Construction industry leaders have called on the Northern Ireland executive to devise an urgent long-term plan for wastewater infrastructure, warning that a lack of capacity is choking off housebuilding, pushing up rents, and harming the environment.

Only 5,900 homes were built in Northern Ireland last year, the second-lowest figure in a decade and less than half the number recorded in 2005. Build Homes NI, which represents major developers, says the slowdown is contributing to the fastest-rising rental and housing costs in the UK and is driving some firms to abandon the region for projects in Great Britain or the Republic of Ireland.

Paul McErlean, the body’s director, said the failing wastewater network has far-reaching effects. He pointed to long social housing waiting lists, rising pollution in loughs and rivers, and blocked economic development. Mr McErlean described the situation as a system-wide crisis that demands a long-term solution, but said two years after the return of devolution there is still no executive plan to address what he called chronic underfunding of NI Water.

NI Water frequently objects to new planning applications because the existing sewer network cannot handle additional demand. In the greater Belfast area, an estimated 17 million tonnes of untreated or partially treated wastewater is discharged into Belfast Lough each year. At the start of 2025, Stormont budget cuts halted planned upgrades to treatment plants in Belfast, Holywood, and Newtownabbey, as well as an extension of the city’s underground storm tunnel. Without those works, four treatment works around the lough are projected to breach compliance legislation within 12 months.

Build Homes NI has written to the leaders of Northern Ireland’s main political parties asking them to meet urgently and agree a long-term sustainable funding solution. Mr McErlean said that costed proposals already exist and that securing a resolution would show that devolved government can deliver for society.