Preparing to Install a New Roof

Daily temperatures on a roof or in an unventilated attic can swing from 50°F to 150°F, thereby caus­ing tremendous expansion and contraction of roof materials. Improving ventilation under the roof, as shown in "Roof Venting,” on p. 76, can prolong shingle life somewhat, but the key to a long-lasting roof is the quality of the materials.

In the long haul, shingles with a 30-year war­ranty are a smarter buy than 20-year shingles because they last significantly longer, even though they cost only a little more. And most of a job’s cost is the labor.

WHEN IT’S TIME TO TEAR OFF

Short-term, you can save money by installing a new roof over an old one if local codes allow. However, new roofing applied over old (see p. 83) rarely lasts as long as roofing installed on a stripped and properly prepared substrate.

You must tear off existing roofing under the conditions at right:

Roof Longevity

If you observe product defects such as pre­mature wear or curling, ask the company that installed the shingles to inspect them and advise you on warranty issues. (Always keep records of installations.) If the company is reputable, it probably has a longstanding rela­tionship with the manufacturer and can exert more pressure to settle disputes than you could. If you don’t know or can’t find the installation company, hire another licensed roofing contrac­tor to inspect the roof and, if possible, identify the shingle type and manufacturer. If that con­tractor concurs that the shingles are defective— rather than installed incorrectly—contact an attorney who specializes in building-related claims to explore your options.

The roof already has two roofing layers. Two

is the limit for most local codes, because it’s vir­tually impossible to install a third layer that will lie flat. Even if you could, three layers would be a nightmare to flash and nail correctly. Underlying shingle layers are a springy substrate to nail through, and old wood shingles often split and migrate. Besides, if the bottom layer is wood shingles over skip-sheathing (1-in. boards with spaces between), only half of the new roofing nails would be likely to hit sheathing. Conse­quently, additional layers would be poorly attached and therefore wouldn’t last.

Sheathing and rafters show extensive water damage. When you can’t determine exactly what’s been causing leaks, it’s time to strip. The previous roofers may have installed flashing incorrectly or not at all. Or reroofers may have left tired old flashing in place. Whatever the cause, if the remedy is stripping back extensive sections of roofing in order to replace faulty flash­ing, reroofing may be the most cost-effective cure.

Rafters and sheathing are undersize. If rafters are too skimpy, the roof will sag, especially along the ridge. If the sheathing is too thin, the roof will sag between rafters and look wavy. In either case, consult a structural engineer. The remedy may be stripping the roof and nailing h-in. ply­wood over old sheathing or bolstering undersize rafters with new lumber; but let a professional make the call.

Shingles are prematurely worn, curling, or missing. If a roof is relatively new and these symptoms are widespread, suspect product

defects, inadequate ventilation, faulty installa­tion, or a combination of those factors. A layer of new shingles won’t lie flat over curling ones. So if shingles are curling—even if there is only a single layer of roofing—tear them off.

Adjacent roof sections must be replaced. This is a judgment call. When a house has additions that were roofed at different times, their need for replacement rarely coincides with that of the older roof—one section always has a few extra years left. Likewise, south-facing roof sections age 20 percent to 30 percent faster than north­facing ones. If you see signs of leaks, strip the whole roof, install flashing, and reroof.