A crack is not a diagnosis. What follows is the failure list by material, with the mechanism behind each one, because the mechanism is what decides whether the answer is a plank, an elevation or a re-side.
Vinyl: waviness, cracking and a distorted face
Waviness and oil canning. A run of panels that reads as a shallow wave in raking light has almost never failed on its own. It has been pinned: fasteners driven tight, fasteners off-centre in the slot, or a panel end sealed into a receiver. The panel grew on a hot afternoon, could not move, and went out of plane. It does not relax back.
Cracking and impact damage. Vinyl is brittle when cold. A ladder foot, a stone off a mower or a hailstone that would only dent a metal panel in July will crack the same vinyl panel in January. Cracks that start at a fastener slot are pointing at over-driven or off-centre nailing rather than at the impact.
Chalking and fade. A powdery residue that comes off on your hand is the surface of the capstock breaking down under ultraviolet. It is cosmetic until it is uneven, and the elevations tell the story: south and west go first.
Distortion from reflected sunlight. A melted or wavy patch in an oddly local area, often facing a neighbouring window, is a reflection problem rather than a siding problem. Concentrated reflected sunlight off a low-emissivity unit can exceed what the panel tolerates. Replacing the panel with the same product in the same place repeats the result.
Panels that have unzipped along the bottom lock, or gone loose at a corner after a wind event, are pointing at hem engagement and fastener spacing at the edges.
Fiber cement: chalking, over-driven fasteners and wicking at the cut edge
Chalking. A cement-based board handing you a fine powder is losing its surface coating. On a painted board that means the coating has reached the end of its useful life on that elevation. It is a repaint decision, not usually a replacement one.
Cracks radiating from fastener heads. That is an over-driven fastener. The head crushed the board when it was set and the crack opened later. It is an install signature, and if it is visible on one board it is usually on a great many.
Open butt joints and failed sealant at joints. The question is not the gap, it is what sits behind it. Where joint flashing was installed, an open joint is cosmetic. Where sealant was the only defence, water has been running down the sheathing.
Swollen, soft or delaminating bottom edges. Two causes, and both are detailing: an unsealed cut end, or insufficient clearance to grade, to a roof or to a deck. A cement composite in contact with standing water wicks, and the bottom course goes first.
Efflorescence. A white bloom is salts moving out of the material with water. The bloom is the symptom; the water is the finding.
Engineered wood and hardboard: it fails from the bottom edge up
Swelling and mushrooming at the bottom edge of a plank, then delamination in layers, is the classic hardboard sequence, and it catches poorly detailed engineered wood as well. The face can look sound while the edge has already gone.
Paint peeling within a season or two of a fresh coat is usually failing from behind: moisture in the substrate pushing the film off. Repainting over that buys a season.
Press a screwdriver into a suspect edge under a gutter, a window sill or the bottom course. If it goes in, the board is finished at that point, and the only remaining question is how far the damage runs.
Wood: cupping, checking and end-grain rot
Cupping is a board wetting or drying faster on one face than the other. Flat-sawn boards cup away from the heart, and a board that was never back-primed cups first and cups worst.
Checking is surface splitting along the grain from repeated wet-and-dry cycling, which is exactly what a dry climate with a wide daily swing produces.
Rot starts at end grain and at joints, not in the middle of a board. Look at butt ends, at the bottoms of trim legs and at the junction between trim and cladding.
Metal, stucco and the fastener you can see
Metal siding chalks much as vinyl does, dents rather than cracks, and corrodes where two dissimilar metals meet in the presence of water. A mismatched fastener in an aluminium panel is a small battery.
Stucco cracks tell you where the movement is. The ones worth acting on are the ones that hold water, and staining below a window in a stucco wall is usually a flashing finding rather than a stucco finding.
Rust streaks below fastener heads, on any material, are a fastener-class problem: the wrong corrosion class went in. The stain is cosmetic and the message is not, because it says the fastener specification was not followed, and that is rarely the only thing that was not followed.
What tells you the problem is behind the cladding
- Staining, blistering or peeling that appears as vertical streaks below one specific point
- A musty smell at an interior wall, or a soft spot in drywall at an exterior corner
- A roof edge dying into a wall with no kickout flashing above the damage
- Damage concentrated under a window rather than spread across an elevation
- Insect activity, which follows softened wood rather than causing it
Damage in a pattern points at a detail. Damage everywhere points at age.
Repair, section replace, or re-side
Repair a panel or a plank when the failure is local, the cause is known and the cause has been removed. A cracked board under a gutter that now drains somewhere else is a repair.
Replace a section when a whole elevation shares one mechanism (the sun-facing wall, or the bottom two courses the whole way round) and the rest of the house is sound.
Re-side when failures show on several elevations at once, when the substrate is wet, when the material is out of production so nothing will match, or when the drainage plane behind the cladding has to be rebuilt. That last one is the real trigger, and it stays invisible until something comes off the wall.
Which is why anything we quote as a repair gets quoted after we have taken something off and looked behind it, rather than from a photograph.
