As a single mother and business owner, Shelly Trisler is used to dealing with challenges. In her four years running First Choice Flooring in San Marcos, Trisler has gone through a divorce, worked 60-hour weeks and found her warehouse being used as an illegal drug laboratory.

But a slowing North County housing market could be more than Trisler can handle. The recent drop in North County housing sales and new housing construction has cost her $850,000 in residential flooring business since January, a 35 percent decline in sales compared to the same period last year.

The slowdown threatens to shut down First Choice Flooring for good.

"We haven't seen it this bad in 10 years," she said. "I'm considering selling it because of the market."

Trisler's First Choice Flooring is one of several businesses feeling the chill of the "cooling" housing market.

Sales of existing homes are down 33 percent and applications for new-home construction permits are slowing sharply. The declines are causing sales to drop at many local businesses that supply residential housing with products from carpets to sod for front lawns.

Other, similar business have been hurt financially as customers chose less expensive products to meet their home improvement needs. Still others have avoided the up-and-down cycles of residential housing by diversifying their business into other markets.

Cees Molenaar works for an organization that represents 145 trade companies, such as carpenters and electricians, tied to the housing industry.

"Everybody is feeling it," said Molenaar, executive vice president for the California Professional Association of Specialty Contractors' San Diego chapter. "They just have to weather the storm."

Dick Marsala, a salesman for Direct Carpet Sales in San Marcos, said sales at his store are down at least 35 percent from last year.

"I can't figure it out," he said. "The economy's supposedly great and people are working."

In many cases, North County residents are still buying home improvement products, but they are buying more affordable ones than they might have last year.

Coussaie Agha, a salesman at Carpet Country Flooring in Poway, said his company's sales are lower because customers are ditching the more expensive hardwood floors and buying lower-priced carpeting instead. But Agha is optimistic about the future.

"Customers have scaled back as far as what they are doing," he said. "We expect it will pick up again in January or February."

An Encinitas home decorations store owner, who didn't want to be named, said store traffic has dropped from about 500 people per day three years ago to 10 today.

"People are scaling down," the owner said. "We aren't the first thing on their list."

Two years ago, Tony Lawson could see what a housing construction slowdown would do to business at his landscape architecture firm, A.D.L. Planning in Carlsbad. So he switched his focus from residential housing to public works projects, such as parks and road beautification.

"I've been through too many roller coaster rides with it," Lawson said about working with housing projects.

Stephen Copley, a landscape architect and owner of Copley Design Collaborative in Oceanside, is trying to do what Lawson did. He said the residential housing market is just too volatile. Housing-related orders are 75 percent of his business, he said, while public projects, such as parks, are 25 percent.

"I'd like to reverse those numbers," he said.

But the housing slowdown isn't bad news for all North County businesses. Ken Brown, a sales consultant for CalSpas in San Marcos, said sales of spas, hot tubs and barbecue equipment are up from last year. He said some weeks in October have seen business double compared to October of 2005.

Brown attributed the sales spike to people investing in their current home instead of buying another one.

"They are staying with the homes they already have," he said.

Both home sales and sale prices have declined in September, the most recent figures available, compared to September 2005.

The number of single-family detached homes sold in North County dropped by more than one third, to 662 in September from 926 in September, 2005, according to the North San Diego County Association of Realtors.

As sales declined, area housing prices declined with them. The median price for an existing North County single-family detached home dropped $5,000, to $620,000, from prices in January, according to the association. Although it is only a 1 percent decrease, it comes after year-end home price increases of more than 3 percent in 2005 and 16 percent in 2004.

Also, North County homes are staying on the market longer. The median number of days that a North County single-family home was on the market increased from 41 days in September, 2005 to 58 days in September. The figures don't account for home sellers who pull their homes off the market and then put them back on at a later date, one economist said.

Construction of new homes is also slowing. For the first nine months of 2006, only 3,910 building permits were issued in San Diego County, down 41 percent from the 6,672 permits issued for the same time period last year, according to the Construction Industry Research Board. Developers must get building permits before constructing new homes.

Alan Nevin, who studies residential construction and housing for MarketPointe Realty Advisors in San Diego, said building permits are down because home building companies aren't going to start new residential housing projects until they sell the current homes under construction. He said the situation is going to get worse before it gets better and predicted the home sales slowdown would continue for another year.

"Our permit count in the fourth quarter is going to be really dismal," Nevin said.

It is the dismal state of the housing industry that has caused Shelly Trisler to want to sell First Choice Flooring. Until then, she keeps her head high and tries to keep First Choice afloat until she can find a buyer.

"Put this in there," she said. "This business is for sale. Shelly is done."

Contact staff writer Patrick Wright at (760) 739-6675 or pwright@nctimes.com.