I need to modify my bathroom venting

[Guido]

I have 2 bathrooms on the main floor (upstairs) venting through the roof, but each vent stack in the attic stops about 4-6 inches below a regular, square roof vent.

When I replace my roof (soon) I need to fix this. What's the best/easiest way:

1) Continue the stack straight up, and relocate the square roof vent.
or
2) Leave the roof vent in place and relocate the bathroom vent. This would require putting a couple elbows in the pipe.

Also, what I don't get is since roof ventilation is important in winter to prevent ice dams, etc. how do the vents work when covered under 5" of snow?

[Phelps]

Guido,

Repost this in the plumbing forum here. There are licensed tradesmen there that will be glad to help you.

[Wgoodrich]

I am taking it that you are talking fart fans in bathroom that run just short of a roof vent. Exhaust fans were installed in this manner in the 70s as accepted practice. Problem is two fold. The made the exhaust fan vent just short of the roof to dissapate into the attic with the intent of the warm air rising and being sucked on out the roof vent. If they had run the vent on through the roof the cold would have condensated the steam of a shower back into water and the water running back down to the exhaust fan damaging the fan and ceiling around the fan thus being the second problem with this design.

The code requires exhaust fans to be vented to the outside. That is all the Code says. There are many ideas how to do that across the nation.

If your exhaust fans are not having a moisture damage problem the design is working why fix what ain't broke. Love saying that, mom was an english teacher and drove her crazy ! Ha Ha. Kids ya know.

Now if you are having a ceiling stain problem or having a rusted exhaust fan problem then I suggest you turn the vents and vent them through an exhaust hood out the side wall of your house to meet the code.

Remember to keep these vents level. If you create a dip in a horizontal vent line and the steam from the shower is sucked to go out the dip will catch that steam and cause it to turn to water and collect in those dips again causing a problem.

If you run the vents too long vertically the steam cools turns to water and runs back down into the vents.

If you can read the above a minor mistake in exhaust fan venting can cause a lot of heart ache later down the road. Be careful and install them correctly to last a long time without trouble.

good Luck

Wg

[Guido]

Guido,

Repost this in the plumbing forum here. There are licensed tradesmen there that will be glad to help you.
Sorry, I should have specified - I'm talking about the electric ceiling fans in the bathrooms. Wgoodrich guessed it right.

[Guido]

I am taking it that you are talking fart fans in bathroom that run just short of a roof vent.
Exactly!


If your exhaust fans are not having a moisture damage problem the design is working why fix what ain't broke.
I'm not having a problem, I just thought it was code to vent through the roof to eliminate moisture buildup in the attic. The home inspector I hired said I should get it corrected when re-roofing. The house is 45 yrs old. I try not to use the fan in the winter, because I assume if I did it would simply vent into the attic since the roof vent would be covered with snow.
The vent pipe is insulated.


Remember to keep these vents level. If you create a dip in a horizontal vent line and the steam from the shower is sucked to go out the dip will catch that steam and cause it to turn to water and collect in those dips again causing a problem.

If I'm forced by the roofer/code to exit out the attic, I'll ask the roofer to put a stack as close to the existing roof vent as possible and I'll connect it to the existing stack from the bathroom with a flex pipe and insulate the pipe. I'll make the bends as gradual as possible.

But like you said - there hasn't been a problem, so should I even bother? Since I'm redoing the roof I don't want to miss this opportunity.

[Phelps]

They sell insulated bathfan ducting for the purpose of thwarting that condensation problem.

Me and a work partner I had 15 years ago, when we were doing city housing bid jobs, got called to this house where the bath fan was not exhausting. We went up in the attic only to find a long run of uninsulated flex bathroom duct and it so condensed that it filled up SOLID with water which turned to a block of solid ice in the flex!!! It was like trying to move a 100 pound python snake! I can't remember if we used insulated flex, then, or buried it under the existing attic insulation. I think we used the insulated flex on this job. We did several such fix-it jobs. One in particular had like a 40 foot run of flex going across the attic, ontop the insulation. Never seen anything like that before. They must have had this thing against roof vents because they ran it that whole way to vent it out the wall.

[Guido]

If I need to fix it, I'll still run it through the roof but with a dedicated stack so my horizontal run will only be a couple feet to clear the existing roof vent. And I'll make the "horizontal" part as vertical as possible.
I'll look into the insulated ducting, otherwise it's no big deal wrapping it myself.

