The company said industrial markets in North America were expected to remain "challenging", and in the UK the heating business "is expected to remain very competitive with little growth".
It said underlying revenues for the six months to January were set to grow 4%, down from an earlier forecast of 6%.
Wolseley also reported a 25% fall in full-year profits.
For the year to 31 July, pre-tax profits fell to £508m from £676m the year before, with like-for-like revenues up 7.1%.
The profit figure was hit by a one-off charge of £238m, mostly related to the write-down of assets at its Nordic business.
Wolseley's US operations account for three-quarters of its profits, and chief executive Ian Meakins said its plumbing supplies business there, Ferguson, had enjoyed a "great performance" with like-for-like revenues up 9.6%.
However, he added: "We continue to face some challenging markets in the rest of the Group and remain focused on improving growth rates and protecting gross margins whilst keeping the cost base tight."
In the UK, the company said trading related to new house building was "strong", but repair and maintenance business "remained weak" in the second half of its financial year.
Wolseley's shares closed down more than 12% at £36.58.
Shares in plumbing supplies firm Wolseley have dropped more than 12% after it cut its revenue forecasts.