# Moisture- Should I vent roof for my small building or buy fan?  Conflicting answers.



## alanrudy (Jan 28, 2015)

I have a 120sq ft shed/building that insulation and drywall was added flush (instead of flat ceiling) to the ceiling to maximize height inside (please see pictures for hopefully good description).  I had an issue with few drops of water under the lights pictured when I took them off.  First, I thought the roof was leaking but after running a hose on the roof with no leak, the only other thing I'm thinking it could be is condensation.  This may have been an issue with the recent rain (from So Cal so doesn&#8217;t usually rain) so the difference between the cold ceiling and hot interior created it.  I&#8217;ve gotten conflicting reports on what to do:  One contractor told me I should vent the roof in some way.  The other said a vent would expose the drywall/insulation to the elements and to just get a portable fan/heater so air/temperature could be regulated since it&#8217;s only 120sq ft.  I like the fan/heater option since it's something I was going to buy anyway for hot/cold times, but maybe the right way is to vent it.  What should I do?


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## alanrudy (Jan 28, 2015)

Here are some more pictures, could really use advise.  Thanks in advance.


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## inspectorD (Jan 28, 2015)

Anything could be happening there. I guess you could install ridge vent..but it may not fix anything. 
What kind of insulation, and how thick?
Is there a vapor barrier like paper faced, or plastic?
Do the lights have insulation behind them in the ceiling?..or is there an air space? ( This is my WAG)
Do the lights give off any heat?
Is there tar paper, or ice and water under the shingles?
How long ago was the sheetrock, and tapping finished? 
How big was the temperature difference?

Its a start...


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## alanrudy (Jan 28, 2015)

Thanks so much for your reply!  I tried getting the answer to your questions, here goes.  Please let me know whether you think I need to vent somehow or a fan/heater will be fine.  Even your best guess is fine considering I know very little about the subject.

What kind of insulation, and how thick?
R-13 3.5in thick.

Do the lights have insulation behind them in the ceiling?..or is there an air space? ( This is my WAG)
There is an electric box for the wires of the light, behind that there is insulation.

Do the lights give off any heat?
LED lights so not much heat, but there is some.

Is there tar paper, or ice and water under the shingles?
I think tar paper.  They are owens corning roof with lifetime warranty if that helps anything.

How long ago was the sheetrock, and tapping finished?
3 months. 

How big was the temperature difference? 
About 30 degrees F.

Even your best guess on what to do is fine considering I know very little about the subject.  Thanks so much.


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## slownsteady (Jan 29, 2015)

Considering the size of the building, You would prob be ok with a fan/heater. Maybe a dehumidifier. I would guess the moisture is from a lack of airspace above the drywall ceiling, so that is why one guy told you to vent it. You should, if you want the best solution, but it will require more labor. Can you determine if the insulation is wet?


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## nealtw (Jan 29, 2015)

This is a shed built on the problem concrete. Lay a sq ft of poly on the floor for 24 hrs and that will tell you how much moisture is coming from there.
Warm moist air will loose water with a temp change of 30 degrees, and it will condence on the coldest surfaces, vent might help but where to put it would be the next question.


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## alanrudy (Jan 29, 2015)

Slownsteady, I tried, but couldn't determine if insulation was wet or not.  Sounds like you're correct though because there is no airspace between drywall ceiling because wanted to maximize height of interior building.  What/how do you think would be the best way to vent it?  Gable?

Nealtw,  The shed has a 6inch steel foundation so it's concrete, steel, shed.  Where do you think to vent it?  Does poly= polyethylene plastic?


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## nealtw (Jan 29, 2015)

In a house that is heated we want air flow from the soffet to the ridge mostly in cold zones to prevent ice damming. In an unheated building you should not have a problem. The paint on the drywall is somewhat a vapour barrier but there is less insulation around the light boxes so it would likely be the first spot to cool off causing the condenstion. I would think something like a dryer vent in each gable would be enough venting.

Yes poly= sheet plastic of some kind. If the ground below the floor is wet and cool, moisture will wick to the surface on a warmer day and evaporate even if the concrete is dry and it could be an ongoing problem. You could seal the concrete.


