adding bath fan, and weird ceiling issue

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Hi all,
Finally got up into my attic today to poke around and see what was what. Yes, I bought my house two years ago, but never had a reason to go up into the attic before. The reason I was going up there was to assess what I had to do to add a ceiling fan in the bathroom.
Good news: ceiling of 2nd floor appears to be framed with 2x6's, and I mean real old-school 2x6's not what passes for same today. Also roof was scratch built, no trusses, so even though I have a tiny house, the attic space could actually be usable for storage if it became necessary.
Bad news: as is normal practice, the ceiling joists run crossways across the house and tie into the rafters, unlike the lower floors where the 1st and 2nd floor floor joists run the length of the house (spliced above a load bearing wall next to the central stairwell.) I was surprised to find this, however, because it makes my proposed fan install more difficult, and because I actually had reason to believe that it wouldn't be like this (see below.)
Why I thought my house was framed oddly:
In the master bedroom, the ceiling has several parallel cracks running exactly parallel to the long dimension of the house. They are very evenly spaced about 13-14" apart. I ASSumed that this was due to wet insulation (the roof was replaced by the POs of the house) causing excessive load on the ceiling between the joists, but the cracks are running perpendicular to the joists. Also the insulation is bone dry, but that doesn't tell me anything as it's had several years to dry out. The wall/ceiling construction in this house is plaster over gypsum lath. Any ideas as to what this cracking could indicate?
Finally, my immediate issue and reason for being in the attic was to try to plan the install of a vent fan for the bathroom. Since I'd thought that the ceiling joists would run lengthwise, my initial plan was to simply install the fan between two joists in the bathroom ceiling, point the outlet towards the side wall of the house, and cut a dryer-vent type vent hood on the outside wall, connecting the two with a straight piece of duct. Obviously, since the joists run perpendicular to the direction that I suspected that they did, I can not do this, at least not easily (I'd have to cut a 4" hole in a 6" board until I got to the side of the house, which would probably indicate reinforcing each joist with angle iron or similar, that's a lot of work.) My house does not have any soffits at all - the roof ends just past the edge of the exterior wall, so I can't use a soffit vent. I do not want to cut a hole in the roof for a roof vent, as it is this weird pressed aluminum stuff that I guess is supposed to emulate the look of cedar shakes. So that leaves me back to my original plan which would be to go out through the side wall. But to do this now would involve two 90 degree bends in the ductwork (I suppose I might be able to get away with a 45 and a 90) and the ductwork would be above the joists meaning that I would have to then use insulated duct. No big deal, but would the extra bends in the ductwork cause an issue, and should I then uprate the CFM of the fan? The bath is 5'x7' including the bath/shower area (yes, it *is* a tiny house, why do you ask?) so I was figuring on a 50CFM fan, specifically one of these:
http://www.bathroomfanexperts.com/product.php?p=panasonic_fv-05vf2&product 1068
(this one was the one I was thinking I was going to use when I thought that the joists ran lengthwise, so I could hide everything below the top of the ceiling joists, should I ever decide to floor that part of the attic for whatever reason.)
http://www.bathroomfanexperts.com/product.php?p=panasonic_fv-05vq3&product 1054
(this one is higher profile, but quieter. If I have to run ductwork above "floor" level, I'd choose this one.)
thoughts, comments, concerns?
nate
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I don't think the extra elbows are going to affect the performance. But I noticed the wall mount fan on the link, have you considered that?
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Mikepier wrote:

I don't have enough room for a wall mount fan. The only exterior wall that isn't within the bath/shower area is almost completely taken up by a window.
nate
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Personaly I would not consider anything smaller than 100 cf as the purpose is to dry out as fast as you can . A bit of noise is small price to pay for better mold control and dampness control .
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jim wrote:

I'd thought of oversizing it, but after googling a little bit for a more precise sizing guideline including effective duct length it still seems that 50cfm is recommended for my size bathroom... (used two elbows, a wall cap, and about 10' of duct for my estimate - probably longer than it'll actually be) Has anyone actually installed a larger fan than recommended and if so did you notice any other downsides besides noise?
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I have 2 bathrooms. One is 5X6 with a 50 CFM Broan fan/light. No problems the other is 4X7 with an 80 CFM Nutone fan only. No problems
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wrote:

Well, we should have an 80 cfm in our bathroom, but ended up with a 150 cfm (I think, or maybe a 100). We're using it now in the beginning of a western New York winter, and I'm actually ok with how fabulously it sucks out the moisture. The room is not exactly cold, but there's also almost no moisture on the mirror. Ours is a Broan wall-mount, fyi, due to the house being built in 1930, etc., etc., and we're real happy with it. Hope the new paint job holds up!
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on 12/6/2008 1:44 PM Nate Nagel said the following:

http://www.bathroomfanexperts.com/product.php?p=panasonic_fv-05vf2&product 1068

You're not going to put a floor all the way to the junction of the attic floor joists and roof rafters, are you? I would suspect you would want to put a knee wall some distance into the room from that junction, leaving a long open area behind the knee wall running to the outside wall.

