It is the little things that make owning an old house difficult.

Most owners of old houses can handle the big items -- heating systems, walls, floors, roofs -- with ease. It is the decorative items, such as lighting fixtures, door knobs, security grills for doors and windows, that consume valuable weekend hours.

You have to choose appropriate style, pattern, or design or find a modern equivalent; find out how to maintain and repair the element, and, most difficult, find someone who sells or repairs the item.

Susan and Michael Southworth have written a book about one decorative and practical element that should help lighten the owner's workload. Ornamental Ironwork, which is $20, published by David R. Godine, Boston, with photographs by Charles C. Withers, is a beautifully illustrated guide to the history and use of the material in American architecture. It is also a very practical builder's guide and designer's manual.

The Southworths are evidently concerned that the reader have an appreciation for the material and the way it has been used in the past. They document ironwork development and show examples of its use in Charleston, Savannah, and New Orleans -- southern cities that were showcases of ironwork used for door grilles, window guards, balconies, verandas, fences, planters, urns, and garden furniture.

But they are also interested in good contemporary design, particularly the work of Samuel Yellin and Alvin Paley. Yellin, made the gates for the Children's Chapel at the Washington National Cathedral. Paley designed the forged and fabricated steel, copper, and brass gates for the museum shop at the Renwick Gallery.

The owner of an old house will be interested in the Southworths' suggestions on the practical domestic uses of cast or wrought iron work.

They are also concerned that window grilles, the ubiquitous burglar bars, add to the design of the window. The bars should be placed so that they relate to the muntins (the wood dividers that separate the panes of glass). They should not cut the panes in half. One guide in selecting the decorative elements for the bars is that they should complement the view from both the inside and the outside. The book also has suggestions on how to deal with other realities of urban living, fire escapes and air conditioners.

Aware that much contemporary ironwork is purchased to provide security, the Southworts have included a section on design considerations for defense. They say the upright bars in window or door grilles should be no more than 6 inches apart, that the lock area be especially protected, and that any grill be firmly attached if it is to be effective.

The authors find paint to be the most practical means of maintaining decorative ironwork. It should have a rust resistant base coat and a finish coat of flat oil-based paint, not highgloss enamel or latex.