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Rifraf
Member
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# Posted: 26 Oct 2012 10:04am - Edited by: Rifraf
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Condensation is accuring in my roof area, same as on a window.
I created an air channel in my roof between the insulation and roof sheething. The foam panel on the air channel is getting condensation on it as the house heats. The ceiling is not all finished yet so I have 10 ft on both ends that is just insulation.. If I put my hand between insulation joint near the roof crest I can feel the dew drops on the foam panel that creates the air channel, and the dew is getting on the insulation.
I can also feel air movement from the air channel, im hoping the air movement can keep the dew under control, but i have no clue really.
Is this something that is normal and expected or
should I be concerned? if so , what should I do ?
Comments appreciated.
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PA_Bound
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# Posted: 26 Oct 2012 01:27pm
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If I remember correctly, you have (from top to bottom):
- roof sheating
- air gap (created by foam panel)
- foam panel
- insulation
- what next? (drywall, paneling, something else)
?- For clarity, which side of the foam panel is condensating, the top side next to the air gap, or the bottom next to the insulation? I would expect it to be the bottom side.
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Rifraf
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# Posted: 26 Oct 2012 01:38pm - Edited by: Rifraf
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PA_Bound,
yes you have the order correct.
the final inside layer will be 3/4 inch pine car siding, however right now in the areas im able to reach into and feel the foam, theres nothing over the insulation on in interior side.
The foam panel has condensation on the interior side, I cannot check the air gap side of the foam unless i tear it down..
Whats the prognosis doc ?
EDIT: I just went up and felt in there again, this morning it was dew like droplets here and there and a small membrane of moisture on the foam panel. Now its 1pm and there is no dew drops and it appears most moisture is gone aside from a tiny bit here and there. What does it all mean ?
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CabinBuilder
Admin
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# Posted: 26 Oct 2012 02:12pm
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FYI, similar thread: Will we have a condensation problem?
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PA_Bound
Member
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# Posted: 26 Oct 2012 02:57pm
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Okay... I'm no expert here. But a few items of basic physics to consider.
1. Condensation occurs when something cold is exposed to moist air. How cold, and how moist, determine how much condensation occurs. In your case, the foam layer is very thin so it is going to be to almost the same temperature as the air in the air gap, which will almost be that of the outside air. Summed up, the foam is about the same temperature as the outside air and there isn't much you can do about that (and in fact, that's the way it should be).
2. If we can't change the temperature of the foam, then we need to change the moisture content of the air, or limit how much moist air it actually comes in contact with. How do we do that?
A. Remove as many sources of humidity as you can:
I assume you have an exhaust fan in the bathroom you use when you shower and over the stove when you're boiling water(?). I assume you don't use unvented heating devices(?). I know you don't have a basement so most likley your humidity is coming from daily life activities and therefore tough to reduce- particularly in the winter when your place is buttoned-up tighter. So that leaves Option B.
B. I know you can't add more insulation, or change the type, either of which would be an option here. But how about a tighter vapor barrier in the ceiling, between the car siding and the insulation, to keep the moist air in the cabin from getting through the insulation and contacting the cold foam? Maybe plastic sheeting or something?
Now, even with vapor barrier, if you have too much humidity you may move the problem down to the vapor barrier or car siding. Then the only option I can think of is to reduce the humidity- by reducing the humidty put into the air, exchanging air more often wiht the outside, or mechanical means.
Oh... why the reduced condensation at 1:00? I suspect because the outside temperature increased. Warmer temps=less condensation.
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Rifraf
Member
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# Posted: 26 Oct 2012 03:09pm - Edited by: Rifraf
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If I understand, the best place for this to happen, if its is going to happen .. is there at the foam board so the air channel can help dry it out and move it up through the ridge vent ?
It might not be happening as much in the areas with car siding up, I can only feel test the areas that have not yet got the car siding.
Thanks again!
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Dillio187
Member
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# Posted: 26 Oct 2012 03:18pm
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agreed with above, sounds like you need a vapor barrier + reduction in internal humidity. Are you heating with a vent free propane heat source?
