Fix Now, Save (A Lot) Later

Potential problem: A storm could send large branches crashing down on the roof, and wet leaves against the siding can cause algae to grow, leading to rot. "These branches also act as a superhighway for any kind of varmint wanting to enter your house: squirrels, raccoons, and even rats," says Roger Cook.

Fix it now: Trim a small tree yourself using a pole saw, taking care to leave the branch collar to prevent disease. For bigger jobs hire a professional arborist, who'll typically quote you a flat rate—figure $75 to $95 an hour, depending on the height of the tree and the number of branches involved. To remove algae from siding, power-wash with a solution of 1 part nontoxic oxygen bleach to 10 parts water; power washers rent for $50 to $75 a day.

What you'll save: From $50 (for asphalt) to $395 (for slate) per 10-by-10-foot square of replacement roof shingles, plus $150 an hour for labor. Expect to pay $800 to $1,250 to replace 150 square feet of rotted yellow pine, spruce, or fir clapboards, including labor. And to trap those pesky rodents, tack on $300 more.

DIY: See Roger Cook's fall yard-work checklist.