Siding usually fails slowly, then all at once. The early signs are easy to miss or wave off, but on a Bellingham home in our wet climate, the longer you wait, the more likely it is that water has moved from the siding into the sheathing and framing behind it. Here are seven signs your siding is failing, what each one means, and when it's time to call someone.
1. Soft spots you can push into.
This is the big one. If you can push a screwdriver or even a thumb into the siding or the trim and it gives, the material is rotted and water has been sitting there. On homes with old hardboard or T1-11, soft spots at the bottom courses and around windows almost always mean the sheathing behind is wet too. This is not a cosmetic problem, it's a structural one starting.
2. Bubbling, swelling, or delaminating.
Hardboard and T1-11 swell and bubble as they soak up water, and the layers start to separate. Once that starts it doesn't reverse. Swollen edges and a wavy, lumpy look mean the material has failed and is wicking moisture into the wall behind it.
3. Water marks on interior walls.
A brown water mark on an inside wall or ceiling, especially below a window or where a wall meets the roof, is water that got past the siding and the flashing. By the time it shows up inside, it's been getting in for a while. This is the sign that most often turns a repair into a bigger job, because the water has had time to work.
4. Gaps, cracks, and missing pieces.
Cracked boards, gaps at the seams, and pieces that have fallen off or pulled loose are open doors for water. Even small gaps at the corners or around windows let wind-driven rain in. In our climate, an open seam is a slow leak.
5. A finish that won't stay, no matter what.
If a wall has been refinished more than once and the finish keeps peeling, the problem usually isn't the finish itself. It's moisture coming through the siding from behind, pushing the finish off. Chronic peeling in the same spot is a sign the siding or the flashing is letting water in.
6. Moss, mildew, and dark streaks.
Green moss and dark mildew streaks, especially on shaded north walls, mean the wall stays wet. On their own they're a maintenance issue, but combined with old hardboard or cedar that can't dry, they're often the visible top of rot that's started below. Cornwall Park and Silver Beach homes see a lot of this.
7. Rising energy bills and drafts.
Failing siding and a compromised weather barrier let air move through the wall, which you feel as drafts and see on the heating bill. It's a softer sign than the others, but paired with any of the above, it points to a wall that's no longer doing its job.
By the time siding shows it's failing on the outside, the question isn't whether to act. It's how much of the wall behind it is already wet.
Repair or re-side?
One bad wall or a few soft boards is often a repair. We open the affected area, fix the water path, and replace the damaged sheathing and siding, which we cover in our guide to the rot we find behind old siding. But if you're seeing several of these signs across the house, or the siding is original hardboard or T1-11 from the 70s through 90s, a full re-side is usually the better spend, because patching failing material just delays the inevitable. The siding cost guide can help you weigh it.
For a free walkthrough and an honest call on repair versus re-side, Bellingham Siding Co. handles siding and rot repair and full re-sides across Bellingham and Whatcom County.