AP PHOTO/MASTER CRAFT INSTALLATIONS

Today, many owners of older-style houses want the flexibility of an open plan. So they are knocking down walls to create that openness where none existed before.

If your home was built within the last decade, odds are it was designed with an open plan. The kitchen flows seamlessly into the family room, and few walls separate the living and dining areas.

But what if your home is a bit older? In the 1970s and '80s, "houses were built with a separate great room, separate small living room, separate small dining area" and a kitchen walled off from the rest, says Ellen Goode, professor of interior design at Meredith College, in Raleigh, N.C. Phrases like "formal dining room" and "breakfast nook" were selling points.

Today, many owners of those houses want the flexibility of an open plan, and are knocking down walls to get it.

Kitchens are frequently merged with other rooms to create a larger, more inviting family area. "The kitchen is the hub of the household," says Paul J. Zuch, president of the National Association of the Remodeling Industry. "Kids are doing homework ...momwants to keep an eye on the kids when they're on the Internet." Busy families are trying to spend time together when they're home.

Another reason why walls in older homes are coming down is because beds, sofas and other possessions are larger than they were a generation ago, says Dorcas Helfant, past president of the National Association of Realtors.

"We want big screens," she says, "and we need space to sit back far enough from the screen."

Knocking down a wall may seem pretty easy, and it can be.

But doing the demolition and rebuilding, and figuring out how to decorate the new combined space can be complicated, says Vern Yip, designer for HGTV's "Urban Oasis."

Planning is vital, he says.And as potential DIY projects go, this one is best left to a professional.

CHALLENGES AND COSTS

Demolishing awall doesn't have to be expensive or complicated, assuming nothing is hidden inside. But it's likely there is some mix of electrical wiring, heating ducts, plumbing, even sewer and gas lines snaking through the wall's interior.

Those items will need to be rerouted. And new electrical outlets will need to be installed elsewhere, perhaps in the floor, to make up for any that are removed.

Another potential cost: Walls originally built before 1978 probably have a base layer of lead paint.

Even if they've been repainted since then, the removal must be done in compliance with safety guidelines. A certified remodeler can test for lead, Zuch says, and remove it properly.

Most important, a load-bearing wall (which kitchen walls often are) will have to be replaced with architectural columns or some other type of support. So it's wise to have the wall assessed by an expert before doing any demolition.

In addition, there are costs that can't be measured in dollars and cents: With a flowing floor plan, noise is harder to contain.

DESIGN IMPLICATIONS

From a design perspective, knocking down a wall brings opportunity and a few hurdles.

"A home always seems much larger with fewer walls, even though you haven't expanded your exterior envelope," Yip says.

"You open the possibility of more natural light pouring into parts that previously couldn't access natural light."

But once a wall is down, "you don't have Space A separated from Space B, so it all needs to work together," he says. A kitchen and family room may both need to be redecorated if they're now connected.

Furniture can be used to delineate specific areas, but homeowners may not know how to accomplish that. "I see this all the time: I don't know where to put my sofa, don't know where to put my TV, because you've removed all your interior walls," Yip says .

Goode says partial-height walls or standing screens can help avoid a barn-like feeling and make areas more distinct.

One strategy Yip likes: In advance, "lay out your furniture as if you've already removed the wall, or sketch out a space-plan on a piece of paper so you actually know this is going to work for you."

"You want to make sure the rooms still function like you'll want them to function," he says.