bathroom and range hood vent duct penetration?

[Will Schaefer]

Hi All, I'm amid a DIY bathroom renovation in a 1908 brick rowhouse, Washington, DC. I want to add venting to the bathroom on the second (top) floor and the kitchen range hood on the first floor (the kitchen is directly below the bathroom). There is very limited wall space at this end of the house to allow a vent through the outside wall (close to chimney, doors, windows, neighboring rowhouse). There is also virtually no roof edge eave/soffit to speak of (the rain gutters are practically mounted to the wall). So my hope is to be able to hire my roofer to run both vents through my flat EPDM membrane roof. Finally, there happens to be a roof access hatch through the bathroom ceiling--aesthetically it's unfortunate; practically it is convenient to not need a 40'+ ladder...

My questions are two:

1. Given I am trying to limit duct lengths, what limitations do I (or my roofer) need to find out as to how close together roof penetrations such as these (soil stack vent pipe, roof access hatch, chimney, kitchen exhaust duct pipe, bathroom exhaust duct pipe) can be?

2. I assume I should insulate both ducts in the crawlspace. If so, what type of insulation for the range hood? May I use polyurethane foam-in-a-can for this?

Thanks in advance for your thoughts!

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[John Kogel]

Hello Will. I think you are on the right track. You may be able to run the range hood vent pipe up an interior wall. I'm sure someone will post the minimum distances for the exhaust vents. One restriction I can think of is clearance for snow pack. You may need to add a pipe extension above the roof to meet the local standards.

We think by "crawlspace" you mean the attic area above the bathroom?

There are pipe insulation wraps you can buy for that. The cost is minimal, so use the right stuff. Don't use plastic "duct tape" for the connections. It will dry out or melt in the heat and let go. Foil tape costs more but works much better, or use clamps to attach the vent pipes to the roof flashing.

If the roofer has experience with EPDM, he will know to use the correct flashings and sealant for the job. That is the one area where you don't want to cut corners. Good luck.

[Bob Elliott]

I see no reason there should be a clearance requirement as the exhaust from neither is toxic and they usually have vent flaps.'
Just do not allow the roofer to cheat by dumping into the attic which can cause issues others will tell you about.