Finding shingles to match is not a problem when Waller Construction, Lakeland, Fla., is building an addition. If the existing structure is roofed in asphalt shingles -- and most are -- matching product is a cinch. It's whether or not the existing roof should stay that is the issue.

"If they're putting on an addition," says vice president Jimmy Waller, "it means they've been there for a while." Or, at least, the house has. Many of the homes the company works on are 40 or 50 years old.

Waller estimates that in three out of four additions, a new roof is an appropriate suggestion. He brings it up at preconstruction meetings by asking clients if they've thought about the existing roof and what the house will look like without a new one. "We give them the choice of tying it in, as it is, by redoing the existing slope from the ridge down at the tie-in point, or of going ahead with a roof inspection."

The inspection takes 30 minutes. An employee diagrams the roof, looks at suspect areas, checks valleys and flashing, and walks the roof to see if roof decking is soft anywhere. The client is left with a written analysis. If they decide to replace it, that's a separate proposal.

Economies of scale

On addition jobs, Gardner/Fox, a design/build company in Bryn Mawr, Pa., assesses the roof, describes the pros and cons of replacement, and lets clients decide. But if the roof has less than five years left in it, says secretary-treasurer Mark Pennington, "we strongly suggest they make the change, because of the economies of scale in doing it all in one shot."

Customers might object that a new roof is not in their budget, that the existing roof looks fine, or that they don't care that much about matching new and existing anyway.

Typically, two arguments convince customers that a roof with a limited life span should be replaced: They won't have to worry about leaks into the foreseeable future, and the uniform look of the existing structure and the addition is more attractive.

But function usually prevails over form. Tacking a new roof on usually runs an additional 5% to 10% of total cost at Gardner/Fox, where additions cost anywhere from $100,000 to $250,000. "They won't go to the expense of replacing a good roof just for aesthetics," Pennington says.