UPDATE 1-Travis Perkins sales hit by poor summer weather

* Trading in-line with expectations

* Q3 Total LfL sales per trading day down 3.5 pct

* Q3 total sales down 2.4 pct

* Trading improved in Sept, on target to meet market expectations

* FD Paul Hampden Smith to step down in Sept, 2013 (Adds details)

LONDON, Oct 12 (Reuters) - British builders' merchant and do-it-yourself retailer Travis Perkins posted a 3.5 percent decline in underlying sales after poor weather and tough competition crimped trading in its third quarter.

The firm, whose brands include City Plumbing, Keyline, Tile Giant, BSS and Wickes, on Friday said like-for-like sales in the period to September 30 were down in all but one of its four divisions, although sales had improved at the end of the quarter, with plumbing and heating boosted by colder weather.

Third-quarter turnover at builders merchant depots open more than a year fell 1.6 percent and was down 4.7 percent at its plumbing and heating unit. Like-for-like sales were down 7 percent at its home improvement business, while its specialist merchanting division posted a 1.3 percent rise.

The group said it remained in line to meet market expectations, although it had increased its cost management to help ease margin pressure across its merchanting divisions.

Though both construction and consumer markets have been weak in the economic downturn Travis Perkins has performed relatively well. In July the group posted a 7.3 percent rise in first half profit despite taking a 10 million pound hit due to record rainfall disrupting activity at building sites.

British construction activity, not helped by a spate of flooding across the country, contracted for a second straight month in September as business morale held close to its lowest since entering recession in 2008.

Travis Perkins, which also said on Friday its finance director, Paul Hampden Smith, would step down next September, is expected to post a full-year pretax profit of 309.5 million pounds according to a Reuters poll of 19 analysts.

Shares in the FTSE 250 firm closed at 1135 pence on Thursday, up 35 percent on a year ago, valuing the business at around 2.7 billion pounds.

(Reporting by Neil Maidment; Editing by Paul Sandle)

((neil.maidment@thomsonreuters.com)(+44)(0)(207 542 2292)(Reuters Messaging: neil.maidment.thomsonreuters.com@reuters.net))