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Rifraf
Member
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# Posted: 26 Oct 2012 03:20pm
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hm,
so do you think it would be helpful or hurtful to poly the ceilings ?
The more I think about it, the more I worry that my humidity levels in such a small space will be hard to keep under control. We have 5 people including my two year old. So we haev several baths a day, even though there is a vent in the bathroom i think thats a major contributor. Then there is the cooking, and we havent even done any laundry in the cabin yet.. we havent purchased a stacked unit.. and while ill have my vents in there im certain it will contribute more humidity..
Perhaps I should invest in a high quality dehumidifier to run in the cold months ?
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PA_Bound
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# Posted: 26 Oct 2012 04:25pm
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My un-professional opinion... it wouldn't hurt to poly the the ceilings- especially if you were already considering that. Anything that prevents the movement of humidity into the insulation has to be a good thing.
How much of your ceiling (car siding) do you already have installed? If you have a bunch, taking it down to install a vapor barrier behind may not be pracitical. In which case I would definitely consider a finish coat on it.
And while I'm thinking about it... do you have a decent Hygrometer (humidity gauge)? It would be interesting to know how humid your indoor air really is. If it's really high, especially in the winter when the outside air is typically lower in humidity, you may want a dehumidifier. If the inside air is low-Normal, a dehumidifier may not help your problem much.
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Rifraf
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# Posted: 26 Oct 2012 06:32pm
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Thanks PA,
ill get a poly coat up when I can.. and I have 12 of 32 feet of the length covered in the wood already. The center 12 feet above the kitchen ! 
I do not have a Hygrometer of any kind, ill look into it. If they are cheap enough ill get one.
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Borrego
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# Posted: 26 Oct 2012 09:41pm
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Do you have eave vents? or roof vents?
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Rob_O
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# Posted: 26 Oct 2012 11:01pm
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You can get a cheap hygrometer but you really need something that can do dew point measurements. Should be something inexpensive available on eBay
An energy recovery ventilator would help with the interior air quality. They start around $400 for a small model
PA_Bound is correct about the interior vapor barrier. You need to dry out the air then seal that dry air between the foam and plastic sheeting. Heat is always going to want to move to cold, and if you have actual air infiltration into the insulation layer that heat is going to bring moisture with it.
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Rifraf
Member
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# Posted: 27 Oct 2012 11:01am
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Borrego, I have ridge vents.
Rob,
So for the vapor barrier you think some felt paper, perhaps #15 , #30 over the insulation, wood planks then poly those?
Thanks
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PA_Bound
Member
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# Posted: 28 Oct 2012 04:45pm
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Rif... I would think that any material impervious to water, and not subject to deterioration over time or breakdown due to attic temperatures, could be a vapor barrier. Is felt paper impervious to water (I'm not certain)? If you use felt paper, make sure you tape the seams to prevent air from leaking through. I was planning to use a decent quality plastic sheeting for mine, but hadn't really thought it all through yet as I'm probably 6 months away from installing ceilings.
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MtnDon
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# Posted: 28 Oct 2012 08:07pm - Edited by: MtnDon
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I believe rifraf is in a hot and humid climate, that also experiences some cold winter weather. If that is correct trying to solve the winter condensation issue with an interior vapor barrier is bound to cause or exacerbate the humidity issues in the hot and humid summer when the A/C is being run. The humid south requires different solutions to humidity issues than the north. Advice that is applicable to northern climates can be the worst thing in the south.
Some of the best information is found on buildingscience.com
http://www.buildingscience.com/search?SearchableText=hot+and+humid
I don't think there is a cheap solution. 
Moisture like that in the roof space will cause issues.
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toyota_mdt_tech
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# Posted: 28 Oct 2012 10:48pm
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Open the ends of the rafter tails (if you have soffits) or cut holes in bird blocks. Then you have to have a ridge vent at the top. The air will move through there keeping it from sweating.
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Rifraf
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# Posted: 29 Oct 2012 08:42am - Edited by: Rifraf
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Thanks,
Toyota, I do have soffit vents, that lead to the ridge vent. The moisture "dew" doesnt last an entire day, its dry by late afternoon.. but pretty wet to the touch in the morning.
