Key legal question
Whether the costs of replacing a roof window with a roof dormer are deductible maintenance expenses or non-deductible value-enhancing renovation costs.
Extracted holding
The expenditure was a conversion/extension producing value increase; only the repair-related portion of CHF 1,000 was deductible.
Extracted reasoning
The work did not merely repair or renovate the existing window but replaced it with a roof dormer. Mixed expenditure is deductible only to the extent of the maintenance element, which must be estimated. The taxpayers did not prove higher repair-related costs.