Dryer vent

Should the dryer vent that passes through an attic be insulated in an unconditioned space? Can you see the condensation line in the insulation?


Yes, exactly for the reason you stated.

No need to insulate a dryer vent.

Is that penetrating the roof surface? If so, the shingles must be full of lint.

I like to see these penetrating the soffit area.


The dryer vent is on the roof. I think the other problem is not enough attic ventilation. The only vents noted where roof vents, no gable or soffit vents.

Funny, I would write that one up as improper if I saw it used as dryer vent. Improper vent material (supposed to be smooth, not corrugated) and the termination should not have a screen. Also the vent material looks like it would require inside / out assembly (i.e., downstream piece inside rather than outside the upstream piece).

“M1502.2 Duct termination. Exhaust ducts shall terminate on
the outside of the building. Exhaust duct terminations shall be
in accordance with the dryer manufacturer’s installation
instructions. Exhaust ducts shall terminate not less than 3 feet
(914 mm) in any direction from openings into buildings.
Exhaust duct terminations shall be equipped with a backdraft
damper. Screens shall not be installed at the duct termination.

So would I. I see that accordion-type junk all the time, plastic and foil, when looking at the outside vent it’s always packed full of lent just waiting to burn. Screens add more problems.

Overheated Clothes Dryers Can Cause Fires

When a dryer vent terminates on the roof… I’ve rarely seen the required damper/backdraft protection installed.

And that is exactly the problem!

Condensation can only occur when BTUs are removed to a point where a change of state from water vapor to liquid can occur. This will not occur when the dryer is pumping out hot air, or if stack affect (hot air rising up the pipe) is occurring in most cases. You must lower the temperature of the pipe not raise it for condensation to occur.

I would venture to say that there is a negative pressure in the house and cold air from the outdoors is being back drafted down the pipe cooling it off and the improperly ventilated attic space has sufficient water vapor to cause considerable condensation.

Remember, Buck is in Kansas. Hot summers and cold winters. Betcha the condensation problem only occurs in the winter. Thus the reason to insulate the vent pipe passing through the unconditioned attic space.

Thanks! for all the information.

We have many freezing winters here in Massachusetts and insulating a vertical dryer vent (that is penetrating through the roof) is not helping matters any.

As I stated above…the vent needs to be re-directed towards the soffit area under the existing insulation.