If you think roof leaks are only a problem if you live in a climate with frequent rain, think again. While roofing problems are obviously most often caused or exacerbated by rain, there are other lesser-known sources that contribute to roof leak issues. Whether you’ve got a new home or an older one, most roof shingles, on average, can go 15 years without needing repair. But a roof can get in bad shape well before the 15-year mark, and the longer you wait to repair it, the more expensive the repair will likely be.

To keep repair costs as minimal as possible, be aware of some problems that can cause serious roof leaks, and stop them at the source whenever possible. A home inspector should check for all of the following problems:

1. Incorrect shingle installation. Don’t rely on looks alone; even the strongest shingles won’t stand up to rain if they’re not properly installed. Improper joint locations and a lack of underlay are two issues that are particularly hard to see, but can be extremely problematic.
2. Structural sagging. A sagging roof structure is often the result of moisture retention, and nearly always foreshadows, or coincides with, a leak issue.
3. Water “ponding.” Clogged roof drains and indented areas on flat roofs can cause water pooling.
4. Damaged nails. Even on shingles that have been expertly installed, nails are the first thing to show wear. Corroding nails leave microscopic holes that invite water in.
5. Improperly hung gutters. Gutter placement is critical, and if you’re in an area with strong wind, just a tiny shift can tamper with the gutter system and divert rain onto the roof.
6. Moss. You might think it’s just an aesthetic problem, but as moss gathers, it retains more and more moisture that you might not be able to see—until it starts dripping into the attic.
7. Insufficient insulation. The roof might look great on the outside, but if it’s not properly insulated underneath, you’re in trouble. Pre-1980s homes, in particular, may not have an adequate vapor barrier; if they don’t, a replacement is warranted.
8. A deteriorating chimney. Whether its cracks, eroded joints or a decaying cap, the chimney has plenty of inroads for moisture and water. Don’t discount the chimney; sometimes it might need all the repairs, when the roof might be just fine.
9. Evidence of badly-done past repairs. From improper plastering to inadequately plugged-up holes, any past repairs that look like they’re DIY are probably not up to code, and are just a stopgap measure. Have a professional inspector evaluate these fixes, and suggest ways to re-do them properly.
10. Don’t forget the attic. Leaks into the attic aren’t just a problem; but so are leaks originating in the attic.