It seems like a small change - and an obvious one - but it forced architect Robert Mainwaring to completely rethink his design of the new pavilion at Paoli Hospital.

Hospital leaders, who were converts to a new trend in health care called evidence-based design, wanted to see if they could prevent falls by making it easier for patients to walk to the bathroom.

Traditionally, patients have had to walk all the way across their rooms, often through a maze of equipment and furniture, to get to the toilet. Paoli wanted the bathroom on the "head wall" of the patient's bed, with a rail on the wall between the bed and the bathroom door.

Having that short, unobstructed and supported path "was the driver that reconfigured the room," said Mainwaring, vice president of Robert D. Lynn Associates in Philadelphia. The resulting asymmetrical design, which is also meant to reduce infections, improve communication with family members and maximize exposure to natural light, is an example of how hospital leaders are beginning to see their buildings not simply as spaces for housing the sick but as tools for fostering healing.

Paoli officially opens its new, $145 million, 124-bed pavilion July 27, although donors have already had a chance to savor that new-hospital smell. The ribbon cutting is later this month. The pavilion, which doubles the size of the Chester County hospital, is one of 50 Center for Health Design "pebble projects" in the country and the first in Pennsylvania. The "pebbles" - a reference to ripples from a pebble thrown in the water - agree to pursue and share research on the impact of design changes on patients and staff.

Two replacement hospitals now being built in New Jersey by Virtua Health and Princeton HealthCare System are also pebble projects and incorporate similar features.

Debra Levin, president and chief executive officer of the Center for Health Design in Concord, Calif., said interest in evidence-based design has increased in the last three years. "We still have a ways to go," she said. "It is by no means the commonplace way of doing things." Pebble hospitals pay her center $40,000 a year.

Barry Rabner, president and chief executive officer of the Princeton system, said it's high time hospitals were designed in a more scientific way. "It is remarkable to me that we have some 5,000 hospitals in the country and we are now just beginning the science of evaluating these features," he said.

"If we designed airplanes the same way we designed hospitals, we'd be in trouble."

At a time when just about everybody is thinking about saving money, a new project like Paoli's, with its large private rooms and attractive gardens for patients and families, can look awfully posh.

But hospital leaders say that, while upfront costs are higher, better design saves money in the long run by reducing complications and improving staff efficiency.

"If you look at cost over time and you really do reduce errors and you really do reduce infections and falls, you'll save a fortune," Rabner said.

Private rooms are required by law in new hospital buildings in Pennsylvania, and Rabner believes they soon will be in New Jersey. Not only do they reduce infections, but they give hospitals more flexibility because they don't have to worry about matching roommates by illness and sex.

Barbara Tachovsky, president of Paoli Hospital, said insurers were increasingly reluctant to pay for mistakes and preventable complications, problems she hoped the new design would reduce.

The most striking difference between Paoli's old and new rooms is the size. In the old rooms, beds for two patients are only about five feet apart and separated by curtains. It's not possible to have a private conversation, and all the equipment and furniture make it hard to maneuver. Nurse Helenann Meenan said she fell and broke her shoulder when she tripped over a chair in a room. One of her patients on a recent day, Candice Larsen, said switching to private rooms is "the best idea in the world."

The new private rooms are 225 square feet - 65 square feet bigger - and built at a slight angle for better visibility from the nurses' station and hall. The bathroom is indeed next to the bed and the railing is within fairly easy reach. Medical equipment will be placed on the other side of the bed so it won't be in the way.

The rooms have big windows. Natural light and views of nature have been shown to improve healing. Even paintings on display have been chosen with the idea of bringing nature inside.

Each room has a couch for visitors that folds into a bed. There's evidence that better communication with families also helps patients get better faster.

To prevent infection, there's a sink just inside every door to encourage caregivers to wash their hands.

All of the rooms are identical or "same handed," a design feature that experts believe will reduce confusion among nurses and doctors.

Contact staff writer Stacey Burling at 215-854-4944 or sburling@phillynews.com.