Commercial conversions are harder than they look.

The lack of New York City housing is turning many developers to convert former loft and office buildings into new apartments. From the Upper East Side's Richmond, created from an old storage facility by developer Ian Bruce Eichner, to the luxurious Trump International Hotel & Tower, transformed from the former Gulf & Western Building, to Downtown's numerous conversion jobs, architects and developers are working within the old four walls to create designs for living.

Changes are often complex to implement but predictable in their needs: new plumbing, gas for kitchens, individualized climate controls and operable thermopane windows. But others, like a building in the wrong zoning district, Americans with Disabilities Act compliance (ADA), or main features like an elevator or staircase or even an entire core that need altering, can come as a financial surprise.

The problems, the professionals say, come when not enough due diligence is done before the buyer makes the purchase and the hidden costs aren't revealed until it's too late.

In today's quick-moving market, turnaround time on decisions is sometimes key to making the deal. But an uninformed decision can be a costly one, because even a seemingly no-brainer conversion can turn into a no-profit one when the architect or marketing consultant gives you a reality check.

"Do a careful feasibility study and do not buy based on square footage," warned noted architect Costas Kondylis, who has conversions from Trump International Hotel & Tower to The Exchange at 25 Broad Street to his credit, as well as many new buildings.

Says loft conversion architect Joseph Pell Lombardi, who gets calls from several clients whenever a building comes on the market, "Even a fairly sophisticated developer will come to me and say, 'It's going to be the easiest conversion. We just have to finish out the apartments.' Wrong. They figure it would be a $40 conversion and it's a fullblown $100 conversion."

Lombardi immediately checks land maps - which show core locations, lot line windows, zoning location and other data, to get as 'much information as possible for his clients right away. "A day later I can get floor plans from the Dept. of Buildings," he added.

His office computer also contains pro formas for different kinds of building conversions and helps figure out the development costs and income projections needed for a lender.

While Lombardi can do a quick turnaround to see if the building will be a quick and easy or long and costly conversion, for some projects, months can be needed to do the right job.

The need to conduct extensive due diligence was stressed by Scott Coopchik, executive managing director for Galbreath, who is overseeing the Trump International Hotel and Tower (TIHT) changeover to luxury residential use after its past life as the Gulf & Western/Paramount office building.

Carefully define what you are going to be doing to identify the costs, Coopchik said. "Decide what systems you can use and those you cannot," he emphasized. "Know the zoning laws that will affect it in the change of use."

At TIHT, residential marketing expert Louise Sunshine was brought in months before the Columbus Circle building was purchased. She did marketing studies to see what comparable buildings were getting price-wise and helped define what the potential buyers would want in the units.

"A lot of people will design and build," said Coopchik. "We had her on board first and she gave direction and input all the way, and the units were designed with the market in mind."

Be creative and clever in the re-use, continued Coopchik, who warns that while morphing from office to residential "the loss factors will change and the net rentable will change dramatically. If you do your homework you can do well, but you can't leave anything to chance. The surprise can cost you a lot of money."

Coopchik said they avoided surprises by knowing what they were getting into and what needed to be done to achieve their goals.

Most buildings changing from one use to residential have alterations that are destined by code, while others are dictated by market tastes.

Architects say residential buildings need two staircases to meet fire codes, while old elevators don't usually meet new ADA sizes.

Big apartments are desirable, but the developer doesn't always get the price he wants per square foot for larger units.

A mistake can be made when the developer does not factor in the cost of the solution when the core of the building is in the wrong location, a typical problem in commercial buildings originally developed to obtain easy street deliveries. But that same core can block the needed windows.

At Trump International, Coopchik said they purposefully shifted the core out of the portion of building facing Central Park, and that gave the developers more salvageable and highly desirable square footage.

If the building is too deep, i.e. too far from the core to the windows - more than 60 to 65 feet seems to be the consensus - the apartments also won't lay out well. Large beautiful apartments may be a selling point but will decrease the price you get per foot and merely create odd spaces.

Instead of having a 700 square-foot one-bedroom unit, it will layout to 850 square feet. "You will not be able to charge that much more rent for that extra square feet," said noted apartment architect Costas Kondylis. "For people on the market, a one-bedroom is a one-bedroom." He noted, however, that because the apartments are larger, they will become more desirable and people will get a bigger apartment for their money.