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## joecaption (Jan 29, 2015)

A ridge vent, or any roof vent would be useless.
You have no air flow from the soffits to the ridge because there's no baffles.
You have no over hang on the roof so no soffit vents.

That steel frame is going to rust out from being in direct contact with concrete.
Waters going to get trapped under it and not dry out, just lifting it enough to slid in some 2" thick patio blocks would work.


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## nealtw (Jan 29, 2015)

joecaption said:


> A ridge vent, or any roof vent would be useless.
> You have no air flow from the soffits to the ridge because there's no baffles.
> You have no over hang on the roof so no soffit vents.
> 
> ...



Hopefully he has some kind of moisture break under it.:hide:


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## alanrudy (Jan 29, 2015)

Thanks all for the replies.  The steel is galvanized so hopefully that will prevent the rust issue.   I'm definitely NOT not an expert so I'm really helped by your guys' advise on what to do because not sure which contractor's advise I should go with.  So far, dryer vent in each gable has been suggested and also there is a chance I'd be fine with a fan/heater.  Any more suggestions/advise is greatly appreciated.


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## nealtw (Jan 29, 2015)

You might want a heater if your in there working, but you don't want a portable running all the time when you are not there. Vents operate for free.


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## nealtw (Jan 29, 2015)

Actually the heater would give you the same effect that you had when the temp dropped. Warm moist air inside and cool or cold outside.


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## alanrudy (Feb 1, 2015)

Very true, heater could cause same thing, but I guess fan could help.  It seemed a dryer vent in both gables was the only vote so I'll go with that since NOT an expert .  Thanks all again for the input!


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## alanrudy (Feb 3, 2015)

Sorry for my lack of knowledge, but one last concern nealtw...Is there a reason you said dryer vents in each gable?  To protect from rain and since it's only a small space?  Would two regular gable vents be fine?


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## nealtw (Feb 3, 2015)

I was looking at size mostly but it shouldn't matter. Some dryer vent are pretty good in weather and and the have a flapper valve that you could rig for open and closing if you ever want a little heat in the shed.


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## alanrudy (Feb 7, 2015)

So now I've been recommended to add an turbine in addition to the gables?  Think just the gables is okay being 120 sq ft, or I'll really get benefit by adding the turbine?


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## nealtw (Feb 7, 2015)

Overkill.................


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## Big Red (Feb 7, 2015)

You can also buy a powered fan with a thermostat that vents automatically when the ambient reaches a set temp.


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## alanrudy (Feb 9, 2015)

Looks like I'm going to have to nix gable vent idea because it won't solve my issue based on discussion with contractor (he's going to ask around to figure out a solution).  The reason gable vents won't work to solve the problem is because the drywall is flush with the joists, as I mentioned before, to maximize height of interior space, so the gable wouldn't vent that space.  He said there's like 5 pockets that aren't getting vented.  Any more ideas?  Thanks in advance.


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## nealtw (Feb 9, 2015)

Starting over.

No you can't vent the roof sheeting as is with out a lot of time and money.
No you don't need to because this is not a heated space and the insulation is in a closed space.
It was the warm moist air in the shed itself that provided the moisture that condenced on the metal light box and fixture.
Venting in both gables would have allowed the cool air out side to cool the air inside the shed. You still might have condensation lower down, if that happens you would just add a couple more down at the floor level.
This a problem with any shed that has been built tight.  The roof is not a problem unless you heat on when you have snow on the roof.
It's not a big shed so you don't need large vents but you do need to have air circulation.


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## alanrudy (Feb 9, 2015)

Thanks so much for going through it Nealtw, where I got confused is SlownSteady said the problem may be from the lack of airspace above the drywall ceiling (which is true) so I thought that was the area I needed to make an adjustment to.


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## nealtw (Feb 10, 2015)

If you have ever been in an old barn half the time you can see right thru the wall with all the cracks, they get wet and dry out no problem all they had was airflow to help and they last for ever.
Just don't heat your shed when there is snow on the roof.


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## alanrudy (Feb 10, 2015)

It's a bit different since it's insulated/drywalled and want interior like a house, but I get what you are saying about needing airflow.  No snow, just think morning dew and no roof ventilation could cause issue even with gable vents.  Again, not very knowledgeable in this though.


