The University of Helsinki has been facing the problem of water leaks in roofs during recent winters. Leaks have been detected especially in mechanically seamed sheet metal roofs and also in repaired and renewed roofings. University building repairs are often limited by their building conservation decisions. Therefore repairs must be designed in a way that does not change the facade significantly, and each change will need to be well-founded. A team of multiple experts has been created to ponder leakage causes and ways to fix them.

Flaws in roofings water resistance, the climates of the previous winters and increased heat loads and poor ventilation in the attics are believed to be the causes of water leakages. Temperature in the attic is high due to large heat loads, a thick blanket of snow on the roof acting as a good thermal insulation and ventilation that is not sufficient to keep the attic cool. Warm roof melts snow and the melt-water streams to the colder eaves and freezes again. Formed ice stems melt-waters and as strip steel roofing doesn’t resist water pressure, water leaks through seams.

The expert team has gathered a list of instructions for design of a trouble-free roof. The purpose of the thesis is to select the main points of the list by interviewing the team members and perform workable structure models considering also conservation aspects. The theory of the thesis is based on the general Finnish strip steel roof design guidelines and laws concerning building conservation.

Installing the roof underlay, improving thermal insulation and air-tightness of air conditioning room, ventilation ducts and roof slab and enhancing ventilation in the attic turned out to be the primary operations of roof renovations. Executing these operations simultaneously will make roof waterproof and cool which reduces the forming of ice at eaves.