Insulation companies and homeowners must make a thorough investigation of cavity walls to see if bats have made their home there, the country’s highest administrative court has ruled.

The case centred on an insulation company in Best which, the provincial authorities claimed, did not do enough to check for bats before installing cavity wall insulation.

Bats are a protected species but very little is being done to keep them safe from the ‘rampant insulation cowboy practices of the last 10 to 15 years’, bat research foundation SEVON said.

The company in question breached the due care clause in nature protection law, because it only looked inside the walls with a camera, the Council of State said in its ruling.

That, the court said, is not enough because some bat species are tiny and easily overlooked. Old insulation material, pipes and rubble may also hide them from view.

Insulation companies must now first do a quick scan to determine if there are openings in the wall where bats can come in. If that is the case, the wall must be repeatedly investigated for bats by an ecologist.

The decision may have far-reaching consequences for the current home insulation drive. Investigations can take months and there are not enough ecologists around to monitor every project.

IsoSun had been told to carry out a full investigation by the provincial authorities in 2019 but took the case to the High Court instead.

In total, 46 experts and organisations, including insulation companies, and environmentalists, took part in a public consultation exercise about the problem organised by the Council of State earlier this year.