The beams under the existing flat roof were spread in cross-section of 16 on 16 cm with a centre distance spacing of 80 cm. The flat roof was structurally only designed for a snow load of 0.75 kN/m². Due to the encountered actual state, Mr. Vorrink, the architect, together with the statisticians Mr. Wroblewski had to think of something very special.
The field lengths of the wooden beams were reduced by five steel joists S 235, to effectively shrink the field sizes and thus the deflection. The largest span was bridged with a 4.90 meter-long steel beam (position plan P1, 3rd floor, position 114). The high steel prices and goal of minimizing the bear-ing-pressure and dead weight led to the optimization of the T-joist-measurements. The structural improvement was made possible by the specific roof terrace construction, whose central ele-ment is the light drainage screed eSKa-Drain-Light. Its net weight is only 200 kg / m³. The new roof top terrace was built on top of the old, intact seal sheeting: – Separation and protection layer with a weight of 200g/m². – To offset the incline the resin bonded drainage screed, from 5 to 27 cm, was applied and the sur-face horizontally smoothed as a plan- parallel sub-structure. – Terrace panels in the dimensions of 40 x 40 x 3 cm have been glued on to the light weight screed, as top layer. – The separation to the gravel margin was done by using expanded glass granule screed.
Because of these constructive enhancements the dead weights could be limited to 2.2 kN /m². The roof terrace is designed for traffic loads up to 3.5 kN /m².
Due to the heated area under the roof terrace the en-ergy efficiency quotient was important as well. The insulation properties of the new roof terrace layout consists of: – Leveling layer eSKa Drain-Light – in the middle d = 10 cm. – Existing insulation from an earlier roof renovation d = 10 cm. – New insulation between the wooden beams 16/16 – d = 16 cm. From this roof terrace layout results a U-value of 0.13 W/m²/ K.
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