Southampton-based R&W Civil Engineering almost doubled turnover last year to £50m on the back of Smart motorway work in the south.
The firm, which is the largest operation within the Chantacre group, saw turnover jump from £26m in 2019 on the back of the M27 and M23 for BMJV and Kier respectively.
But pre-tax profit stayed around £1m due to a significant increase in subcontract expenditure that was required to deliver the rapid increase in turnover, placing downward pressure on margins.
Across the rest of the group, a £4.9m profit from the sale of R&W Traffic Management last December helped to keep the group in the black with pre-tax profit of £3.7m.
Group revenue rose 37% to £77.5m while staff headcount dropped by 140 to 313.
Among the other subsidiaries R&W Environmental grew 50% to just over £9m turnover generating almost £1m profit.
Local Dorset groundwork contractor R&W Langley grew revenue by 16% to just under £10m but suffered growing pains and broke even.
R&W Rail lifted revenue from around £0.7m to £3.8m, while returning a £0.8m loss because of higher investment in recruiting and mobilising teams.