
By tradition, when the roof is finished, a little spruce decorated with ribbons is put up to mark this occasion. The roofing work is the most dangerous and trying part of the construction, so the completion of this is a significant achievement.

Majcoat[1] by Siga is a "driving rain-proof and diffusion-open breathable membrane" that creates a windtight envelope.

Wigluv[2] also by Siga is used to seal the overlap areas between the sheets.

[1] Link to the page about Majcoat.
[2] Link to the page about Wigluv.