Ulster Bank's seasonally adjusted monthly bell weather index for the construction industry registered its lowest reading in four years in August - down from 47.5 to 43.8.
The bank says weaknesses in the housing sector were exacerbated by what it describes as a 'surprisingly low activity in commercial and civil engineering works'.
The poor weather may have played a part in the third successive month of declining activity in the sector.
Employment in the industry has contracted for the fourth month in a row, with significant falls in August.
