Marketing manager Sara-Jane Johnson said the 3,200m2 extension was on course to be completed by 1January.
The firm currently has 203 staff working across its three sites, which include a 10,000m2 warehouse in Northampton and a sales and design office in Watford.
Production at The Print Factory has been unaffected by the work and the company will only close on Christmas Day during the holiday period.
Johnson said the firm had recently secured contracts from three unnamed major clients, which could lead to an increase in staffing levels in the new year.
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