Do to an upcoming addition, I need to reroute the ductwork for my bathroom exhaust fan and for my dryer exhaust, both 4" round metal duct. I don't have a lot of options for where to run the ducts given that 1) I live in a rowhouse, so only two exterior walls, 2) the ducts can't be longer than 25', 3) the ducts can't exhaust within 3' of any windows or door. As such, I need to run the ducts perpendicular to the ceiling joists and must build a soffit.

I am looking for some advice on how to build the slimmest, lowest profile soffit possible. The soffit needs to run along the basement bathroom ceiling, so I would like for it to be attractive and small as possible.

So, I would love advice on the following (or anything you think is helpful)

1) Where should I locate the soffit in the bathroom to be most attractive and least obvious? I have included a drawing of the bathroom. Because of windows and door, it would be best for the vents to exit somewhere in the vicinity of the tub. Also, it is a tub/shower.

2) How can I build it to minimize its size. If I use 2x4 or 2x3 material, it's going to be big!

3) How much space do I need to leave between the two ducts to make sure I will be able to terminate them on the outside?

Any other thoughts or ideas would be VERY much appreciated!


http://www.diychatroom.com/attachments/f19/19994d1272466364-slim-soffit-ductwork-basement-bathroomlayout.jpg

What about using a 2"X6" rectangular pipe for the exhaust?

You can use an adapter to change from the round to the flatter rectangle and it would still(I think) move the same amount of air.

Maybe someone in HVAC or plumbing can answer as well.

I am not sure what the 'change' is in the layout,it's cut short.Can you explain the 3'X6" and the dotted lines please?

Thanks KBC.

I had actually thought about using rectangular ductwork, but the issue is that I actually need to run two ducts, one for the dryer and one for the bathroom fan. I think I'd end up in much the same situation with the rectangular duct, no?

As for the dotted lines and the 3'6", it is really unrelated to what's going on here, I just pulled the drawing of the bathroom from a larger set of plans. Basically what I am trying to figure out is, since I need to run this ductwork/soffit through the bathroom, is there a most logical location for it? Someplace where it will seem more natural, etc.

I can't seem to find any clearance requirements for dryer venting. There would be none for exhaust fan venting. Are you sure about exhaust fan piping size, don't think its 3". Best location for soffit would be next to wall. Lowest profile would be to put a 2x2 nailer on wall and ceiling. Attach a 2x2 to inside, bottom edge of what ever you are going to use to make soffit out of, then screw that assembly to ceiling 2x2. Attach bottom covering to wall 2x2 and to 2x2 on inside bottom edge side of side material.

Since you probably have plaster walls and ceiling I would use Hardie board to build soffit since neither of these are combustible and not worry about clearances.

All this assuming an electric dryer and venting is for moisture only.

How high is ceiling, might want to consider dropping entire ceiling.

Harold-

Thanks for weighing in on this, much appreciated.

Let me give a little bit more info. First, it is a gas dryer, not electric, but I cannot find any clearances for a gas dryer vent either. Do you know of any?

Second, in this particular area, we have plain old drywall, well, sort of. But I would prefer to use drywall to match.

The ceiling is 84" from floor to ceiling. From tub floor to ceiling is 82.5". I recently learned though that the current basement ceiling is furred down with 2x4s on their bellies from an 1/2" original ceiling of some sort (some sort of pre drywall, tongue and groove plasterboard). So, currently there is 1/2" of drywall, 1.5" of furring, and 1/2" of original ceiling material. The distance then from floor to the bottom of the joists is 86.5" and from tub floor to the bottom of the joists is 85".

So, I can certainly remove channel a path through all of the existing material wherever I decide to run the duct, gaining the extra 2.5", right?

So, here is a brief diagram, aesthetically, am I better off going with the blue option or the red option?

Also, the "pre drywall, tongue and groove plasterboard" has me just a tiny bit worried about asbestos (wondering if this is why the previous owner furred it down). How can I go about figuring that out?

The age of the house would be a primary sign as to the use of asbestos, or simply horse hair plaster and lathe.

