How do you, as a homeowner, translate these various approaches into action? I recommend you begin by establishing what you won't be changing. The following should probably be on your preservation list.
1) The Floor Plan. In older houses, the flow between the principal living spaces is usually quite logical. The interrelationship between the main entrance, the parlor, the kitchen, and the secondary entrance typically is practical and workable. In some homes, later additions changed the patterns of use (often confusing rather than clarifying things). If possible, retain the floor plan at least in the original portion of the house. In some cases, that may even mean restoring elements removed by previous remodelers. For example, in the early seventies, no one wanted a dining room, so the trend was to open them up to adjoining food preparation areas in order to create “country kitchens” or other multiple-use spaces in an open plan. Today the dining room is back. At first, an older floor plan may not seem flexible enough to allow for your planned renovations and a wholesale rearrangement may seem necessary. Try looking again.
2) Staircases. As the cost of quality craftsmanship has soared, the quality and character of the typical staircase have plummeted. If your stairway(s) have original balusters, rails, and newel posts, restore them. Strip them if they're of hardwoods or so coated with paint that turnings, panels, or other details are no longer crisp. Find ways to stabilize them (if necessary) that don't detract from their appearance. Badly worn treads can usually be replaced without too much difficulty, but be sure the details are restored, too, such as the nosing returns (that's where the rounded edge continues around the open end of the tread) New balusters to replace broken or missing ones can be milled surprisingly inexpensively if you shop around. Staircases are key design elements in a house, and well worth extra dollars to conserve and restore them.
3) Woodwork. Up until the years after World War II, moldings remained important design elements even in unassuming houses. Baseboards and casings around the windows and doors were made of wide stock, often with applied moldings to add shadow lines and a bolder, three-dimensional effect. Particularly in the late nineteenth century, cornices were heavy and dramatic. Save all that you can of the original woodwork, including any early paneling, built-in casework, spindle work, and other decorative wood treatments. Think of such wooden elements as worthy of restoration, but also as a source of inspiration. If your plan involves new elements such as windows, doors, or cabinets, try to replicate existing details. Using existing quality work as a source for new detailing will help give the new space a feeling that it is of-a-piece with the existing house.
4) Plaster Surfaces. Save original plaster where possible. New drywall lacks the strength, durability, soundproofing, and character of traditional plaster. Many techniques have been developed to preserve old plaster walls and ceilings, including special plaster washers that can reattach and stabilize loose and cracking plaster. When an existing partition is to remain in place, try to retain its plaster surface.
5) Floors. The history of change in a house is often to be read most easily in its floors. One with wide, hand-planed pine boards upstairs and machine-planed oak strip flooring down has been visited by remodelers, probably in the last few decades. A series of joints that form a line across the floor in the middle of a room for no apparent reason can indicate the shifting of a partition or the removal of a chimney. Unless your floors are both uniform and consistent with the style and vintage of your home, they probably can tell you something about the house. When you select flooring for new work, whether it's to be an addition to the house or a remodeling of existing space, consider how the new surfaces will suit surviving older flooring. Should you consider trying to find salvaged materials that will make the transition from the old to the new seamless? Do you wish to resurface much of the old flooring to match the new? Is there something in an original wood floor you can echo without copying its every detail - perhaps a border design, the board width, or the species and color of the wood? Or do you want to use an entirely different surface, like wall-to-wall carpeting in a new family room or tile in the new kitchen that coordinates with the old while not copying it? There's no one answer but ask yourself the question: Will the new suit the old?
6) Windows. If your home is a century or more old and its windows are original, the best approach almost always is to conserve rather than replace them. New weatherstripping can be added quite inexpensively, as can storms (sometimes on the inside, especially on historic houses). Old glazing compound can be repaired and even rotted elements can be replaced or the wood stabilized with epoxy or other consolidants. On newer houses, good copies of the original windows may well be available inexpensively. Whether you choose to replace or restore, do try to retain the original configuration. A homeowner who replaces the original multilight windows with single-pane sash (substituting, say, 1/1s for 6/6s) will change the appearance of a house, rather in the way that a pencil drawing is transformed when someone erases some of the shading. It's probably a bad idea.
7) Doors. As with windows and other details, try to save original doors. Doors removed in one part of the house can be recycled elsewhere. Find similar style doors at architectural salvage - they don't have to be identical, but if they resemble the originals, they won't seem out of place. The hold-on-to-the-original notion applies to exterior doors, too. Replacing a paneled front door that shows the wear and tear of many years may seem like just the right thing to do to save energy and tighten up the house. Yet many replacement doors today - sometimes of steel, often with faux graining stamped into the sheet metal - look like the architectural equivalent of a black eye. Think first about restoring the original door or, at least, finding a replacement in the same spirit as the original.
8) Hardware. Most vintage houses have been altered over the years and, typically, hardware is among the first elements to be changed. Hardware can wear out or break. Changing tastes may make a different style of doorknob desirable. Added security may call for updated locks. As a result, many houses have a range of hardware. Past remodelers may also have skimped on hardware. In new construction, most contractors specify inexpensive hinges and lock sets - and they look cheap, too, as the plating scrapes off. Often the quality of hardware changes from the public sections of the house to the private - expensive mortise locks in a high-style Victorian house often give way to simple latches in upstairs bedrooms. Know what your house has for hardware. Make sure you recognize the evolution of locks, latches, hinges, door knockers and bells, hooks, and the rest. Hardware is too often overlooked, both as a source of style ideas and for the clues it can offer about how the house was changed over time. A simple latch from an upstairs cupboard can prove to be the inspiration for the closure on the cabinets in your new kitchen or, when removed from a door, may reveal unpainted wood beneath, indicating it is original.
Other Original Elements: Not Necessarily Intended for the Public Eye. The skeleton of the house - its wooden frame, usually visible in the cellar and attic - may also give you some ideas. Solid old beams have been revealed in many old houses, though they often look like what they are: rough structural elements that the builders never for a moment intended visitors to see. Old masonry is to be regarded with the same wary eye: always conserve what you can, but don't be tempted to reveal surfaces if you believe that was never the mason's intention. Sloppy, untooled mortar joints and broken brick pieces that are just packed at random into openings are signs of masonry work that was to be covered up, perhaps by plaster or other surfaces.