Anyone who has stripped cladding off a house knows the pattern before they start. The wide open field of a wall, where there is nothing but panel over barrier over sheathing, is almost always in fine shape. Water hits it, runs down it, and leaves. There is nothing to interrupt that trip and nowhere for water to be handed from one surface to another, which means nothing to get wrong. A field of siding is a simple problem, and simple problems get solved by gravity.
The damage is at the interruptions. Every window, every door, every hose bib and dryer vent, every deck ledger, every place a roof edge meets a wall, and the whole bottom course where the wall has to drain. Those are the points where the drainage plane has to be cut, lapped, flashed, and reassembled, and every one of them depends on somebody getting the order right on a day years ago. That is where you should look, and that is where a contractor should look first.
An opening in a wall is a hole cut through the drainage plane. Making that hole watertight is a sequence: a sill pan or flashing at the bottom, the barrier lapped over the flanges at the sides, and head flashing over the top with the barrier lapped over that. Done in the right order, water that reaches the opening gets turned back out onto the face of the barrier and continues down. Done out of order, the same water goes behind and into the sheathing.
Which is why the most common thing found behind cladding is a window with no real flashing and a bead of sealant carrying the whole responsibility. Sealant is a consumable. Utah sun and dry air work on it hard, and once it opens, water has a direct path into the wall at the exact place the assembly is weakest. If you have interior staining under a window or trim that will not hold paint, this is the first place to look.
Deck ledgers are the worst offenders because they are big, they are structural, and they are attached through the cladding into framing. A ledger installed without flashing above it collects water in the joint between the deck and the house and delivers it straight into the rim joist and the sheathing. It is hidden by the deck itself, so it can run for a decade with nothing visible from the yard. By the time a ledger leak shows itself, the deck usually has to come off the wall before anybody can fix it properly.
Smaller penetrations do the same thing in miniature. Hose bibs, dryer vents, exhaust caps, satellite mounts, light fixtures, and the electrical run somebody added later are each a hole in the drainage plane. Handled well, they get a flashed or gasketed detail that keeps water on the outside of the barrier. Handled badly, they get a ring of caulk. Look at how many of them your house has and you get a sense of how many chances there were to do it wrong.
A wall gets rain. A wall at the bottom of a roof gets everything the roof collected. That is the difference that matters at wall-to-roof intersections, and it is why those junctions are so unforgiving. A lower roof that dies into a taller wall is the classic case: without a kickout at the end of the run, water coming down that roof edge goes behind the cladding instead of out into the gutter. All the water landing on that roof funnels through a few feet of edge, and that edge is often inches from your cladding.
The damage from that is distinctive because it is narrow and deep. A single wet column of sheathing running down inside a wall, sometimes reaching the foundation, with almost nothing visible outside until the wall gets soft or interior finishes start staining. Roof work itself is a separate trade and a separate job, but the flashing where that roof edge hands water off to your wall shows up on the wall side, and it gets found when cladding comes off.
The lowest run of siding lives the hardest life on the house. It takes splash off concrete and rock, it sits behind piled snow for weeks in a Wasatch Front winter, and on plenty of Utah homes it gets hit by sprinklers several times a week from April to October. It also has the job of letting the wall drain, since whatever comes down the back of the cladding has to exit at the bottom. That is a great many jobs for one run of boards to do at once.
So problems concentrate there. Swollen or rotted bottom boards, a buried starter course with soil or bark against it, a weep path packed with landscaping. Any of those turn the base of a wall into a place where water arrives and cannot leave. It is also the most fixable set of problems on this whole list, because most of it is about grade, drainage, and where you point a sprinkler head rather than about the cladding at all. None of it is exotic, and most of it is visible from the yard on a Saturday afternoon.
Sun is the constant here. High-altitude ultraviolet works on finishes and on sealant far faster than most people expect, so the caulk joint that looked fine three summers ago has often opened up. Dry air pulls moisture out of wood and makes it move seasonally. Neither of those puts water in a wall by itself, but both of them open the paths that let water in. What sun and dry air do is open joints, and open joints are exactly what water needs.
Then freeze-thaw takes over. Anything that has already opened up, a hairline crack, a lifted seam, a gap at a trim joint, will take on water and then have that water expand in it repeatedly through the winter. That is why so many exterior problems along the Wasatch Front look like they appeared suddenly in spring. They did not. They were opened by sun in the summer and widened by ice all winter, and spring is just when you finally saw them.
Yes, and that is the ordinary case rather than the exception. Cladding is the layer that sheds sun and rain, and it can be doing that job fine while a flashing detail behind it has been leaking for years. The signs are usually indirect and interior: recurring stains, soft spots, a smell, fasteners moving. Cladding that looks good is not evidence that the wall behind it is dry.
Windows and doors, then anything bolted through the wall, then any place a roof edge meets a wall. Those three account for most of what turns up when cladding comes off. Start where the interior evidence is, if there is any, and work outward and upward from there, because water enters above where it shows and travels down before it stops.
Sometimes, in the places sealant was designed for, and almost never as a substitute for flashing. A caulk joint is a consumable that Utah sun degrades, and it is the wrong tool for a detail that has to work for decades. Worse, sealing the outside of a wall that is already wet can slow drying, which is the opposite of what a wet assembly needs.
A minute of detail now saves an hour of guessing later, on both ends.
