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Cost to vent bathroom exhaust fan to the roof

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  • Mar 6th, 2013 12:03 pm
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[OP]
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Sep 7, 2008
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Cost to vent bathroom exhaust fan to the roof

Folks, my sister just bought a house and found out one of the bathroom fans on the 2nd storey is not vented outside. It blows into the attic. Can you please tell me how much it cost for both part and labour to vent this to the roof? If you are in the trades, please feel free to PM me for the cost. Please do not discuss the legal matters and such, I am just looking for advices on the costs.

Thanks in advance
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Oct 22, 2007
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Cost will be between $150.00 to $1250.00 depending on about 22 variables. In other words to get a better informed accurate estimate someone needs to visit the home and go into the attic and get much more information.
[OP]
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Sep 7, 2008
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Thanks for the prompt feedback! I don't know there are that many variables :-) I thought these would be standard cost to run a duct line between the fan and roof vent. So I am thinking it requires parts such as ducting, roof vent, duct insulation wrap, all caulking/sealants...etc and of course the labour involved. Am I missing something?
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Here is my take on the situation;

If someone vented the bathroom fan into the attic which is not proper then what else has been done incorrectly? If the ducting is the flexable type that I would also changed to rigid, are there too many bends. does the present fan have enough cfm to exhaust all the way to the outside, are the present ducting sealed, the right size, is the power requirement or all of the present installation up to code, I could go on and on, but it's best to get a written estimate.

EDIT:
I'm sure some will chime in and say, "hey, I got mine for for 375.00" but you're not comparing apples to apples therefore not much use to you, since you haven't even given a location let alone more details on length of run, amount of attic insulation, whether vapour barrier is needed etc.
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Apr 4, 2009
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As venting to the roof, involves cutting a hole in the roof boards and disturbing the shingles, I would suggest doing this as part of replacing the roof shingles.

Just tell the roofers to add a bath room vent "here", and they will add a cut a hole in the roof boards, add a bathroom vent cap/housing and seal it up properly and shingle around it.

Then it should be as simple connecting the fan exhaust to the vent cap/house using an insulated flexible tubing/conduit in the attic.

This really doesn't have to be done ASAP. Normally, the roof/attic vents itself a bit, so it is not as if all the moisture just builds and builds inside the attic. (Can OP go up into the attic and verify there is no mould around the bathroom fan? Or that it is not burried under 2 feet of insulation.)
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Feb 16, 2013
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"It blows into the attic" and so what? why worry about it? sounds like it would work that's why they did it like that. A hole in your roof is never a great idea. You can open a window too now and them.
[OP]
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Sep 7, 2008
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Perhaps I could clarify a bit here. There is no ducting, I climbed into the attic and saw the fan is not connected to anything. The house is fairly new. I think the trade installed the fan and forgot to vent it to the outside, And of course, building inspector missed this. So I would think, to vent it outside, someone needs to cut a hole on the roof right above the fan and install a roof vent, run a ducting from the fan to the vent, caulk and seal it? Am I right or it is not that simple? Thanks again for your help!
[OP]
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Sep 7, 2008
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Busybuyer888 wrote: As venting to the roof, involves cutting a hole in the roof boards and disturbing the shingles, I would suggest doing this as part of replacing the roof shingles.

Just tell the roofers to add a bath room vent "here", and they will add a cut a hole in the roof boards, add a bathroom vent cap/housing and seal it up properly and shingle around it.

Then it should be as simple connecting the fan exhaust to the vent cap/house using an insulated flexible tubing/conduit in the attic.

This really doesn't have to be done ASAP. Normally, the roof/attic vents itself a bit, so it is not as if all the moisture just builds and builds inside the attic. (Can OP go up into the attic and verify there is no mould around the bathroom fan? Or that it is not burried under 2 feet of insulation.)
The roof is almost brand new. My sister has since then stopped using the fan after learning that it is not vented to the outside. I went into the attic and found the open end buried in attic insulation. Would this affect the fan if we turn it on.
3foxes wrote: "It blows into the attic" and so what? why worry about it? sounds like it would work that's why they did it like that. A hole in your roof is never a great idea. You can open a window too now and them.
are you sure it will not affect the fan since the open end is buried in attic insulation?
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No it is not that simple because someone has to go up on the roof and install the flashing and fix the roof now there is hole in it. Does it work now at all, maybe it's okay? Or are you sayings it just like a fake vent? Like i said you might find just as simple to open a the window now and then, assume there is a window. I say that because i never put the fan on personally. It's like if there is 3-4 showers a day there you will have a problem. How much humidify builds up when you take a shower?
[OP]
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Sep 7, 2008
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3foxes wrote: No it is not that simple because someone has to go up on the roof and install the flashing and fix the roof now there is hole in it. Does it work now at all, maybe it's okay? Or are you sayings it just like a fake vent? Like i said you might find just as simple to open a the window now and then, assume there is a window. I say that because i never put the fan on personally. It's like if there is 3-4 showers a day there you will have a problem. How much humidify builds up when you take a shower?
No, the fan is working. It is just not being vented to the outside. As I mentioned, the open end of the fan is buried in attic insulation. So, if we use the fan, would the attic insulation affect the fan, and the most important thing is will this causing mold build-up?
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hard to say if it would cause a problem or not, depends on how many showers you take per day, but that is not they way it is intended to work you are absolutely right. Since you just bought the house i would call up the sellers and give them some hell, they will probably fix for you for free.
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3foxes wrote: "It blows into the attic" and so what? why worry about it? sounds like it would work that's why they did it like that. A hole in your roof is never a great idea. You can open a window too now and them.
This is a big no-no. You are blowing warm air which contains moisture, which in turn ends up in your attic, thus causing moisture issues, including mold.

