Opinion by

The Borough of Newville brought this action to recover of the defendant the cost of laying a sidewalk in front of her property, alleging that she had failed to construct the same after having duly received notice to do so. The question most earnestly contested at the trial in the court below was whether the defendant had received a written notice to lay the sidewalk. The court submitted that specific question to the jury which found that Jacob Koch, the high constable of the borough, had served a written notice upon the appellant to lay the sidewalk. The appellant here contends that there was no evidence to warrant this finding. There was clearly sufficient evidence to warrant the finding that the borough council had adopted a resolution directing the secretary to write out the notices and have the high constable deliver the same to the parties to whom they were addressed. The only evidence that Koch, the high constable, had served any notice upon this appellant consisted of an affidavit of that officer to his return of the notice, stating that he had served the same upon this appellant by handing a true and attested copy thereof to her personally. This statement was sworn to and subscribed before Brandt, the chief burgess of the borough. The appellant objected to this evidence upon the ground that it did not appear that either Koch, as high constable, or Brandt, as burgess, before entering upon the duties of their offices, had filed the affidavits and bonds required by law. Brandt and Koch were duly elected to their respective offices and it is not denied that they were regu*128larly acting as such, they were officers de facto^ and this being the case, the appellant could not in this collateral proceeding, raise any question as to the existence of their functions, as distinguished from the manner in which those functions were exercised: Keyser v. McKissan, 2 Rawle 138; Clark v. Commonwealth, 29 Pa. 138; Campbell v. Commonwealth, 96 Pa. 344; Coyle v. Commonwealth, 104 Pa. 117. The officers having been duly elected and acting under color of title to their respective officers, this appellant could not in this proceeding raise any question as to their right to so act. The borough council having ordained that the notices should be served by the high constable it became the duty of that officer to serve the notices, “and attest the service of the same by affidavit in writing signed by him” under the provisions of the 13th section of the Act of April 3, 1851, P. L. 324. The affidavit of service was the official act of the high constable, required by law in the performance of his duty, and, it being admitted that the officer was dead, the affidavit was properly received in evidence and was sufficient to warrant the jury in finding the facts to be as stated: Ross v. Rhoads, 15 Pa. 163; Russel v. Werntz, 24 Pa. 338. This disposes of the first, second, third and fifth questions involved, as stated by the appellant.

The remaining question attempted to be raised is whether a borough has authority to require the laying of a sidewalk upon a street when it has never by ordinance established a grade for the street. The answer to this question must, in any particular case, depend upon the circumstances of that case. A borough is without authority to require a property owner to construct a sidewalk at a grade substantially different from that of the existing grade of the street, when it would require the property owner to do any considerable amount of grading: Chester City v. Lane, 24 Pa. Superior Ct. 362. An ordinance of council is the proper legal expression of the municipal authority in reference to all matters of *129changing the grade of a street, or of the sidewalks thereof : McKnight v. City of Pittsburgh, 91 Pa. 273; Chester v. Eyre, 181 Pa. 643. When, however, a street has already been opened and used as a public highway, it is competent for the municipal authorities to require sidewálks to be laid at the existing grade, although the council has not adopted any paper grade for the street: Carlisle Borough v. Long, 47 Pa. Superior Ct. 628; Canton Borough v. Williams, 67 Pa. Superior Ct. 239. The evidence in this case disclosed that the street in question was a State highway, the sidewalk was constructed, at the grade of the highway, and the appellant is not asked to pay for any grading.

The judgment is affirmed.