Sanierungspflicht after buying a house in Germany: the 2026 rules

The notary's appointment is booked, the mortgage is approved, and somewhere in the paperwork a clock starts that most buyers never hear ticking. German energy law gives the new owner of an older house two years to do certain work.

The Sanierungspflicht is the set of retrofit duties in Germany's building energy act, now titled the Gebäudemodernisierungsgesetz (GModG). The one that bites at purchase is section 35: the top floor ceiling or roof must be insulated to a U value of 0.24, and where the previous owner occupied the house on 1 February 2002, the duty passes to the buyer with a two year deadline.

What changed in 2026, and what is the law called now?

The text published by the Federal Ministry of Justice on gesetze-im-internet.de still sits at the address of the old Gebäudeenergiegesetz, but its title is now "Gesetz zur Einsparung von Energie und zur Modernisierung der Wärmeversorgung in Gebäuden", short form Gebäudemodernisierungsgesetz or GModG. The status line records the latest amendment as article 1 of the act of 23 July 2026, published in the Federal Law Gazette as BGBl. 2026 I Nr. 226. Several of the old paragraphs are marked "weggefallen", dropped, among them sections 71 to 73, and the heating rules in part 4 were rewritten around the date of 29 July 2026.

The buyer's duties in part 3, on existing buildings, survived the rename. What follows is what the current text says.

What must a buyer insulate within two years?

Section 35 obliges the owner of a residential building to make sure that top floor ceilings which do not meet the minimum thermal protection of DIN 4108-2 are insulated so that their heat transfer coefficient does not exceed 0.24 watts per square metre and kelvin. The duty counts as met when the roof above is insulated to the same standard or already meets the DIN minimum. Where the insulation goes into a ceiling cavity and the thickness is limited for technical reasons, subsection 2 accepts the greatest thickness the recognised rules of technology allow, at a thermal conductivity of 0.035 watts per metre and kelvin, or 0.045 for blown in or renewable materials.

Subsection 3 is the buyer's clause. In a residential building with no more than two dwellings, one of which the owner lived in on 1 February 2002, the duty only has to be met after a change of ownership following that date, by the new owner, and the deadline is two years from the first transfer of title after 1 February 2002. Subsection 4 lifts the duty for owner occupied buildings of up to two dwellings when the cost of the retrofit cannot be recovered through the savings within a reasonable period.

Section 34 adds the standstill rule: external building components may not be altered in a way that worsens the building's energy quality, unless the altered area is no more than 10 percent of the component group.

What happened to the boiler replacement duty?

The current table of contents lists sections 71, 72 and 73 as dropped, and no section in the present text imposes an operating ban tied to the age of a boiler. A parliamentary question of 16 April 2026, Bundestag Drucksache 21/5405, summarised the government's plan in the same terms: sections 71 to 71p and section 72 of the old act were to be struck, the flat 65 percent renewable requirement abolished and the operating bans for certain heating types withdrawn, with a rising share of carbon neutral fuels for gas and oil heating from 1 January 2029 instead. What the law now regulates is the replacement itself. Section 42 lists ten permitted options when a heating system in an existing building is replaced, from a gas or oil boiler to a heat pump, solar thermal, biomass, hybrid systems, a district heating connection or another innovative solution, and points to sections 43 to 46 for the conditions.

For a buyer who inherits an old gas or oil boiler and replaces it, section 43 matters most. A gas, heating oil or LPG system newly installed in an existing building after 29 July 2026 must deliver a rising share of its heat from biomethane, bio oil, biogenic LPG or hydrogen: at least 10 percent from 1 January 2029, 15 percent from 2030, 30 percent from 2035 and 60 percent from 2040. The share can also be met with a solar thermal system of a set size or a ventilation system with heat recovery, and a hybrid heat pump that covers at least 30 percent of the peak load counts as compliant. Subsection 7 gives a twelve month grace period when a boiler is replaced after an irreparable failure in 2028.

Minimum renewable share of heat for a fossil boiler installed after 29 July 2026

From	Renewable share (%)
1 January 2029		+10%
1 January 2030		+15%
1 January 2035		+30%
1 January 2040		+60%

Section 42a announces the next step: the federal government must present a bill for a green gas and green heating oil quota by 1 December 2026, obliging fuel suppliers to switch heating fuels fully to climate neutral products from 2045. Section 60b keeps a heating check and optimisation duty for water based systems in buildings with at least six dwellings.

What do the energy certificate rules require at a sale?

Section 80 requires an energy certificate, the Energieausweis, to be drawn up when a built plot or a condominium is sold, unless a valid one already exists. For residential buildings with fewer than five dwellings whose building application predates 1 November 1977, the certificate must be a demand based Energiebedarfsausweis, unless the building already met the 1977 thermal insulation ordinance. Subsection 4 sets the timing: the seller or agent must present the certificate at the viewing at the latest, hand it over promptly after the contract is signed, and a buyer of a house with up to two dwellings must attend an informational consultation on the certificate with an authorised person when such a consultation is offered free of charge.

Section 87 governs the advert. Once a certificate exists, a commercial listing must state its type, the final energy demand or consumption figure, the main energy carrier for heating, the year of construction and, for residential buildings, the energy efficiency class.

None of this replaces reading the building itself. A condominium buyer also inherits the declaration of division, which decides who pays for a shared roof, as our guide to the Teilungserklärung explains, and Sweden's version of the certificate is decoded in our guide to the energideklaration.

Ask two questions before the notary: who lived in the house on 1 February 2002, and what does the Energieausweis say about the top floor ceiling. AiMYNDi reads the certificate and the exposé and flags the section 35 clock before you sign.