Flow velocity in ventilated flat roofs

Efficient influence analysis with generic 2D models


The air exchange rate plays an important role in the construction of rear-ventilated flat roofs. A sufficient air flow must be ensured in the roof gap so that the wood of the supporting roof structure can dry sufficiently. When dimensioning the roof geometry, the interaction of roof length, roof pitch and gap height must therefore be taken into account. It is equally important to take into account the influence of the roof structure and roof extensions such as the gutter, the mansard bend and the perforated metal sheets installed.


To identify the influences of these various factors, a generic 2D CFD was developed for RHEINZINK GmbH & Co. KG, a generic 2D CFD calculation model was created. This two-dimensional model allows the calculation of a large number of variants in a very short time while simultaneously taking into account all the influencing factors mentioned.


The calculation model allows both the calculation of the air speed in the roof gap at a given external wind speed as well as in calm conditions, when only the heating of the air in the roof gap is the cause of the air movement.


The results of the simulations provide RHEINZINK GmbH & Co. KG a better insight into the flow conditions in the roof gap and allow customers to select the height of the air gap according to their needs.

You might also be interested in the following pages:

Steady-state flow analysis

Thermal flow analysis