Self-storage group Big Yellow said that 2013 has started well with trading patterns returning to normal following a seasonal weak festive period.The firm's third quarter (three months to December 31st 2012), its seasonally weakest, saw occupancy in its 54 wholly-owned stores fall by 139,000 square feet (4% of capacity), compared to a loss of 57,000 sq ft (1.7% of capacity) in the same quarter the year before."The group's achieved net rent per sq ft in this quarter has also reflected the introduction of VAT on self storage sales, as we shared the increase in cost arising from the introduction of VAT with our domestic customer base," Big Yellow said. However, it did say that the impact of this VAT introduction was as anticipated.Total store revenue for the 54 stores was £16.8m for the quarter, up 3.7% year-on-year, but down 9.7% on the second quarter."The introduction of VAT presented the group with a significant challenge and we are broadly satisfied with the way the business has absorbed this change," said Chief Executive James Gibson. "Although it is early in the New Year to have much visibility, January has started positively with a return to more normal trading and an encouraging book of reservations.  We look forward now to our seasonally busier period."