How is the stack secured to the roof? Reason I'm asking is the roofers I talked to said they will install the stack and flashing, but won't go in the attic for the flex pipe connection. That's no problem for me as I can connect the flex pipe, but if they install the stack from the top will it slide down the hole unless supported somehow in the attic? Or does it get supported from the top?

[Phelps]

You are calling it a "stack". It's not so much a stack as it is actually a vent hood, like dryer vents have. The hose or piping connects onto it. The vent hood works like any other rooftop vent that has a flange on it. Shingles have to come up. You set the top 2/3 or so of the vent hood on the tar paper and the bottom 1/3, about, will be on TOP of the shingles. The top 2/3 of the hood's flange gets covered by the shingles. This all can be described in greater detail or you can look up some website that should show you how this is done. Or, someone working the builders desk at a home center could show you one on display that shows how it looks.

I would use the insulated flex if it were me, and make the run between fan and roof vent fairly taut. Not super taut, but taut enough that it can't sag weird. If you go solid duct, you will have to wrap the duct in insulation. I have already had to go up in attics and do this on 4 plexes already, where the water condensed from the cold metal duct and ran down back into the fan and started wrecking the ceiling around the fans. I went up in the attic with an 8 foot batt of insulation (for each one) and wrapped it aound the pipe so the seam was vertical. Then I used twine or plastic ties to band around each one. That solved the problem.

[Guido]

Oh - thanks for clearing that up. I thought the whole point was to get the exhaust above the snow line, but if all that is required is a vent hood, then it makes life simpler. I'll get the builder to install the vent, put the shingles, and I'll connect it from below in my spare time.

Here is a photo of the stack. Stupid question, but I don't recognize that type of insulation with the paper wrapped around it - it's not asbestos or anything like that is it? The house is mid 1960's, but I don't know if that pipe was installed after or not. I don't think it is, but you guys know a lot more than I do.

[Phelps]

Looks like plain old kraft paper covered fiberglass insulation to me. That works. Doesn't look like the neatest job in the world though. :)

Regarding roof vents getting covered up with snow: Ever drive by houses that have those low profile 'gravity vents' up on the roof? Those are those square shaped ones. Some new homes have tons of them up on the roof. You will usually see the snow melted around them.

Vent hoods for dryers and exhaust fans are put up on roofs all the time, in snow country.

[Phelps]

... but if they install the stack from the top will it slide down the hole unless supported somehow in the attic? Or does it get supported from the top?

It is supported from the top by the flange of the vent hood (stack as you call it). You can take insulated flex and angle it up to the vent hood if you like. No need for elbows. *IF* you went the route of solid pipe, you could offset with angled couplings, to get away from having horizontal runs. Then insulate the pipe like your photo.

Oh. They also sell that foam tube stuff that is split lengthwise and has a ribbon of plastic you tear off. Upon installation, you squeeze the seam together and it sticks. You could use that as well I supose. It might be a little pricey though. I think they might have it in 4 inch i.d.. It is the same stuff that you see on outside a/c units that the refrigerant goes through, to insulate the copper tubing it is in.

If this were me though, I think I would just be going the route of the insulated flex. It works and is quick and easy and you can easily offset it.

[Guido]

If this were me though, I think I would just be going the route of the insulated flex. It works and is quick and easy and you can easily offset it.
I think I'll do this. Unless it's 5X the price then I'll get non-insulated flex (if it exists) and insulate it myself. There will be no horizontal runs - max 45 degree off vertical. Once they install the vent I can properly measure the dia and length I require.
Thanks for all the help!!!

[Wgoodrich]

Guido I advise you to contact you local AHJ [government inspector aka code enforcement]. Reason is your home inspector has no authority to say what is outside. This subject if a great example of two inspectors with different rulings. Go to one jurisdiction and the code enforcement AHJ will rule venting near the roof vent meets the Code. Then go to the neighboring jurisdiction and the inspector AHJ will fail you because you did not meet code requiring you to physically pass through to the outside to meet his ruling on the subject. This is the contractor's nightmare. Chewed out because you did it in one jurisdicton and chewed out because you didn't do it the next day in another jurisdiction with a different AHJ.

This is what I wish we could resolve for the normal contractors creating uniformity. Education is our only chance to get that done.

Call you code enforcement officer, what he or she rules will overrule you home inspector's thoughts on the subject. What you have may be what your AHJ requires.

Let us know the results of your AHJ ruling.

Good Luck

Wg