Home furnishings retailer Dunelm kept up its impressive performance through the first half, but warned it will become 'much more difficult' to sustain like for like growth over the next six to twelve months.The group, which operates 100 shops including 88 of out-of-town superstores, reported like for like (LFL) sales up 15.4% in the 26 weeks to 2 January after a 15.1% rise in the 17 weeks to end October. Total sales jumped 26% to £254.2mToday's numbers included eight days' trading from the winter sale, traditionally the busiest trading days of the year, whereas only two days of the winter sale fell in the first half last year. Dunelm expects this has contributed about 2 percentage points to LFL growth over the half year and some 4 percentage points in the second quarter.Adjusting for the calendar effect, underlying LFL growth was 15.4% in the first quarter of the financial year and 11.6% in the second.Bosses said they remain cautious about trading in the second half as the calendar effect related to the winter sale will depress LFL growth by around 2 percentage points, while the year-on-year benefit of competitor withdrawals will pass and slow economic recovery will subdue consumer spending. There'll also be tougher comparatives next time round.'Looking ahead, it will become much more difficult to sustain like for like growth over the next six to twelve months,' said chief executive Will Adderley. 'However we have a strong pipeline of new stores coming through so I am confident that our overall business will continue to grow and to become stronger.'Interim results are due on 25 February.