The firm started redundancy consultations late last month but has now decided to shut plants at Creetown and Killoch.
A Barr spokesman said: “With the construction industry as a whole continuing to face severe challenges and the consequential demand for structural steel plummeting, trading at Solway had become increasingly demanding.
“The company announced it would be carrying out a review of the entire steel business in December but, with little prospect of trading conditions improving, Barr Limited has had to take the difficult decision to scale down and close the manufacturing facility.”
One worker told the Dumfries & Galloway Standard: “There’s no way out and they’re not going to be tendering for work so everyone – directors, the drawing office, the steel workers – is out of work.
“They won’t be putting in for any more work, we’ll be finishing what we’ve got to do and that will be it.”