Bath fan:PVC ductwork?

[Juan for the road]

I am installing a new bath fan on a remodel.I want to use 4" PVC pipe for the ductwork for a 16' run and out the soffit,with a 90 degree elbow facing down with a grate and insect screen.I will also install an inline flap/damper just inside before it gets to the soffit(in addition to the flapper in the fan itself).

Yes,there is attic space above,however this area will be finished space in the future,I need to keep it clear and free of ductwork.

Is there any kind of code issue here,as far as type of ductwork used?I'm planning to use 2 feet of metallic dryer vent immediately out of the fan,then transition to the PVC,to allow for some flex to be able to change the fan in the future and for some fire protection,should the fan motor ever burn up.

[hj]

None that I know of, because it is not a health, structure, or sanitation issue.

[Chris75]

Why even struggle with the pvc to begin with? Just use flexable duct the entire way? Or use rigid duct work if you feel its a better job.

[jimbo]

No problem with the PVC duct. The fan may not have enough "oomph" to operate a second flapper, and it is not really necessary.

Dumping warm moist air under the soffit often leads to rotting problems. It is preferred to go through the roof, or through a gable end or the side of the house, but not under the soffit.

[Chris75]

No problem with the PVC duct. The fan may not have enough "oomph" to operate a second flapper, and it is not really necessary.

Dumping warm moist air under the soffit often leads to rotting problems. It is preferred to go through the roof, or through a gable end or the side of the house, but not under the soffit.

With the correct soffit cap, I dont see the problem your describing, and through the roof is the LAST spot I would vent an exhust fan. IMO of course.