Everyone who rents out a property in Norway is required to measure the radon concentration in the indoor air of the rental property.
The requirement applies to all rental properties, both public and private. The rental of a room connected to one's own home is also included. Apartments located from the third floor above ground level are usually exempt from measurement.
The landlord must be able to provide documentation that the radon levels in the property are safe. This documentation must be available to both the tenant and during any inspection.
Please read more at Ås municipality's homepage about Radon in rental properties (in Norwegian)