Building through the rainy season

The rainy season is not a reason to refuse to build. It is a reason to decide which tasks are allowed to be open to the sky. Lagos, Abuja, and Ibadan do not share one calendar, even though all three are wet for a long stretch of the year. Programming a site in Lekki with a slogan you heard about harmattan in Abuja, or programming Kubwa with a Lagos “August break”, is how materials are wasted.

Three calendars

Lagos, from published averages, is wet from about April to October and drier from November into March. The same tables put the yearly total near 1,550 millimetres, June near 290, August near 70, and September back above 200. A study of NiMet daily records for 1990–2017 found a mean onset around 27 March and a mean cessation around 4 November. The light August is the famous little dry season on the western coast. Use it to close a roof or to cast a slab you can protect. Do not use it as a promise that the formwork can sit uncovered until an inspector is free. September is wet again.

Abuja’s summaries describe rains from April to October, about 1,400 millimetres a year, and months from May to October that each pass 100 millimetres. The city is higher and inland. It does not get Lagos humidity in the same way, and it does get harmattan dust once the rains retreat. In 2021, NiMet’s director-general told reporters that a late ending, into November, had been forecast for Abuja and was not a new miracle. A February 2026 short-range outlook still listed dust haze over the north-central region at the start of March. So the Abuja year is a long wet middle, a dusty dry, and a hot late dry season. Painting and fair-faced concrete care about the dust. Excavations care about May to October. The same calendar lands differently in Gwarinpa, Maitama, Kubwa, and Lugbe: estate drains, a formal frontage, or a long haul for materials. The Abuja hub is the overview.

Ibadan’s NiMet-based study put mean onset at 29 March and the mean season length near 200 days. Ignore the paper’s conflicting cessation dates and watch the forecast instead. What the city has already shown is intensity. On 26 August 2011, about 187.5 millimetres fell in a few hours, Eleyele overflowed, and floodplains and hillsides flooded. An “average month” is a poor description of an Ibadan afternoon. Trenches at the bottom of a slope in Mokola, Agbowo, or anywhere above the Ogunpa, Ona, or Ogbere should not be left open because the morning was sunny.

Tasks that can proceed, and tasks that should wait

Work that can continue in the rains, if the site is organised: block laying under a finished roof, internal services, plaster in rooms that are dry, fabrication that happens off site, and excavations that are pumped and closed the same day. Work that should be timed: deep trenches, pad foundations in sandy Lagos ground where the hole becomes a well, uncapped hollow blocks, a slab with no cover, and a roof sheet delivery that sits in mud until the carpenter returns.

Hollow sandcrete blocks drink. The National Building Code’s curing advice — keep them wet under cover, do not rush them into the wall — is the opposite of leaving a pallet in a June yard and building with them at dusk. Wet blocks in a wall are heavy and weak. Cover the day’s work. Turn the last course so rain does not pour into the cores. Lead temporary water off the slab, away from the footing you cast last week.

Lagos coastal sites add groundwater. A hole that was dry at 7 a.m. in Lekki can be unusable by noon, not because the sky opened but because the water table and the tide of the lagoon system are not impressed by your programme. Pumping is a method, not a personality. If the investigation said the ground was weak, believe it when the spoil looks like soup.

Site drainage is part of the building

The building’s permanent drains and the site’s temporary drains are different systems, and both matter. Before the first block, decide where stormwater goes this week. Pumping into a neighbour’s compound is how projects grow enemies and, in cities that are already flooding, how they grow enforcement. Lagos has major public drainage works precisely because plot water becomes street water. Ibadan’s flood project exists because channels and waste-filled culverts could not pass a storm. Abuja’s master-plan setbacks exist so a private roof does not become a public problem.

Store cement on pallets, under a roof, off the wall. Store reinforcement off the mud. In Abuja’s dry months, add a cover against dust, not only against rain. Electrical fittings left in an open carton in Lagos humidity are a renovation you will pay for during the original job.

People and the forecast

NiMet publishes seasonal guidance and short outlooks. A site supervisor who never looks at them is guessing with your cement. Give someone the job of calling off an open pour when the afternoon storm is already on the radar. In Ibadan, the state’s own flood advice after 2011 included the plain instruction that people near rivers should move upland if rain persists. A construction crew is not exempt from that. Do not keep excavating a stream setback because the concrete truck has arrived.

Labour plans should assume lost afternoons in the peak months. A programme that needs every day of June to be a full day on an open Lagos site is a story, not a programme. Build the float in. The float is one of the real cost drivers, and it is cheaper than recasting a washed-out footing.

What to tell the quote

Say the month you hope to start, whether the plot has flooded, and whether the roof of an existing house is already on. A renovation can hide indoors. A new build cannot. Micheletti Construction Limited would rather hear “we want to cast in March” in November than hear it on the morning the trench is full. Choose the city on the form so the follow-up uses the right calendar. The forecast is NiMet’s, and the building judgement happens after you send the request.