Why not the catalogue roughness?

DIN 1986-100 accounts for deposits with kb = 1.0 mm. The smaller material roughness stays visible only as a reference.

What applies to a stack?

Table 11, branches without an inner radius, main ventilation: DN 60 0.5 l/s, 70 1.5, 80 2.0, 90 2.7, 100 4.0, 125 5.8, 150 9.5, 200 16 l/s.

Which DU values do the urinal and shower use?

Urinal with flush valve DU 0.5, urinal with cistern DU 0.8, shower without a plug DU 0.6, shower with a plug DU 0.8.

Why is a WC at least DN 100?

The largest fixture sets the minimum nominal size. A WC of DU 2 requires DN 100 even when the calculated flow would be smaller.

Plumbing

Drainage

Discharge

2,00l/s

100

Velocity

0,65m/s

Drainage finds the waste-water discharge to DIN EN 12056-2. Fixture units and the frequency factor give the volume flow. Nominal size is then chosen together with the gradient and the pipe material.

Discharge

2,00

l/s

Nominal size

100

Litres per minute: 120,0l/min
Fill height: 39%
Velocity: 0,65m/s
Limit h/d: 3,10l/s · 50 %
Sum DU: 3,1
Minimum DN: 100

Operating roughness kb = 1.0 mm (DIN 1986-100) Material k = 0,10 mm, reference only. Part fill h/d = 0.5.

Input

Pipe section

Pipe

Use

Washbasin

DU 0,5 · min. DN 40

Shower

DU 0,6 · min. DN 50

Shower with plug

DU 0,8 · min. DN 50

Bath

DU 0,8 · min. DN 50

Kitchen sink

DU 0,8 · min. DN 50

Dishwasher

DU 0,8 · min. DN 50

Washing machine

DU 0,8 · min. DN 50

WC 6 litre

DU 2,0 · min. DN 100

Urinal (flush valve)

DU 0,5 · min. DN 50

Urinal (cistern)

DU 0,8 · min. DN 50

Floor drain DN 50

DU 0,8 · min. DN 50

Gradient

Continuous discharge

l/s

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How it's calculated

Waste-water discharge follows DIN EN 12056-2: Qww = K times the square root of the sum of fixture units, at least the largest single unit, plus a continuous flow. A branch and a collecting pipe inside the building are sized at a part fill of h/d = 0.5, and a buried pipe outside at h/d = 0.7. The calculation is Colebrook-White with the operating roughness kb = 1.0 mm for every material. A stack uses the allowed flows of Table 11 for main ventilation, not the part-fill formula. The minimum nominal size of the largest fixture still applies.

Worked example

HT DN 100, 1% gradient, half full: limit 3.10 l/s. The same pipe at h/d = 0.7 carries 5.19 l/s. A stack at 2.20 l/s needs DN 90 with Qmax 2.7 l/s.

FAQ

Why not the catalogue roughness?: DIN 1986-100 accounts for deposits with kb = 1.0 mm. The smaller material roughness stays visible only as a reference.
What applies to a stack?: Table 11, branches without an inner radius, main ventilation: DN 60 0.5 l/s, 70 1.5, 80 2.0, 90 2.7, 100 4.0, 125 5.8, 150 9.5, 200 16 l/s.
Which DU values do the urinal and shower use?: Urinal with flush valve DU 0.5, urinal with cistern DU 0.8, shower without a plug DU 0.6, shower with a plug DU 0.8.
Why is a WC at least DN 100?: The largest fixture sets the minimum nominal size. A WC of DU 2 requires DN 100 even when the calculated flow would be smaller.