Dryer vent passing through the attic

I was at a house yesterday where I asked the seller why he was using a long flex hose running across the floor from his dryer to a vent on the side of his house and not just run a smooth wall steel duct up through the ceiling, across the attic and out the side of his gable roof wall. He said at one time he did, but when the city building inspector came to inspect his new water heater, the inspector pointed to the vertical duct and told him that was a code violation.
I called an inspector friend of mine and he said the flowing lint will loose energy and fall back down, creating a fire hazard. Made sense to me at the time.
I furthered researched IRC chapter 15, section M1502 and I see nothing against vertical rises.
So is running the dryer duct up to the attic and out the side of the house a code violation?

Thanks in advance for you help.

Louisville Home Inspections

It depends on how long the run and how many bends.

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Roy, it’s less than the 35 feet minus 10 feet for two 90 deg elbows. It’s about 8 feet up and 12 ft over.

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M1502.6 Duct length.

The maximum developed length of a clothes dryer exhaust duct shall not exceed 35 feet from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet for each 45-degree (0.8 rad) bend, and 5 feet for each 90-degree (1.6 rad) bend. The maximum length of the exhaust duct does not include the transition duct.


It is if the city building inspector says it is.

Normally I would agree, but he removed the vertical pipe and I don’t know what kind of pipe it was. He has 4" pvc in the attic which was not removed. So if the inspector was pointing to the pvc, than yes I see the problem.
So, speaking hypothetically, would smooth wall steel up and out be acceptable?

If it was WELL insulated and a relatively short run, I wouldn’t have a problem with it.

I had the exact thing…about a 6’ run up, and had zero problem with it here in northern MI. It didn’t condense and drip back down to the ceiling elbow.

However, I would prefer to run it horizontally, under the insulation and out the gable. :smile:

Manufacturer’s requirements can come into play too.

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If you can’t run dryer exhaust vertical, then how would you deal with a dryer in the basement. I’m sure that’s not a unicorn.

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I agree but I’ve never seen a dryer vent “‘installed” in a basement. All I’ve every seen were homeowner installed.
And I’m impressed how quickly you thought of that, it told me a couple days to think of that.

Just wondering, since when did home inspectors become “Code” inspectors.
Who really cares?

As for dryer vents in a basement …. I saw them every day! We have lots of basement laundry rooms in my neck of the woods.

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My dryer is running right now.
The vertical vent terminates thru a roof vent. :cowboy_hat_face:

It’s not about code it’s about safety. I would think going up 5ft is different than 9 ft too.

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Very few flex ducts will meet the intent of the IRC. The duct ribs will cause problems.


Gary, I guess you would have to ask the inspector

We have almost no basements here and 99% of the inspections we do the dryer vent goes up through the roof.

That’s good to know. Thanks

I see them vertical through the wall and attic all the time. What I see now is this sticker on the vent wall box detailing the vent equivalent distance. I let the client know that it is very important their dryer is rated for that distance.

You better chase it down Marc. :drum:

Here’s one from yesterday. They just kinda tried to direct the exhaust near a soffit vent. :open_mouth: