Markit Economics said the sector's PMI climbed from contraction to expansion for the first time since October 2012 with a push from residential building work, which reached the fastest pace in more than two years.
The headline index rose from 49.4 in April to 50.8 in May. A PMI score higher than 50 indicates business is growing while less than that indicates business shrinking.
Markit said the index shows "only a marginal pace of expansion." The headline index also remained at less than its long-term average of 53.9, the firm said.
"U.K. construction output appears to have finally pulled out of a tailspin in May, but the latest figures suggest that the sector is worryingly reliant on residential building work for thrust," Markit Senior Economist Tim Moore said.
While residential construction projects rose, "shrinking spending on both commercial and civil engineering projects acted as a drag on overall new business growth," Moore said.