"While the per unit price is good, the per square foot price is lower than other segments in the Manhattan market because the apartments are big," said Welder, who has worked on conversions including the Printing House and the Victoria at Union Square.

"If you are trying to get $300 to $400 a foot, and giving the 1,200 square feet, there's an ultimate dollar price that's going to be paid for it. For the consumer, you are getting more space for the dollar; for the developer you are getting a product that works in a tight market."

At The Exchange, Bruce Menin's conversion of 25 Broad, Kondylis says they were able were able to create a foyer area near the entryways by using the extra space, which can double as a dining area or a home office.

And in his layouts for the luxurious Trump International Hotel and Tower, Kondylis says the additional territory enabled them to provide the "super luxury" clientele with his and her bathrooms and dressing rooms, not to mention larger bedrooms. With residents there paying an average of $1,000 a foot, Trump is one of the few converters who will not lose on the larger apartments.

Kondylis has consulted on projects where the buildings were wedding cake style, and while the base floors were just too big and deep for residential usage, the tower portions worked.

"We recommended commercial usage for the base and residential for the upper floors," he said.

When Donald Trump first purchased 40 Wall Street, he always knew the tower portion would be desirable for office space or for residential use, and that the base could only be used for commercial tenants.

What made him decide to keep the entire building a commercial office tower was the idea of changing over 3,000 brand new Wasau windows, "the most expensive and best windows," and two brand new York chillers that wouldn't work well for a residential adaption.

Sam Spata, senior principal of HOK PC architects, who is working on the office renovation at what is now dubbed The Trump Building, said because there were many private offices, labs and cafeterias throughout 40 Wall, there was piping available for a residential conversion.

'It could have worked for them [as residential]," he said. "But some of the pipes [coming off the risers] were old and some were put in for tenant fit-out, and those would have had to be changed."

Trump already had a law firm in place in mid-tower, but that also could have proved costly if he had converted the rest of the tower to residential use.

One bonus for converters, they think, is that they have the ability to leave a commercial tenant in place while they create apartments above, below and even on the same floor. Think again. "Let's say on the 20th floor there is a commercial tenant," said Lombardi. "Yes, you can have the tenant in place but you have to sprinkler the stairs that are common to both."

Kondylis says one benefit of older commercial buildings is that they were over-elevatored and the extra shafts can be closed off and the square footage recaptured for residential usage.

But obstacles for residential conversion can arise when staircases and elevators meet, as they do in some older buildings.

"Every once in a while we get someone whose bought a building with one stair opening into the elevator core," Lombardi said. "It's not good for residential. It's a major problem."

Architects will try to save existing stairways and as many elements as possible, or the conversion costs becomes prohibitive, stressed Kondylis.

He advises that the building shouldn't need a major renovation of the exterior, merely maintenance work like repainting, steam cleaning and almost always a window replacement.

Lot line windows, selling point view or not, also don't count towards residential code requirements for light and air.

"I've consulted for owners whose magnificent views are lot line windows," said Paula Wexler, president of Habitations and a consultant to converters. "If you are doing this for a condominium or a co-op, you have to disclose that that may not be there forever."

Of course, everything else has to be new on the inside. "We used to call them gut rehabs," Kondylis chuckled, ticking off the electrical, the plumbing, the bathrooms and kitchens, as needed new essential elements.

Many times, the problems come from the necessary new electrical, plumbing and airconditioning systems. "People don't want to buy something with a little bit of age. It has to be new," explains Lombardi. Recall that purchasers and their attorneys are going to be reading offering plans that must disclose this information.

"You can pay a premium for a building in good shape," said Lombardi. "But you would have been better off with a wreck of a building because you are going to have to replace it all."

Wexler says new codes require the whole building, in effect, to be in ADA compliance. "You run into problems in the smaller loft type office buildings because the elevators are too small," she said. "So some of them are not feasible [as conversions] or the cost would exceed the value."

Developers also need to be cautious about Landmark districts which might involve unanticipated costs when you want to add five or six floors.

And a small unit conversion on an otherwise commercial sidestreet can make potential residents nervous about security.

"From a consumer point of view, there is a level of hesitancy in terms of security and access," said Wexler.