http://www.bathroomfanexperts.com/product.php?p=panasonic_fv-05vq3&product 1054

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willshak wrote:

I wouldn't bother. I'd need to actually raise the roof up 2-3 feet as well as build a dormer over the top of the stairs if I were going to make that into usable space (e.g. a kid's bedroom or half-bath for a master "suite") and it is still only accessable through the master bedroom closet (the closet includes the space above the ceiling of the stairwell, so it'd be somewhat trivial to put permanent stairs in.) In other words, waaaay more work than I wanted to get into.
I was really thinking more in terms of simply putting down some subfloor type plywood down the center of the attic, in case I wanted to shove some boxes up there, and I was going to keep the fan/duct below that level if possible just so I wouldn't knock into it with moving boxes around, is all. Not even thinking about finishing the "ceiling" up there. That wouldn't even be happening for quite some time as I have some rewiring to do up there; I'll probably just bring some half sheets of ply up there so I can move them around so I don't have to be so careful about balancing on the joists without working (I've heard that falling through a ceiling is a good way to ruin your holidays, and put a crimp in your sex life, for several reasons.)
nate
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Nate Nagel wrote:

Your crack / water mark lines run in parallel with the roof sheathing, no? If there were roof problems water would collect on the edges of those boards and drip off those edges, so the drip lines would be perpendicular to the ceiling joists.
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Pete C. wrote:

Good guess, but I doubt it. The roof uses boards, not sheathing.
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bath fans in a home are a waste of energy
in the summer, just open a window to let out the humidity after a shower
in the winter, you need the extra humidity anyway
remember that for every 100ccf of air that the fan vents out, another 100ccf of OUTSIDE air MUST enter your home someplace to replace it..
Mark
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I disagree with that. I had windows in my 2 baths without fans and it did not help. Once I installed the fans it was a lot better. Although I agree opening up the windows helps, especially when its cool and dry outside to get rid of the humidity faster with the fan.
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Mark1 wrote:

I strongly disagree. In my house, after a good steamy shower, you can see condensation dripping from the ceiling. There's some little patches of mold starting in the corners, but I'm not motivated to repaint until I get a fan installed. This is with the window open and a window fan running.
I'm not sure how the PO's were able to keep the bathroom nice. I suspect that they actually showered in the bathroom in the garage and never used the one in the house.
nate
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Your install with 90 deg elbows should be fine. If you want to get technical, you can google online and find a derating table that lists the feet equivalent of various components. You then add those feet equiv to the total run length, giving you the effective length. I've seen them in install instructions for range hoods. As an example, a hood might be spec'd to work with a max duct length of 30 ft. You have 10 ft of actual duct, two 90 deg elbows (5 ft from chart each), a 45 deg elbow (2.5 ft). That's an effective length of 22.5 ft.
I'd look at the install instructions for your fan to start. But for a small bath situated by an outside wall, the duct plus two 90's should be fine. The 5ft equiv for 90 deg elbows is I believe correct for larger round ducts for hoods. In new construction, I've seen them vented from a bathroom on the front side of a house all the way across to the back side of the house. Yours has to be a lot better than that.
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wrote:

Mark, you clearly don't live in western New York. Opening a window in the summer to let out the humidity DOES NOT work. And leaving the humidity in the winter at the rates that hot showers produce only creates mildew and peeling paint. Just understand that what works for you may not work for others.
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yep, whatever works for you...
but remember, the energy cost of the vent is NOT just the energy to run the motor, that is nothing.... you have to replace the conditioned air that is pumped out with cold outside air, and even that is not so bad if you run the vent for only a few minutes a day...to me the real deal breaker is that the vent slats do not close tightly when the vent is off, so even when the vent is off, there is air flow, you may not feel cold air coming in the vent, it may be warm air is going out, but every bit of that warm air going out is replaced by cold air comming in someplace else in your home... 24 hours a day.... that is not worth it to me
if that is worth it to you,,,fine...
and if you have that much moisture in the bath that mold forms in the winter during heating season, then I doubt that any vent is going to solve that problem anyway..
Mark
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So, you'd rather have your bathroom and other nearby parts of the house smell like farts after someone takes a dump, instead of spend a little bit of energy. These bath fans have flaps that close on the exterior vent and another flap at the fan. Sure, there will be some leakage, but it's not a big deal. Houses certified as energy star have them.
Also, I've seen bathrooms with paint peeling off because they didn't have a fan. What's that cost compared to the small energy loss of a fan? Even in more moderate climates, where you could open a window, what's the point? Under those condiions, the heat/cool loss of the fan is almost zero, because the outside temp is closer to inside.

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Nate Nagel wrote:

Boards are a type of sheathing. I presumed it's individual boards, not more modern plywood, though it may now have a layer of plywood as well if it was re-roofed.
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Pete C. wrote:

I understand, but that really doesn't explain what I am seeing. I don't see any evidence of water on the boards either, although if there ever was any it's been dry for several years. I guess it will just remain a mystery until I either a) find a good plasterer to redo the ceiling or b) get sick of looking at it and redo it myself with drywall.
nate
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