MTNDON,
Yea , good memory. I'm in the midwest, and we get both hot humid and cold climate, we are starting our cold now, nights are dropping to the very low 30s, dipping to 29 so far but will be getting colder soon.
would you think that poly on the ceiling would be a good idea then ?
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toyota_mdt_tech
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# Posted: 29 Oct 2012 09:06am
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RifRaf, do you have a rafter system? If so, what size are they? What insulation do you have in between the rafters. You mentioned no soffit, do you have exposed rafter tails? I assume you have bird block vents then?
If you have a 2X6, then you need a 2X4 insulation, ie R13 and have the air gap on the top (just under the roof underlayment. Then you need air to be able to flow all the way through, from the bird blocks out of the ridge. Near the bottom, there is chutes you can install to keep the insulation at the lower part of the rafters from blocking up the bird block vents. They staple in between the rafters.
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Rifraf
Member
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# Posted: 29 Oct 2012 09:38am - Edited by: Rifraf
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Toyota, my rafters are only 2x4s, r13 in them. But will be compressed to about r11 after the car siding is placed because of the air gap I installed in the 2x4 rafters
heres the ridge vent
and eve vents before insulation or anything else went up
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Rifraf
Member
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# Posted: 29 Oct 2012 09:40am
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also here is the air channel 1/4 inch foam as it was going in.
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Rifraf
Member
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# Posted: 29 Oct 2012 10:41am - Edited by: Rifraf
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The other thing im doing at night is running a small space heater.. you dont think this thing it making all that condensation do you ?? Its just a small cheapo electric space heater from wall mart.
The insulation being up without finished ceiling , im guessing is the largest issue I can deal with ? Im also guessing its dead easy for moisture to penetrate that and get up there to condense on the foam ?
Would you guys say my best immediate action should be to finish the ceiling, poly it and get a high capacity dehumidifier for the cabin in the winter ?
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MtnDon
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# Posted: 29 Oct 2012 10:53am
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Quoting: Rifraf would you think that poly on the ceiling would be a good idea then ?
Not exactly.
Why?
First, to restate the layers of the roof, you have shingles and OSB over the air vent space, then rigid foam between the rafters, then fiberglass between the rafters and then the inside finish ceiling material. The moisture you are finding in on the inward / downward facing side of the rigid foam, against the fiberglass insulation.
The moisture condensing on the inside face of the rigid foam is telling us that the foam is cold, below the dew point, not warm enough to prevent condensation. The fact that the condensation is on the inside face tells us the moisture is coming from the inside. As the day progresses the moisture evaporates as the foam warms up. That moisture re-enters the interior atmosphere until the temperature of the foam decreases.
Increasing the ventilation in the air gap will not solve the problem as when it is cold outside that will just make the foam colder, more likely to have moisture condense on it.
Either the foam has to be made warmer on the inward facing side (so condensation will not occur) or the moisture laden air has to be prevented from reaching the cold surface.
A polyethylene sheet vapor barrier can be used to prevent the migration of the moisture laden air through the fiberglass. IF the poly was a perfect install it would keep out the water vapor, however poly vapor barriers are frequently imperfect. In addition if a polyethylene vapor barrier is placed on the inside under the fiberglass that will create a moisture trap between the rigid foam and the poly.
(I believe the rigid foam you used is the extruded type, probably pink or blue. That is a good vapor barrier in itself.)
Add to that, when the weather turns hot and humid again and you have the A/C operating the poly vapor barrier is then on the cold inside. There will be condensation on the cold side of the wall, likely just under the poly. Moisture will be drawn from the humid exterior air. This is assuming the rigid foam panels are an imperfect seal as well.
The real best true solution is probably the installation of more foam. Perhaps the removal of the fiberglass. Like it would have been if spray in foam had been used to fill the rafter cavities. And no venting at all. I am not an expert though; those are simply my thoughts and interpretations of what I understand about insulating and problems encountered in the south. Joseph Lstiburek of the Building Science organization is something of an expert on this. I think I have referenced him and their website a number of times. Good info there with a lot of work done with respect to specific climates.
