Leaking shed siding.

[CathyA]

I wasn't sure where to post this. Its about my chicken coop, but yet it could apply to a regular shed. We had this shed built over 8 years ago. The guy that built it did a horrible job, and we've had to make repairs on it ourselves.
Its one of those sheds where they use panels of wood that connect together.

Anyhow.........the side of the shed is leaking badly and has been for several years. We thought it was a poorly-installed-window-caused leak, but now we're realizing that its leaking where the pre-fab shed panels come together. What's weird is, there's absolutely no sign of a break in the paint or the panels on the outside. When we use a hose on those seams though, it leaks. Very strange.
We'll probably end up just caulking in that little channel from top to bottom where 2 pieces of siding are put together, on the outside, .
Any construction people out there have any ideas why these vertical seems would be leaking rain, when they look perfectly intact on the outside?
Thanks.

[sweetana3]

Boards shrink and expand with humidity. Board and batten siding helps with this. If your panels are vertical, consider applying a batten or thin piece of lumber over the seam and caulk. This piece can then shrink or expand and it will still cover the seam.

[Marianne]

I hate leaks. That water can really travel before it becomes visible. I'd also check higher up right after a rain (or the garden hose) using a flashlight.

[goldensmom]

It sounds like the siding you are describing is exterior composite lap siding. We have a 14 yr. old shed with the same siding and have never experienced leakage from the seams but the weathered composite layers are separating (even thought it has been treated) and we are going to reside the shed with metal barn siding. If I had the problem you describe I probably would caulk the seams and see if that fixes it. If it still leaks and as water travels, do as Marianne suggested look further up for the leak.

[CathyA]

Thanks everyone,
Sweetana, I've looked up the batten fix, and it looks promising! I wonder if we could just try caulking that seam first? I suppose using battens would be even better.
The guy who built it did a really bad job. The roof has been leaking in several places too. We're not very mechanical with things like leaky roofs, so we'll probably need to call someone for that. But money is really tight, so it might have to wait. Its "just" my chicken coop. If it were the house roof leaking, we'd have it fixed immediately. But I still want it to last a long time.
I wish we had a construction person in the family!
I had a ridge vent put in the top for ventilation, which I wish I hadn't. I don't think he put that in right either. And he didn't put the windows in right, nor the door. I had to pay someone else to come back and fix everything. :(
Thanks so much for your suggestions!