A home inspection/engineering service is warning consumers that termites are on their way back as a hazard to your home's health.

Criterium Engineers, based in Portland, Me., says chemicals currently being used on the pests are not strong enough to keep the wood-eaters down for long and that special care needs to be taken to make sure the chemicals are effective at all.

"For the last 40 years or so, termite control had been effective and commonplace. Concern about termites in new homes had basically disappeared," said Criterium President H. Alan Mooney in the current issue of "At Home."

He said effective pesticides such as chlordane were used to treat the soil prior to finishing the foundation of a new home, which virtually sealed it from termites.

"However, in 1988, the use of chlordane and heptachlor, the most common termite soil treatment chemicals, was stopped due to concerns about environmental and human health effects," Mooney said. "The pesticides that have replaced chlordane and heptachlor are considered more environmentally acceptable and less risky, and they are also less effective."

According to Mooney, when properly applied, chlordane and heptachlor could be effective for more than 30 years. Currently available chemicals, when applied in similar strengths, last only five to seven years. He also said the new materials are somewhat harder to apply correctly.

"As a result, termite control needs more attention than ever," he said.

One of the best ways for builders to keep termites under control is to not allow them into dwellings in the first place.

For instance, keeping exterior siding and insulation between 6 and 18 inches above the ground prohibits termites from crawling up and finding a secure environment in the home.

Mooney also suggested that all wall and ceiling slab penetrations be sealed, as well as the junctions at the main floor slab with any adjacent floors or patios. He suggested that plastic or other non-cellulose materials were most effective.

He also recommends that hollow cells in concrete foundations should be capped, and crawl spaces should be well ventilated to keep them dry.

All wooden floors, decking or porches should be elevated on concrete piers, posts or stirrups, he said.

Although declining to specifically name good chemicals that could be used, Mooney said that to be effective the chemical barrier must penetrate evenly and then bind to the soil particles.

"It must be durable," he said. "The objective is to establish a continuous horizontal and vertical barrier between the wood in your home and the termites in the soil."