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Rifraf
Member
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# Posted: 29 Oct 2012 11:08am
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Thanks for the detailed desription.. on this point though.
In addition if a polyethylene vapor barrier is placed on the inside under the fiberglass that will create a moisture trap between the rigid foam and the poly.
sounds like you read me to mean a plastic sheet between the fiberglass insulation and finishing material.. what I meant was a heavy build poly painted onto the wood ceiling material. Do you have any thoughts on that ?
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MtnDon
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# Posted: 29 Oct 2012 11:23am
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Quoting: Rifraf heavy build poly painted onto the wood ceiling material.
There are paints made specifically to act as vapor barriers. They are usually sold as primers. You would still have the potential for moisture getting trapped between the paint barrier and the rigid foam though.
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bobbotron
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# Posted: 29 Oct 2012 12:13pm
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Maybe go un insulated for now?
Maybe you could make a grid of perpendicular 2x6s across those rafters to give you more insulation depth?
Interestingly, I went on a tour of a number of buildings this weekend, that had extensive insulation retrofits. Lots of spray foam used, and blown in cellulose. Near the end I got talking to an insulation contractor, and he said he'd be very hesitant to blow iso insulation against the underside of a metal roof, he said he would be quite worried about dry rot, he said he'd much rather see a air channel put in. Anyway, I'm not saying he is right or wrong, but interesting to think about.
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Rifraf
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# Posted: 29 Oct 2012 01:23pm - Edited by: Rifraf
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unfortunately I cant go uninsulated.. my heat is electric and could not keep up with all the heat loss, I cant just toss in a wood stove either, my kids are not used to one and I just cant afford one either.
I cannot afford to rip out the current system and blow in foam either.. cost is what kept me from doing this to begin with and I was advised on the air channel setup.
I guess i have to decide to finish the ceiling and dehumidify (and hope its enough) or wait until I can afford something else(next summer at best). redoing the ceiling will be very bitter.. i spent a lot of time cutting the soffit vent holes and money on all the materials to add a ridge vent system as well. .. what a confusing and frustrating dilemma, if i finish the ceiling completely and dehumidify I wont have any real way of knowing how successful the setup is
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Rifraf
Member
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# Posted: 29 Oct 2012 09:50pm
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I just noticed today my ceiling fan was going the wrong direction as well, however i'm not sure if this will make much difference
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MtnDon
Member
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# Posted: 29 Oct 2012 10:13pm
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Ceiling fan direction makes no difference in real world practice. We use a fan with unidirectional blades and it works fine summer and winter. It's not even worth worrying about the fan.
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bobbotron
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# Posted: 30 Oct 2012 09:44am
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At least the moisture is condensing on the rigid board, and then drying out there? :/
(Someone correct me if I'm wrong!) The idea with a vapour barrier is to keep moisture from getting to your insulation.. And part of the idea of insulation is to keep the vapour barrier warm, so condensation doesn't form on it. I think if you put a vapour barrier up, since there isn't a lot of insulation there, you'll get condensation on the inside of the vapour barrier. This may be ok in your case, but you might end up with rot issues with the finished interior siding. Or, you might get condensation between the vapour barrier and the rigid board (worst case!) VB polyethylene is cheap, you could put some up and see what happens as an experiment.
It's a tough thing, to not be able to afford more, but in your case, you'll have to accept that less may cost more in the long run. You'll find a good solution, good luck!
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vandersysml
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# Posted: 30 Oct 2012 12:23pm
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Sorry to butt in here, but I'm having a dilemma now that I've seen this post... It looks like Rifraf's cabin is built pretty much the same as mine, same style that is. But I do not have a ridge vent, or soffit vents. I have fiberglass insulation that I was planning on installing this weekend in my ceiling/roof with no venting at all. I'm in Arkansas, so the weather is fairly mild, not super cold conditions like some of ya'll. Am I inviting disaster by insulating this way? What options do I have at this point? The ceiling doesn't really HAVE to be insulated here to be comfortable. Am I better off without it given my perdiciment? I feel like such an amateur for not thinking of condensation.
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