"From the tub floor to the ceiling is ..." ,Is there a reason you added this dimension?Header clearance,perhaps?

It would seem you have lots of clearance for the rectangular pipework now(with the maximum of 4" clear)or if you prefer to use the round,as Herold asked,,are you sure the vent pipe from the bathroom is 3" not 4"?(Note:It isn't unheard of to cut small recesses in the base of joists to accommodate ductwork,if the pipe from the dryer has to be 4" and you only have 3.5" I have seen many with notches in them)

A header doesn't seem necessary anymore of you can bury the pipes.

If it IS necessary,are you allowing for the steam in the shower to be vented?Is the exhaust fan IN the shower area? otherwise you'll be trapping moisture in the shower itself.

You have several problems with your plan.

1. If you build a soffit, it must still maintain a minimum of 6'8" (80") of clearance above any bathroom fixture to meet most codes.

Since your floor-to-ceiling height is already a short at 7'
(84"), adding a soffit anywhere is going to give you head room problems in this bathroom especially if located above the tub.

2. Most mechanical codes also do require a minimum 3' of clearance for vent terminations from openings on the outside of the building as you have indicated. This is to prevent odors and moisture from dryers and bathrooms from re-entering the building.

My recommendation therefore is to try to run the ducts vertically up through soffits built in a closet or other inconspicuous space to get to the attic, then terminate the ducts through the roof or eaves.

And remember: the 25' code recommended length for dryer ducts can be lengthened if the dryer manufacturer permits it.
Most dryer manufacturers permit runs of 35 feet or more less reduction for 45 and 90 degree bends.

Thanks guys for the additional input.

KBC- The home was built in 1933, although I have no idea when the basement ceiling was done. The material is certainly plastery and fibrous, but no idea. Any thoughts? Also, not sure where Harold got the 3" duct idea from, but they're both definitely 4", as my post explains. I'd rather not notch my joists and certainly not at much as would be necessary to bury this ductwork.

Manhattan- I am very much aware of the need for 6'8" clearance, it is the primary reason why this post focuses on a slim soffit design. Please see my last post in its entirety, yes, the ceilings are 7', but they are also furred down a total of 2.5" from joists, so I actually have 6.5" to work with, which should be enough, no? The whole purpose of this endeavor, as I indicate in my first post is to be in compliance with the 3' rule. Running it through the roof is not an option, unfortunately, I'd have to run it horizontally 15' and then vertically ~30' to make it work, with a number of 90s.

My primary question really still pertains to how to build the lowest profile soffit possible. I am glad Harold raised the issue of pipe clearance, does anyone know how far dryer exhaust duct must be from combustibles?

Dryer duct is zero clearance to combustibles..

Did you note that this is a gas dryer? I'm not familiar with gas dryers and have not been able to find anything on clearance for ducting.

Manhattan-

Thanks for the help, but I am afraid your confusing things a bit. Yes, floor to ceiling is 84", but floor to the bottom of the joists is 86.5", because the ceilings have been furred down. So, if I channel out the existing ceiling where the ducts will be up to the original joists, then I have sufficient room for a 6.5" soffit while still respecting the 80" minimum clearance. Making the minimum clearance is totally possible. Not sure where you got the idea that it won't be permitted, it absolutely will be as it is part of a much larger addition to the home.

Also, I have confirmed in the manual that dryer duct is zero clearance from combustibles. So, no worries there!

So, question remains, how to make the most slim, low profile soffit.

Also, if anyone has thoughts on testing for asbestos, would be great.

Remove old ceiling, notch joist, use oval ducts. Technically, you won't make minimum but you will be close. Seriously doubt inspector will notice much less reject.

Yep, going to scratch the addition over a dryer vent. Thanks.

I am going to channel the ceiling (no notching of the joists), to mitigate the furring. I will install a soffit, 10" wide by 6" tall. The room ceiling height will be 7' and the soffit will be 80.5", so just fine.

Thanks.

If zero clearance is allowed, set bottom of soffit 1/2 inch below duct. Drop area in tub to back wall and soffit will disappear as a dropped ceiling.

Chuck