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## slownsteady (Feb 10, 2015)

I'm coming back around to a dehumidifier set on a timer.


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## nealtw (Feb 10, 2015)

What causes a problem with the roof is first warm moist air gets in there that can't get out, can air get into the roof cavities in your roof?
The other problem is when you heat the building, heat willl transfer from the top of the wall to the roof and melts the snow which re-feezes lower down the roof which stops the next melt from running off and then you have a leak.
http://www.luxurymetals.com/freshairintake.html
You can find these cheaper, maybe just one gable and one close to the floor on the other end of the shed.


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## alanrudy (Feb 10, 2015)

No snow where I am.  Re air:  A little amount of air does get through drywall/insulation by way of the hole for the 2 lights (shown in previous picture), it is very small when light is covering up hole.  I do have a window that provides a 17" opening for shed and will keep it open as much as possible.  I apologize for not disclosing I had a window previously if that changes advice, thought my issue was just finding a way to ventilate roof.


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## nealtw (Feb 10, 2015)

The only fix he will come with is remove the ceiling drywall add depth the rafters and a ridge vent and soffet vent and replace drywall. Non of which will solve the problem.
After he give you some idea what he wants to do, send him a link to this site and have him explain it me.


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## alanrudy (Feb 10, 2015)

Okay, yeah I was doing some online research now and eave or soffit vent was recommended as well as air space baffles (don't know how'd that fit).  I will update what is recommended and again, can't thank you enough for helping on this.


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## alanrudy (Feb 10, 2015)

Hi nealtw and others, solution from contractor was to take the ridge cap off, cut 1 1/2" off each side and cover with ridge vent and new ridge cap.  Thoughts?


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## nealtw (Feb 10, 2015)

That is nuts, and what does he say that will fix?


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## alanrudy (Feb 11, 2015)

Really?  It was one of the only ways left he could think of to vent the roof.


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## nealtw (Feb 11, 2015)

Well that would be great if you had a problem with the roof. 
A problem with the roof will come up just like a house. Heat from inside a house gets to the outside wall and over time will travel to the surface of the roof, melts the snow and causes an ice dam which causes water to back up into the shingles and leaks into the house. The other problem is warm moist air leaking into the attic space and not finding it's way out. You have built a closed system attic.
No air in no air out, the paint on the drywall is acting as a vapour barrier, there maybe some small holes here and there and a light fixture. As it is now any moisture that was in the roof area when it is was built is what you there now or maybe less.

So lets look at what happens. When you have hot weather the roof will get hot first and the pressure up there caused be the heat will be pushing warm air out. As the rest of the shed warms up any moisture laying around will evaporate and now you have warm moist air in the shed.
Now what happened that caused a problem is a huge temp change in short time and your insulated shed held on to the heat longer than the surface of the roof. The air in the attic cavities condenced and tried to suck air in to fill the space. As warmer moist air tried to squeeze in past the light fixture it was carrying more more than it could will it was cooling and just dropped the moisture off at the nearest cool area. If the shed cools at the same rate as the roof problem solved.
If I had built your shed, it would have had 2x6 rafters with vents at the soffet and at the peak with four inch insulation so you had air flow beacouse that's what we do but there are argurements for a closed system like you have.
You would also have vents of some kind in the shed itself as even if you were using this as an office or living space you need air. because you use it and you give off lot's of moisture.
If you contractor new anything at all, all this would have been dealt with when the shed was built. 

A ridge vent will only make things worse as now the inside air will find a good path out when you have a big temp change and that will cause rot.


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## alanrudy (Feb 11, 2015)

Thanks for your reply.  I apologize but honestly still a bit confused on why a ridge vent wouldn't help because you described one of the problems of the current closed system is warm air not finding it's way out of attic, wouldn't the ridge vent solve that?
It doesn't snow where I live.  I can leave my window open as much as possible to have air flow.


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## oldognewtrick (Feb 11, 2015)

alanrudy said:


> Thanks for your reply.  I apologize but honestly still a bit confused on why a ridge vent wouldn't help because you described one of the problems of the current closed system is warm air not finding it's way out of attic, wouldn't the ridge vent solve that?
> It doesn't snow where I live.  I can leave my window open as much as possible to have air flow.



