Facts
The complainant is the owner of plot GB Solothurn No. 515, which adjoins the inner courtyard of Hotel [D.] to the south. The hotel property (GB Solothurn No. 514) was initially used by Real Fund [D.] as the building right holder and later by [C.] (respondent 2).
In 2014, the Solothurn municipal building commission granted a permit for the conversion of the hotel, the addition of a courtyard-side lift and staircase, and the redesign and change of use of the inner courtyard; in 2015, a permit followed for the attic extension. After objections by the complainant, he concluded a settlement with Real Fund [D.] on 4 May 2015, under which the change of use of the inner courtyard to a car park was waived and the courtyard was to be used as a green area, possibly a children's playground.
On 12 August 2016, [C.] applied for a permit to redesign the inner courtyard. The building authority granted this on 4 April 2017 without a noise expert report. It did not consider the noise complaints concerning the terrace, as its use was deemed authorised. The Solothurn Cantonal Administrative Court did not entertain the appeal concerning the design and type of use of the inner courtyard and otherwise dismissed the appeal (judgment of 8 August 2019, VWBES.2017.163).
By appeal in public law matters of 16 September 2019, the complainant requested the annulment of the lower court's decision and an order directing the building authority to obtain, before any new building permit, a noise expert report for the entire inner courtyard including garden and terrace, as well as the approval of the cantonal environmental office. The Administrative Court and the respondents requested dismissal. The Federal Office for the Environment BAFU considered the contested decision non-compliant with environmental protection legislation.
The essential issue was whether the building authority should have obtained a noise expert report under Art. 36 NAO before granting the permit. The Administrative Court answered in the negative, arguing that the inner courtyard was not a facility within the meaning of the EPA, that the terrace was authorised, that the number of guests in the inner courtyard was limited (approx. 30 persons, summer half-year, 8 a.m. to 10 p.m.), and that noise from conversations was not capable of reaching the planning values for sensitivity level III. The complainant argued that the terrace was not authorised, had undergone significant changes, that noise propagation had changed due to structural alterations, that a private noise expert report showed exceedances of limit values, and that up to 90 or 150 persons could be accommodated in the inner courtyard. The BAFU stated that the change of use of the terrace required a permit and had not been authorised, and that the facade configuration intensified sound reflections.
Considerations
The appeal in public law matters against the final cantonal decision is admissible under Art. 82 let. a, 86 para. 1 let. d and 90 FSCA. As a neighbouring property owner, the complainant is entitled to appeal under Art. 89 para. 1 FSCA. The appeal is therefore admissible.
The Federal Supreme Court is bound by the facts established by the lower court (Art. 105 para. 1 FSCA). A correction or supplementation is only possible in cases of obvious inaccuracy or violation of law within the meaning of Art. 95 FSCA (Art. 105 para. 2 FSCA). A complaint regarding the facts (Art. 97 para. 1 FSCA) must be substantiated.
Under Art. 36 para. 1 NAO, the enforcement authority investigates external noise immissions from stationary installations where there is reason to assume that the limit values are or will be exceeded. A preliminary assessment is sufficient for this; it is enough that an exceedance appears possible and cannot be excluded. The authority is then obliged to investigate, without discretion. High requirements regarding the probability of an exceedance may not be imposed.
The lower court assumed that the terrace was authorised and that a building permit precluded further noise investigations. The Federal Supreme Court disagrees: the exposure limit values must be complied with throughout the entire operating life of an installation. A building permit does not confer acquired rights with respect to a noise situation that contradicts applicable law; it is issued subject to later emission restrictions. Art. 36 NAO applies at all times, including after a permit has been granted. However, a recently granted permit may increase the requirements regarding the probability of an exceedance of limit values where the noise immissions were assessed as compliant and additional immissions are only minor; the circumstances of the individual case must be taken into account.
Whether the terrace has already been authorised need not be decided, as this is not decisive for the question of noise investigation. What matters is the total noise from the terrace and inner courtyard. The enhancement of the terrace through improved access is undisputed, as is…