The halls we're decking keep getting larger. In 1978, the average single-family home was 1,750 square feet. In 2006, it was 2,456 square feet. And as rooms expand, so do their components: Ceilings are higher, fireplace mantels bigger, stairways longer.

All this means that, come the holidays, there's more real estate to decorate. Christmas has been supersized - bring on those bigger boughs of holly!

"For years, the tallest tree in the permanent-tree industry was 9½ feet," says Jim Kuser, visual merchandiser at Waterloo Gardens. "But with larger houses, people demanded 12- and 14-foot trees."

In New Hope, Kim Earley's two-story foyer gets the holiday treatment with live poinsettias running up the stairs and arranged under the entrance table, fresh cedar garland wrapped around the banister, and Byers' Choice Carolers in clusters of three or five for maximum impact.

"I decorate the entire first floor of the house, and sometimes even the finished basement," Earley says.

She also relies on masses of candles for effect: "I use pillar candles accented with ribbon on large candlesticks on the mantel, and I surround them with fresh greens strung with lights."

Because of the distinct challenges large houses present this time of year, we sought guidance from the pros on scale, scope and some other dimensions of holiday decorating.

The tree. Size matters. In a room with 20-foot ceilings, a 6-foot tree, the standard size, looks, well, dinky. And size also bears on the perennial question: fresh or artificial? Purists must have fresh, and a big fragrant tree certainly makes an impact, but there aren't many live trees over 12 feet readily available.

Larger trees mean more lights, of course - often lots more. If you must have a fresh tree, plan to use at least 100 lights per foot of tree. But you can forget about tangled light strings and burned-out bulbs if you go with one of today's "permanent" (that's artificial to you and me) trees. Many come prestrung with lights guaranteed to burn for at least 3,000 hours. And when one light goes out, the rest stay lit.

Tall, prelit artificial Christmas trees are available through a variety of high-end mail-order catalogs, but the widest selection may come from a company called Treeclassics.com. Owner Leon Gamze says sales of trees 12 feet and taller have increased 20 percent a year over the last five years. His company's largest ready-to-ship artificial tree is 20 feet tall, prelit with almost 11,000 lights, and costs about $7,000.

With any big tree, this is essential: You can't trust it to stand by itself; it needs securing.

"Sometimes people forget to wire the tree and they load the front with decorations and the weight pulls the tree over," Kuser says. "People should remember to decorate all the way around, to balance the weight."

Wire that tree to the wall in two places: halfway up and again at the top. Attach the wires to the wall by screwing eyehooks into a stud. Or, if the tree is tall enough, wire it to a nearby stairway or to the ceiling.

For very spacious rooms, consider using several trees. Or supplement the primary tree with "pencil trees" - 6½ or 7½ feet tall, but narrow. Use them to flank a fireplace, either free-standing or in urns for additional height and drama.

Ornaments. Christmas decorations are on steroids. Even standard 6- and 7-foot trees are now festooned with decorations the size of grapefruits.

"As houses get bigger, the trees get taller, but we have to keep in mind the decor that goes on the tree," says Donna O'Brien, floral designer and owner of Beautiful Blooms on North Hancock Street. "The tree now needs to have even more ornaments so it doesn't look sparse. And the tree should show the personality of the house, but also our own personalities."

A standard Christmas ball is 3 inches in diameter, Kuser says. "Go bigger than that. And use a bigger star, finial or angel at the top of the tree. Our signature style [at Waterloo Gardens] is to put a floral bouquet at the top, which is especially effective on bigger trees."

For large trees and large spaces, use ribbon that's two inches or wider. O'Brien recommends ribbons made by Midori, available at Details on South 18th Street or the Papery on North Third Street.

Wreaths and garlands. Whether fresh evergreens or artificial, garland comes in 6- or 9-foot lengths. For a large stairway, go with a bushy garland - prelit, of course - with "picks" (decorations on a stick) inserted in sections, Kuser suggests. O'Brien recommends decorating a mirror with garland all the way around, to create a new frame, and then hanging a wreath over it.

With the fireplace, don't be subtle. "On a mantel, pack away what's there and replace with garland, tons of candles, and apothecary jars or vases filled with balls or ornaments," O'Brien says.

Standard-size wreaths are 12 to 15 inches in diameter. Large is 24 inches or more, and massive wreaths start at 48 inches. O'Brien likes to double up wreaths for additional impact. "I also layer them on top or inside of each other," she says.

Other decorations. Hanging large ornaments from ceilings, in windows, or from light fixtures is a strategy worth considering. Macy's carries giant red or silver glass kugel (German for ball) ornaments from the Martha Stewart Collection. At more than a foot long, they're not meant for the tree. And if glass balls don't entice, you can find huge snowflakes, icicles or stars.

A bigger home means more space for collectibles - but that means you need lots of collectibles to make an impact. Whether it's nutcrackers, carolers or Santa figures, cluster your collection in one spot rather than spreading it around. Have an empty corner? Fill it with tall candleholders that sit on the floor.

For sheer volume, Kuser says, you can't beat faux poinsettias everywhere: on wreaths, garlands and the tree. Those big flowers take up a lot of space. (O'Brien prefers her poinsettias alive and white versus the standard red. "I like their simple, clean elegance.")

Dress up your chandeliers by changing to (or adding) lampshades that are gold or beaded. Add crystals to what's already there, to catch more light. Accent with a green garland, and hang glass balls.

Or drape crystal garlands and icicles liberally. Since they're not associated with any particular holiday, they can stay up until February.