New owners Graham Hood and Sean Egan are simplifying the previous board structure to reduce the number of directors.
Former chief executive Dugdale will retire at the end of the year as the business which operates nationwide and turned over £12m last year prepares to deliver record revenue.
The firm counts Willmott Dixon, Kier and Morgan Sindall among its clients and has delivered several major schools in the south east among a wide portfolio of projects.
DES began implementing a change plan 12 months ago to enable a smooth transition, which will see Dugdale continue to support the business in a strategic capacity.
The restructure coincides with the launch of DES Energy, which will help clients reduce their energy spend.
“We have an excellent team with a diverse range of skills that complement each other well,” said Egan.
“We are looking forward to embarking on a new chapter for DES and our supply chain.”