for unheated attics. Basement ceiling insulation from below can often be done without a contractor.

💰 €30–60/m²⏱️ Payback: 3–5 years📉 Savings: 5–10%
2

Roof / Sloped Roof

Especially important when the attic is used as living space. Between-rafter insulation is cheaper than above-rafter insulation but slightly less effective. Best combined with roof re-covering that's due anyway.

💰 €100–250/m²⏱️ Payback: 8–12 years📉 Savings: 10–20%
3

Exterior Wall / Facade (ETICS)

The largest surface area and therefore the greatest savings potential — but also the most expensive measure. Especially worthwhile when facade painting or plastering is due anyway. The additional cost for insulation then represents only a fraction of total costs.

💰 €100–200/m²⏱️ Payback: 10–15 years📉 Savings: 15–25%

Avoid Common Mistakes

⚠
Insulating too thin: Labor costs (scaffolding, plaster) apply regardless. Don't save on insulation thickness — the extra cost is small, the impact much better.
⚠
Ignoring thermal bridges: Window connections, balconies, and roller shutter boxes are typical weak spots. Without proper detail solutions, mold can develop.
⚠
Wrong vapor barrier placement: For interior insulation or roof insulation, the vapor barrier must be on the warm side. Mistakes lead to moisture damage.
⚠
Not adjusting heating: After insulation, heat demand drops. Without hydraulic balancing and heating curve adjustment, you waste potential savings.

Subsidies for Insulation

Insulation measures are subsidized as BEG individual measures via BAFA:

  • ✓ 15% base subsidy
  • ✓ +5% iSFP bonus = 20% total subsidy
  • ✓ Max. eligible costs: €30,000 per unit (€60,000 with iSFP)
  • ✓ Apply BEFORE starting the work!

💡 The Anyway Principle

The most cost-effective insulation comes from combining it with planned maintenance: Facade painting? Add insulation at the same time. Re-roofing? Add above-rafter insulation. This way, you only pay the additional cost for insulation — not the entire construction measure.

Which Insulation Pays Off for You?

With an individual renovation roadmap (iSFP), we determine which measures have the greatest impact for your building.

Get Free Consultation →Calculate Savings →