How do you size rainwater pipes on a Borama building?

Rainwater pipe sizing in Borama is a calculation that decides whether a roof drains in the Gu rains or backs up into the gutter. When supervision on a site is thin, that calculation can be skipped and the downpipe diameter chosen by eye. The failure appears only in heavy rain, long after the pipes are buried in a wall.

How do supervision gaps turn into a pipe sizing error?

A sizing error survives because nobody stands at the wall with the drawing while the pipe is fixed. The designer works out the flow from the roof plan area and the rainfall intensity for the site, then picks a diameter and a fall. On a busy site, the plumber may fit whatever pipe the merchant has in stock, and the supervisor signs the day's work without measuring it. Borama's rainfall arrives in intense bursts, so a pipe that is one size small can handle a drizzle and still overflow in a downpour. Ask the project's engineer for the design calculation and check that the diameter on the drawing matches the pipe in the wall. If no calculation exists, that is the gap.

What should a supervisor measure on site?

Measure three things: the roof plan area that drains to each outlet, the bore of the downpipe, and the fall along the gutter to that outlet. General practice ties the pipe size to the roof area it serves, with the manufacturer's flow chart or the project specification giving the number, so confirm the limit against the specification or the engineer rather than a rule of thumb. While the wall is open, look for the pipe bore and check it against the drawing. Then check the gutter fall with a level; standing water in a gutter after rain points to a fall that is too flat or a pipe that is too small. Count the outlets against the roof shape. A long roof drained by one outlet concentrates the flow, and two outlets cost little more than one.

What does overflow during rainfall tell you afterwards?

Water staining on the wall under the gutter, damp plaster at the pipe entry, or a wet patch at the base of the downpipe after rain all point to the same problem. The hard part is timing. By the time the Gu rains show the fault, the pipe is often boxed into the wall and the client owns the repair. Ask for the test records: a simple flow test before the pipe is covered, or a hose run over the roof while the wall is still open, gives a warning while the work is accessible. Record the pipe diameter, the roof area and the date of the test. When a client reviews a low bid, the missing item is often this supervision time, and the pipe sizing check is one of the first tasks dropped.

What to do next

Before the next pipe is fixed, ask the site engineer for the roof drainage calculation and the downpipe schedule, then measure one downpipe bore and the gutter fall yourself. Write the figures into the site diary with the date. Where the drawing and the pipe disagree, stop the fixing and ask the project engineer to confirm the correct size in writing.