OP: Just because it's currently vented to the attic, doesn't mean you have to vent it out through the roof. That's actually not recommended at all. You should be redirecting it from where it enters your attic, then through the side of the house.

This video is exactly what you need to do:

http://www.thisoldhouse.com/toh/video/0 ... 38,00.html

You'll notice in the video, it even recommeneds against venting through the roof. If you are slightly handy, this is a fairly straight forward job.
tockty wrote: No, the fan is working. It is just not being vented to the outside. As I mentioned, the open end of the fan is buried in attic insulation. So, if we use the fan, would the attic insulation affect the fan, and the most important thing is will this causing mold build-up?
If the open end of the fan is buried in the attic insulation, that means the fan isn't doing much at all. You might as well not have a fan at all since all that warm air is still being trapped in within the bathroom since it hasn't gone anywhere due to the blockage.

How do you know this unless you have already crawled into the attic and have seen this in person? If you've already done that, you're already half way there in doing this job yourself, as you can see from the video I posted.
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[OP]
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Sep 7, 2008
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gheart008 wrote: This is a big no-no. You are blowing warm air which contains moisture, which in turn ends up in your attic, thus causing moisture issues, including mold.

OP: Just because it's currently vented to the attic, doesn't mean you have to vent it out through the roof. That's actually not recommended at all. You should be redirecting it from where it enters your attic, then through the side of the house.

This video is exactly what you need to do:

http://www.thisoldhouse.com/toh/video/0 ... 38,00.html

You'll notice in the video, it even recommeneds against venting through the roof. If you are slightly handy, this is a fairly straight forward job.



If the open end of the fan is buried in the attic insulation, that means the fan isn't doing much at all. You might as well not have a fan at all since all that warm air is still being trapped in within the bathroom since it hasn't gone anywhere due to the blockage.

How do you know this unless you have already crawled into the attic and have seen this in person? If you've already done that, you're already half way there in doing this job yourself, as you can see from the video I posted.
Many thanks gheart008. Yes I did crawl up there to find out. It wasn't a pleasant experience but I managed. I will take a look at the video to see if I can manage it. Another question? When I was up there, I saw another fan belonged to another bathroom nearby vented to the roof, so my question is "Is it easier if I could connect this to the ducting of that fan?" it is about 10Ft apart between the 2 fans.
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tockty wrote: Many thanks gheart008. Yes I did crawl up there to find out. It wasn't a pleasant experience but I managed. I will take a look at the video to see if I can manage it. Another question? When I was up there, I saw another fan belonged to another bathroom nearby vented to the roof, so my question is "Is it easier if I could connect this to the ducting of that fan?" it is about 10Ft apart between the 2 fans.
No. Do not connect that ducting together. You will need a separate duct/vent for each of those fans. Every additional length and extra corner you add to ducting will reduce the amount of air the fan can move. Also, imagine that some cheap bathroom fans don't have backdraft 'gates', so you can be blowing stinky air from one bathroom to another.
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3foxes wrote: "It blows into the attic" and so what? why worry about it? sounds like it would work that's why they did it like that. A hole in your roof is never a great idea. You can open a window too now and them.
:facepalm: Wow.
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Nov 9, 2008
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DarkCanuck wrote: :facepalm: Wow.
My sentiments exactly. I would hate to see his house if he thinks exhausting moist humid bathroom air directly into an attic isn't a problem.........
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ViperZ wrote: No. Do not connect that ducting together. You will need a separate duct/vent for each of those fans. Every additional length and extra corner you add to ducting will reduce the amount of air the fan can move. Also, imagine that some cheap bathroom fans don't have backdraft 'gates', so you can be blowing stinky air from one bathroom to another.
+1. It's not only backdraft that's the issue, it's also the size of the duct. Most likely with the one bathroom that is already vented correctly, the duct size was only meant for that one fan. If you tie two fans to it, you could imagine what would happen if you had both fans running at the same time. The size of the duct wouldn't be able to accomedate the extra volume of air being produced by both fans.
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[OP]
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gheart008 wrote: +1. It's not only backdraft that's the issue, it's also the size of the duct. Most likely with the one bathroom that is already vented correctly, the duct size was only meant for that one fan. If you tie two fans to it, you could imagine what would happen if you had both fans running at the same time. The size of the duct wouldn't be able to accomedate the extra volume of air being produced by both fans.
Thank you all for the advices, folks! Much appreciated....
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Feb 16, 2013
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I said it wouldn't be a problem if you didn't use the fan or have showers. Do you people not read english?
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Mar 18, 2010
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3foxes wrote: I said it wouldn't be a problem if you didn't use the fan or have showers. Do you people not read english?
So don't use the fan or take a shower? :facepalm:

Do you not understand that what you are saying is obsurd?

My god.... When you have a house, you make sure it's done right. Vent it outside, there are several ways to do this, to the roof, a soffit, whatever, just don't leave the thing hanging loose in the attic and build up moisture. I bought a house last summer and have been renovating since. I had a similar experience, the previous owner had the fan blowing into the attic as well from the main bathroom, and let's just say I had to get the mold it created encapsulated.

The best advice for anything in the house, is do it right, and it'll pay for itself in the long run. Shortcuts only hurt you or the next owner.

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