James Latham's revenues rose to £107.3m in the six months to the end of September - 7% up on a year ago.
The group said it had seen volumes continue to grow especially through its own warehouses where they were up nearly 8%.
Chairman Nick Latham said: 'The cost price of our products overall continues to increase in comparison to the comparative six months.
'This is in part down to the weakening of sterling following the European Union Referendum, but also in this six months we have seen manufacturers increasing prices, and we have not been able to pass all these increases onto our customers.'
Gross margin was 17.3% compared with 18.7% in the comparative six months.
But Latham said this was similar to the 17.6% achieved in the second half of 2016-17, and he believed margins were starting to stabilise.
Pre-tax profit fell by 12.2% to £6.7m and earnings per ordinary share were 27.8p (2016: 31.2p) a decrease of 10.9%.
The board has declared an interim dividend of 4.5p per ordinary share (2016: 4.5p), which is covered 6.2 times (2016: 6.9 times).
At 9:04am: (LON:LTHM) Latham James PLC share price was -102.5p at 842.5p