Housebuilder Berkeley Group revealed losses of up to £3m since May and expects the figure to leap to £5m before the end of April 2001 because of delays caused by bad weather.
Berkeley chief executive Tony Pidgley said: "The sites are slurries. It plays havoc with our programme and our costs."
He added: "We have this little car park that has been sitting there for six weeks waiting to get finished, because we can't lay the material that seals the surface, because it pits in the rain."
Federation of Master Builders' director-general Ian Davis said plumbers and general maintenance contractors were in strong demand in flood-damaged areas, but were hampered by bad weather and a shortage of skilled workers.
He said: "I was talking to a plumber last night who was scrapping his planned two-week Christmas holiday so that he could catch up."
Building materials producers also said site delays were hurting short-term demand.
Wolseley chairman Richard Ireland said: "It's always quiet at this time of year, but for many site staff the Christmas holidays appear to have started early." Ireland said the recent wet weather was having an adverse impact on major sitework.
Beazer managing director Nick Smith said sites in the North-west, South, South-west and South Yorkshire had been badly hit.
Among small and medium-sized firms experiencing problems, New Forest-based housebuilder Emlor has been badly affected. Since work started on one project in September, the firm has completed only three foundations instead of the 15 it would usually expect to install.
Emlor Homes director Spencer McCarthy said: "The delays will cost us because it is holding up the programme and we need to get the houses up for spring to sell." Borras Construction managing director Ray Borras said he was focusing on tenders that involved internal refurbishment.
He said: "Frankly, it is hard to plan anything. We have got an inevitable drift on all external contracts. But I am getting all my carpenters together to build an ark."