Roof drain with discharge control, FDE

Roof drains with flow regulation, type FDE, are used for throttling the discharge from flat roofs functioning as retention facilities.

Type FDE is made for a specific capacity and typically within 0.1 l/s to 4.5 l/s.

Mosbaek’s roof drain has a design giving an extremely good braking effect ensuring smaller discharge than obtained with simple control technics with same orifice opening. This makes it possible to control very small amounts of water. See the regulator’s characteristic illustrated on the curve.


The roof drain with regulation provides hydraulic resistance by virtue of the vortex chamber. The optimum design gives Mosbaek’s roof drain unique braking effect, which therefore has the greatest orifice openings and thus less risk of blocking. In operation, the orifice openings are unchanged.


Roof drains with regulation are mounted in depth points and gutters, and the catchment area can be up to 150 m2 per downspout.

When it rains water stow around the roof drain, which is therefore partly submerged when in operation.

The roof drain can be equipped with an integrated overflow.

The roof drain is surrounded by a fence at a safe distance from the inlets allowing the inflow of water from all sides and from above. When the brake is mounted on flat roofs, the inspection and service can be done under maximum hygienic and working environment conditions.

Often the roof drain can be fitted to existing or planned flat roofs. Roofs are usually prepared for 100 kg/m2 snow load, which is equivalent to 100 mm of water.


  • Regulates the discharge by means of centrifugal power in the vortex chamber.
  • Large orifice opening, which is unchanged during operation.
  • No moving parts.
  • No electrical parts.
  • Manufactured in acid resistant stainless steel AISI 316L (Werkstoff 1.4404).

The properties reduce the cost of construction, operation and maintenance.