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

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alanrudy

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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’t usually rain) so the difference between the cold ceiling and hot interior created it. I’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’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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Here are some more pictures, could really use advise. Thanks in advance.

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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...:)
 
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.
 
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?
 
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.
 
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?
 
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.
 
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.
 
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.

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.
Click to expand...

Hopefully he has some kind of moisture break under it.:hide:
 
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.
 
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.;)
 
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.
 
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!
 
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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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.
 
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?
 
You can also buy a powered fan with a thermostat that vents automatically when the ambient reaches a set temp.
 
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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