Bathroom Fan/Vent Roof Cap Question

last year

I am putting in a new bathroom fan/vent. No fan currently. Since I have demo'd the shower insert to put in a new shower I am also adding light and fan. The situation is as follows:

(1) The ceiling is vaulted 12+' at apex.

(2) The ceiling is beam and wood, tongue and groove 1" planks. Then 1" foam/poly insulation/vapor layer, and roofing material (composite shingles). In all ~3" thick.

(3) There is no power/conduit in/through ceiling as there are no voids.

(4) The only power and switch location is on an interior wall; the wall where the shower plumbing is located.

(5) I have placed switches and run power up that wall off a GFCI circuit for light and fan.

(6) I have purchased a Panasonic FV-0510VS1 "WhisperValueDC" ventilating fan as it is thin enough to mount within a standard 2x4 stud wall and rated for wall installations.

(7) The fan has a 4" oval conduit mount, for which I have a 4" to 3" rigid adapter - and 3" rigid ducting.

(8) I plan to mount the fan approx 12" below the roof line in the wall which is approx 2' below the roof apex.

The challenge is that I am unsure of what roof cap to use and how to best attach the ducting given (a) I cannot holesaw a 4"+ hole as that would exceed the diameter of the wall and placement (3 3/2") within it; (b) the thin ceiling/roof combination does not allow for any wiggle room for a 3" to 4" adapter required to fit most standard 4" vent cap systems; and (c) there does not seem to be a roof cap vent for 3" ducting other than the type for pvc/plumbing vent stacks etc.

Am I missing something? Any ideas on caps or other solutions are appreciated. The other option is to abandon the fan entirely. There was no fan previously which was not a big problem as the bathroom is huge with high ceilings, but the shower was also enclosed in a full shower stall which I am now opening up to above, so in theory there will be more steam moving out of the stall toward the ceiling instead of condensing on the interior of the shower.

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Comments (2)

PRO
PPF.
last year

https://www.homedepot.com/p/Broan-NuTone-Roof-Cap-with-Built-In-Damper-for-3-in-or-4-in-Round-Duct-in-Black-636/202191718
0
Larry Arabia
Original Author
last year
Thanks PPF, I saw those. They say its is for 3" and 4" but it has a 4" hole and no sleeve mechanism. So my 3" duct penetrating through the roof will have to be enlarged above the roof cut and somehow joined to the receiver in the vent cap. There is <3/4" clearance between the base and the 4" receiver hole in the unit to accommodate a reducer without having to cut 4" into the roofing deck to make room. Reducers with clearance to join both ends would need 3-4".

I can either fashion something and tape it all up and hope for the best or I can simply extend the 3" pipe into the 4" receiver as far as possible and hope that the general seal around 3/4 of the base of the unit is enough to allow the venting air to activate the baffle and exit without too much bleed.

The unit also seems to have a really small base which does not provide much flashing surface to mount under the shingles. May not be a concern but it does seem to be narrower than other models. Thanks for the suggestion. I will have to think on it some more.
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In my opinion, it's a DIY project. I did three of my own bathroom fans, and one was in between levels of the house. The first thing I noticed is that you have missing insulation between these two fans. Another missing item is insulation that should wrap those ducts for the fans. I don't know what your area is, but I've heard around here that it's not generally recommended to join two fans to one vent, but if it must be done that the joint should be close to the exhaust vent itself. Yes, those bends are certainly going to be one source of problem. The vent on the left of your picture also looks like it still has an old 90Â° elbow attached to the new duct. If properly done, you would have a roof vent for each fan. The ducts would be composed of rigid ducting. This is available at Home Depot and Lowe's. You should use foil tape to seal the connections. Lastly you would need to wrap the ducts with insulation (foil backed insulation rolls are easy to find). Don't forget to locate your missing insulation that should be laying between those fans!
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Bathroom Fan/Vent Roof Cap Question

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Larry Arabia
Original Author

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Bathroom Fan/Vent Roof Cap Question

Comments (2)

PPF.

Larry ArabiaOriginal Author

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Larry Arabia
Original Author