UK housebuilder Persimmon painted an upbeat outlook on Tuesday, saying that it was "encouraged" by the level of customer confidence in the UK housing market with forward sales up 12% on last year.However, the company, which is the largest listed housebuilder in Britain, said it continues to experience planning delays when opening new development sites.Persimmon said in a third-quarter trading update that it has experienced a return to "a more traditional seasonal pattern in customer activity this year" as reservation rates have increased in the autumn after some slower weeks over the summer.The company is now fully sold up for 2014 with limited further stock availability for the current year. However, it has £696m of forward sales reserved beyond 2014, up from £622m at the same point last year.Selling prices are said to have stayed "robust" with growth seen in areas of higher demand, while cancellation rates are running at historically low levels.However, the company said: "Despite the ongoing improvements to the planning system, opening new development sites without undue delay continues to be one of the industry's main constraints."Whilst we have successfully opened 80 of the 100 new sites planned for the second half of the year, our desire to modestly increase our overall outlet numbers remains a challenge."Persimmon said it remains confident of growing group operating profits in the second half, helped by improved margins and cost control.The stock was 0.7% lower at 1,448p in early deals.