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fcmazz 11-23-2009 09:06 PM

Moisture in Cabin
I have a problem with moisture and maybe someone can help or been there before. I had a cabin built like this one here:

Problem is that I started to put up the sheet rock on the ceiling and I noticed the insulation paper was moist. There are several areas on the same ridge with moisture.

Behind the insulation (OSB), it was not moist but dry. That is confusing and was wondering if I can stop this moisture somehow. Where does the moisture come from? Texas gets hot but why not all the insulation is in the same condition....

I'm not sure if I should continue with the sheet rock on the ceiling; maybe the moisture will stop. We have had rain but the roof has new shingles and don't see where the rain would come in. Besides, I think it would be more than drenched and not just moist if there was a roof leak. Below is another pic of the moist area. Anyone have any ideas on this issue?


MJW 11-23-2009 09:29 PM

Moisture and heat go up, and then it is trapped. You need Poly on the inside sealed and it needs be vented all the way from the eave to the peak with a ridge vent.

Right now, you are treating the ceiling like a wall, and in short, that doesn't work with fiberglass insulation. It needs area to vent the moisture out. The moisture comes from different temps inside and out, and simply just being in the cabin.

Scuba_Dave 11-23-2009 09:38 PM

Yup - you need venting, rafter vent before insulation goes up
Allows heat & moisture to rise & exit the building
Do you have roof vents of any type?
Soffit vents ?

fcmazz 11-24-2009 05:39 AM

Wow- putting up roof vents may stop the moisture. Anyone have pics of roof vents to I can see what we are talking about, where to place them or how many? New at this and appreciate all the feedback and advice I can get. I have no sofit. Just have the shingles on top of the OSB and inside are the joists covered with R19 insulation.

Thank you all for the replys.

Scuba_Dave 11-24-2009 10:36 AM

Roof vents need rafter vents & soffit vents to allow air to circulate & escape

fcmazz 11-24-2009 11:02 AM

This something that can be bought like home depot or lowes? Kind of hard to picture where the insulation goes if the baffle will be in the way. Seems the sheetrock will not be flush?
Again, I'm new at this so just trying to get a vision..


Scuba_Dave 11-24-2009 11:13 AM

Yes, rafter vents can be purchased at HD or Lowes - 16" or 24" widths
They go up 1st, then insulation over them
What size are your rafters ? 2x6 & you are using R19 from what I can see
The rafter vents take up approx an inch of space
Do you need to heat the area or just AC?

fcmazz 11-24-2009 11:24 AM

Now I'm seeing the light. This helps out a bunch. I have 24" rafters 6" inches deep. So guess I would buy the metal baffles or styrofoam like the ones in the pictures? Tried to search HD online but no images available. Does each inbetween space get a baffle?

Scuba_Dave 11-24-2009 11:40 AM

Yes - each rafter space gets one. 1/2-2" space between vents as you staple them up the cavity
They have styrofoam versions & plastic
I buy the plastic version at HD or Lowes - they don't show a lot of what they have online

fcmazz 11-24-2009 11:45 AM

You DA-MAN and I think you just fixed my problem. :thumbup: Heading to lowes after lunch here.

Extremely grateful for your time and responses on this issue.
Thank you again and have a great Thanksgiving.

MJW 11-24-2009 12:46 PM

If you don't have soffit vents it won't work as it is supposed to.

It appears like you will need the baffles all the way to the peak though.

jogr 11-24-2009 04:37 PM

To me it appears the moisture is condensation on the bottom surface of the kraft paper barrier not on the osb. If so, I don't see how the vents will help at all and could cause more condensation if they cool off the inside surface of the paper faster at night. But I am a Northern guy, and maybe that's why it's not clicking.

Up here I would look at it like this- the problem would be too much moisture in the building and/or inadequate ceiling insulation allowing the kraft paper surface to cool off to below the dew point of the inside air (probably at night). A layer of drywall and vapor barrier paint might do the trick if you are right on the edge. This will move the potential condensation point to the exposed surface of the drywall which will probably be slightly warmer than the current surface temp of the kraft paper. In the end though you would probably need lower humidity in the building (bath fans, kitchen fans, HRV etc).

I guess down South you guys actually have problems with humidity driving in from outside and condensing on Air Conditioned surfaces - which is maybe what's happening here. If the condensation is on the top side of the kraft paper instead of the bottom then that makes sense. I guess then the venting will clear out the hot humid air quicker than the surface cools though it almost seems better to have the rafter bay vapor barrier sealed tightly with a vapor barrier on the outside for you Texans so the humid air can't enter to begin with.

Sorry for thinking out loud here, I just find it interesting how different climates cause differrent building issues.

tinner666 11-25-2009 07:34 PM

Don't forget to remove the cap and install continous ridge vent, along with the continous soffit vents. You'll need to make sure the area isn't blocked of where the mansard transists (sp) to the low slope. You might even have to install continous venting along that edge.

This is what you will probably have to do.

oh'mike 11-26-2009 06:20 AM

Tinner--Thanks for the link to the soffit vents--I'll have a use for those!

FC- ScubaDave has you on the right track--Lucky for you that the problem was discovered before the sheet rock went up.----Good luck-have fun--MIKE--

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