If, at the existing hearing, the board of adjustment finds that, by reason of existing construction of buildings or of sidewalks, it would be impractical or undesirable from a planning viewpoint to require the sidewalk to be placed as provided in Sections 12.08.070 through 12.08.120, or in accordance with the master street plan, the board of adjustment may grant a variance from such requirement specifying the manner in which the variance shall be allowed and the condition upon which the permit is to be granted. (Prior code § 2.235)