Ridge vent only works to exhaust air. You have to install intake ventilation along the eaves to allow for air intake so you can exchange air in the area. 

Think of it this way, I want you to breathe out until I tell you to stop, don't take a breath till I tell you to......still breathing out? I didn't say stop yet.....


Nope not yet.......



Ok, breath, the area breaths by air in and air out and it doesn't happen through the same vent.


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## alanrudy (Feb 11, 2015)

Thanks oldognewtrick, so would a ridge vent AND eave vents solve my issues.  Pardon my inexperience, but sounds like nealtw is saying gable vents are the only thing I can do short of opening drywall and starting over.


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## alanrudy (Feb 14, 2015)

So the conclusion I've reached for now is to do nothing (which is better than $ wasted on contractor ideas that were not helpful) but keep the window open (17"x33" opening) as much as possible.  Based on So Cal weather, hopefully won't have an issue 90% of the time, and during the other time I may get a portable heater/ac or maybe one dryer vent.  Thanks again all for input, and feel free to add anything.


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## nealtw (Feb 14, 2015)

I would think a small vent would be better as with out an overhang an open window in the rain.
This will only happen when you have a sharp down in temp, how often is that?


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## alanrudy (Feb 14, 2015)

Usually at most a couple weeks of rain a year but very good point, may add vent.  For weather, usually at most a couple weeks to a month a year would be the danger zone where nights sometimes hit 40's and the days can get 70's.
Would you recommend to try to seal/cover any holes of the 2 electric boxes for the LED lights to make it more of an airtight/hot roof so it hopefully can't get cold enough for condensation?


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## nealtw (Feb 15, 2015)

Not sure how you would seal the lights now.


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## alanrudy (Feb 16, 2015)

Small gap around both electric blue boxes.  Also, hole for wires could be filled to make smaller.  Good improvements?


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## Perry525 (Feb 17, 2015)

alanrudy said:


> I have a 120sq ft shed/building that insulation and drywall was added flush (instead of flat ceiling) to the ceiling to maximize height inside (please see pictures for hopefully good description).  I had an issue with few drops of water under the lights pictured when I took them off.  First, I thought the roof was leaking but after running a hose on the roof with no leak, the only other thing I'm thinking it could be is condensation.
> 
> Condensation forms when warm wet air meets a cold (below dew point) surface.
> Empty unused building almost never have a problem with condensation.
> ...


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## alanrudy (Feb 18, 2015)

It will be used for a den/office space, but it hasn't been occupied much at all yet even though this issue has already arisen due to the issues nealtw addressed.


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## Perry525 (Feb 19, 2015)

The other side of the story is, warm air holds more moisture than cold air.

Homes and other places that are heated on a part time basis, are subject to condensation when the heating is turned down or off.

Often windows or other surfaces are running in water due to people turning off their heating, or closing their blinds or curtains - during the heating period warm air wafts past the surface keeping it warm (above dew point) when the heating is turned off, or the blinds are closed the air in the recess cools and condensation forms.

This is why it is unusual to have condensation in an unused unheated room, the air holds just enough water vapor for its temperature and the surfaces are at air temperature, therefore, no dew point.


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## bud16415 (Feb 19, 2015)

What&#8217;s the reason for insulating an unheated / uncooled (unconditioned) building?


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## alanrudy (Feb 20, 2015)

I wanted to make the 120sq ft structure as much as a living space/den/office as a home would have so I thought insulation/drywall was the way to go.  I guess the combo of the small space, cold weather, and closed window reeks havoc.


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## bud16415 (Feb 20, 2015)

The reason asked was I started a similar project last fall and your thread has me thinking a little. In my case the room is an addition that was attached to my garage a 14x14 space and I am sealing it all up as I want that to be an all season workshop. I have an air con unit out there and small space heater. But I won&#8217;t be using ether unless I&#8217;m out there working. So most so the time they will be prepped as a conditioned space but not conditioned. In my case I have an outside door but also an inside door to the garage I can leave open to vent the room.


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## alanrudy (Feb 20, 2015)

Yeah, you have a slighter bigger space, I'm not a big fan of ac/heater.  Nealtw's words as well as this link were very helpful in understanding the problem, http://www.etccreations.com/home/cathedralceilings


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