The merger, which takes effect on 1 May, is to create a firm with a UK turnover of £65m.
DL&E partner Alistair Collins said none of the merged firm's competitors had a comparable division. He said: "It's an industry leader. It's quite a coup." NBW Crosher & James' partners will become partners in DL&E, although the firm will continue to trade under its current name. The firm has 60 staff and a turnover of about £5m.
Collins added that the move was indicative of increasing activity in the consulting industry. He said: "All those in the market have peaked in terms of organic growth. So you can take the merger or acquisition route, and we prefer the merger route." DL&E merged with building services specialists Mott Green & Wall in 1999 and with specification writers Schumann Smith last year.
Senior partner Paul Morrell said: "The impact of taxation policy on property and construction clients becomes more pronounced and more complex with successive finance acts.
"NBW Crosher & James virtually wrote the book on strategic advice in planning ahead for this and we are delighted to be able to extend this creative advice to our clients in an integrated way."