As a builder I feel like I should know the answer to this, but would like to hear what the Tman experts think

Father in law has water coming down through a door jam. I get in the attic to inspect and its leaking from the dryer duct. Makes sense with the colder weather, its condensing. The duct leaves the dryer, goes straight up through the ceiling, makes a 90 and heads horizontally about 25’ until it 90s and goes straight up through the roof. The water is obviously collecting in the horizontal. He wants to duct tape the seams and call it good. I dont think thats a good idea. I was thinking about pitching it back toward the dryer 1/4”-1/2” per foot. It is insulated, but only with the standard insulation sleeve wrap of fiberglass. Whats the move?

Can you make it easier on your self snd vent into the house while its cold? Unless they're doing lots of wash for some reason? This time year when running heat. Most places can use little extra moisture in house. Just a thought. Sounds like pretty long run to mess with to me.

Mac

Pitching back towards the drying could help if you make sure the duct connection direction will shed water in that direction. If not, take it apart and flip it end for end (to change which way the crimps go)

if you insulated the duct would it stay warm enough in the duct to not condense?

Are all the heating elements in the dryer working properly?

I have dealt with ducting of all kinds extensively, and you are spot-on. Condensation in the horizontal run is the culprit. I will assume with such a long run it is exhausting out the gable end. That is good. I will hope it is a 4" smooth aluminum duct, which is required in bath and dryer ducting. NO FLEX! Do not use "duct" tape. That is for bush planes only.
You must install ducting with all seams facing up. All joints must be taped using the shiny silver tape made for ducting. All ducts in attics and crawlspaces must be insulated. This helps reduce, (though doesn't eliminate entirely under certain climate extremes), the condensation you are experiencing. You can use the thin fiberglass rolls usually used for pipes, making sure you get at least 2 layers, 3 or more preferred, but I recommend using batts. If you can cover the duct with R-11 or 13, that works well. If not, pulling the bats apart will at least give you better performance than the plumbing insulation.

The duct is smooth rigid. Not sure of the seem orientation as I haven’t dove into the fix yet. The duct is insulated but only with the standard fiberglass. It vents through the roof. After the long horizontal run it 90s plumb up. The long horizontal run is where the moisture is collecting. It seems like a bear to insulate it more and Im down to do it but I do t think that will totally alleviate the problem. I feel like pitching the duct back toward the dryer would be good as well. Ultimately, would that be harmful.

Do people vent dryer duct inside? That seems like a horrible idea?!

Sloping it won’t hurt, but the condensation is happening due to leakage. Seal it up & you’ll be good.

Ahh. Like leakage from poor taping? That makes sense

Sounds like a really long run. 25 feet of run in the cold space (assuming the attic is cold here). Maximum run for a dryer vent is supposed to be something like 30', with reductions for every bend. But, of course, if that's how it has to be run, then you gotta work with what you've got.

Besides taping the seams, consider insulating the pipe to keep the hot air hot, so the water won't condense to begin with.

Who in the world would design, and/or place a dryer that far away from exterior venting?

I dont know. Hvac isnt my specialty and these are real deal spec homes in this particular neighborhood

Atleast they didnt vent it inside.

When we moved into our current house the dryer was vented into the attached unheated garage. It would put steam and lint out there, a mess to get cleaned up and it condenced on the metal roof and dripped water on everything. I vented it outside ASAP.

Exactly, Id remodel and have the dryer next to the outside wall...we did that and have a 12" vent now.

I think it's the horizontal run, my guess

Hate to say it, but I would strongly suggest shortening the horizontal to 2' or so, (between the nearest top cord of the nearest trusses), and relocate the hood. Then patch the roof. That is what I would do if it were my roof, or if I was contracted to fix the problem.

I think you need to shorten the pipe to prevent the air from cooling and fostering condensation.

Would an inline booster can help? How about a catch basin to drain the water into, then duct it to the outside.

I’m an hvac guy. You’re absolutely on the right path. Sloping won’t hurt a thing but biggest thing is sealing everything. Every elbow is 7’ or pipe. The least amount of pipe the better, however air leakage (humidity mixing with a very dry discharge air) will cause condensation. Remove the ability for it to mix, and problem should be solved.

He is not wrong, shortening the pipe is better for everyone. But it can be a b***ch.