It used to be that anyone who was building a log cabin was planning to use it for a vacation retreat, but manufacturers say that is no longer so.

Log homes are becoming popular again and and many of them are being used as primary residences.

Professional Builder magazine noted recently that as many as 125 companies are producing log home "packages" in the United States and Canada, shipping upwards of 30,000 units a year. One company has more than doubled its dollar volume since 1975.

Prospective buyers -- usually lot owners who hire contractors to put the packages up -- can chose from a wide range of kits.

Depending on who you deal with, you may be getting just the logs, a shell with or without floor, windows and roof, or a complete package. At least one distributor in the Washington area lets you pick the model and custom features you want and he builds it.

One important thing to consider is the type of log you're buying. Some manufacturers sell a full log seven to 10 inches thick. Others offer half-logs averaging about four inches, or some other fraction of the log. Most of the time, one side of the log is flattened off to make a smooth surface for your interior wall, in the event that you don't plan to add additional wall insulation.

For a full-time home in the Washington area, this usually isn't practical. An eight-inch white cedar log, for example, offers an Rvalue of 10. If you're using oil or gas heat, your supplier will probably recommend R-13 in your walls. If you're using electric heat, the power company may recommend R-19.

This means you'd be wise not to use the inside of the log as your interior wall, but instead to add furring strips and insulation, and then finish off with paneling boards. (Depending on electrical codes where you live, this may be necessary anyway to provide a place to run your wiring.)

Some manufacturers say the extra wall insulation isn't necessary. They maintain that their kits build such tight houses that you can use the log as the interior wall and actually save money on your heat bills over a conventional house of the same size.

In some cases, depending on what is offered, this may be true. But be careful.

"An R-11 wall properly installed and infiltration proof is probably better than an R-19 wall not properly installed," said Lee Fisher, director of industrial engineering for the National Association of Home Builders Research Foundation.

The catch is that the insulating capacity of the walldepends on who builds it and how well, in addition to what materials go into it. It never hurts to put in the amount of insulation your heat supplier recommends.

Many people are lured into the log home market by the prospect of low prices, but again, it depends what you buy. Full logs are more expensive than split logs. Cedar logs can cost 20 percent more than some other kinds. Extra insulation may not be part of the package. A deceptively inexpensive kit may not include all that a costlier one does.

Some dealers feel that they've been a disservice by publicity that has stressed only price. Barney Burke, the regional distributor for Boyne Falls Homes, says that he recently received more than 100 inquiries after an article appeared extolling the low cost of log home packages.

"But we're probably at the top of the line as fare as log houses are concerned," he said of his white cedar packages. "We've built houses in the $40,000 to $160,000 price range. We're looking for the buyer who wants a quality product with low maintenance and upkeep."

Low price, in other words, is not the only consideration -- or the main thing many dealers are selling.