Population growth in a number of central European cities necessitates the creation of additional living spaces within the existing urban settings. Toward this end, densification via rooftop extension of existing buildings can provide a partial solution. As the requirements regarding energy performance, summer-time thermal comfort, and structural integrity of attic expansions have been increasingly tightened, planners must carefully assess the advantages and disadvantages of different construction possibilities. Focusing specifically on timber construction as a kind of reference, the present contribution includes a comparison of six different (both conventional and novel) construction solutions for roof top extensions in view of different performance criteria, such as ecological footprint, impact on energy indicators, summer overheating mitigation, cost, and construction time. To conduct the comparison in a transparent manner, the selected construction methods were virtually applied to a case-study building and assessed via multiple tools, including a numeric thermal simulation application.