Waterproofing 6 inch wall cap through vinyl siding

[tobaccorancher]

I am installing a bathroom exhaust fan above a shower to fix mold issues. The most direct vent location is through the gable wall. I looked at roof exhaust, but roofing contractors were hesitant due to the age of the roof (20 years)

I purchased the Broan 641 6 inch wall cap. The flange on this cap is 9 X 9. I want to install this right so that I don't get rainwater behind the vinyl siding.

I have not yet found a J-block which is close to this size. I have seen reference to fabricating a block using 5/4 inch Azek, running house wrap over the top edge of the Azek, flashing, and installing J channel around the block.

What is the best way to rain-proof this cap? To make matters worse, the house currently has no house wrap, but I am planning on installing house wrap when I install this cap.

Thanks,
Andy

[Mark Parlee]

Best to go thru the gable when you can.
I would use a schedule 20 PVC pipe for the vent piping. Elevate is a little at the fan and run it downhill over the ceiling joists to the gable. Connect to the PVC with a short length of flex. after you are done in the attic cover the pipe with insulation. If there is any moisture in the pipe from condensation is will drain toward the exterior.
The PVC block is a good idea and wrap it with J.

BTW Rainwater always gets behind the vinyl siding that is why it is important to have everything sealed up and why a WRB is critical.

[tobaccorancher]

Thanks. I went to the siding distributor to look for a J-block and they did not have one big enough for this. So, I will make block out of PVC trim. I talked to the distributor about stripping the siding off that side of the house and putting wrap on and he said that would be a waste unless the whole house is wrapped. I may go ahead and wrap that wall anyway, but might wait until cooler weather to do it. I'll make sure the penetration has wrap so that I can continue down with wrap over time. None of the existing penetrations are blocked or flashed....they just put caulk around them. Amazing.

[Mark Parlee]

feel free to give me a call.
Info on my website

[Ted S.]

There are blocks made for electrical meters, I think I have seen them made by Ply-Gem. Might actually be on the larger side then what you need, but probably work just fine. If you can find a dealer for Ply-Gem I would call them.

[Bill Robinson]

Even if the rest of the house does not have an QRB the new penetration you are making will certainly provide a leak location you can avoid by using a block.