I’ve recently built an addition with a cathedral ceiling. I thought I had done everything right however, I’m starting to get a little bit of water/vapour accumulating on the inside of the vapor barrier (between bottom of insulation vapour barrier) I would also like to add that I live in Canada so it’s very cold in the winter and very hot in the summer. I’ve attached a diagram of what I’ve done. A few other notes the vapor barrier is sealed as I used both acoutical caulking and tape, I know the soffit is clear all the way from the soffit entrace to the ridge. My thought is the water could be caused by 2 issues:
1. The 1/4″ OSB that I used to create the continous vent from soffit to ridge is not an appropriate material and is acting as a kind of vapour barried.
2. The ridge vent that I used does not have enough “draw”, so I should install another model that allows more air flow.
Any help/advice would be very very very much appreciated.
Thanks
Replies
John Smith
Sorry I'll try to clarify a little bit. The water is above the vapor barrier. It looks like it is coming down through the insulation or dripping down the side of the rafters and then running down the vapor barrier. It is not a steady drip about a week ago there was moisture (enough to pool in some areas) in between almost all of the rafter (16" centers). Since then it has been evaporating and there are only a few areas that have any small pool left. However, my fear is that the water is evaporating and then just freezing back up where it came from. I'm worried that I might have a flood on my hands in the spring if I don't address whatever the problem is before then. I also want to add that instead of using those plastic cheap soffit to ridge vent I (based on the recommendation of a contractor) made my own by nailing 1.5" spacers on the side of the rafters and then attaching 1/4" osb to the spacers. The insulation is R40 is under this 1/4Osb vent and the vapor barrier under that.
You may have
a path for warm moist interior air to get past the VB and condense on the OSB insulation baffles. Once it does that it drips back down thru the insulation or along the rafters and that's when you see it. You need to monitor interior RH and make sure you have enough mechanical ventilation.
You may also have a roof leak.
HI David.
I appreciate the quick response. However, I'm almost 100% certain that there is a leak in the roof as it is brand new and was installed in the summer. Shortly after being installed we had a tremendous amount of rain and there was no hint of any moisture. If the cause of the moisture was a roof leak there would have to be approx 30 individual roof leaks as the rafters are 16" centers and are essentially their own little attics. I have been monitoring room humidity over the last couple of weeks and it has stayed very low usually in the 40s (the house is heated by a woodstove). Has anyone here every heard of OSB being used as a baffle/vent? or does anyone have any knowlege of the vapour barrier properties of OSB?
In my above post I mean't to say " I'm almost 100% certain that there is NOT a leak in the roof "
john
There's an edit button on the bottom of the message, you can use that to change words/spelling/etc.
If you add a line or two in the message, you might want to do this (edit) so folks know it has been changed or added to.
For the moisture to be above the osb (and I'm trying to remember if that's the location) it's either a roof leak, blown snow in the ridge vent and melting) or warm moist air getting in the cavities and condensing.
Indoor humidity is not low at "in the 40's". Not high, but moisture laden enough to condense without much air movement.
Any can lights?
Electrical, plumbing, air return or supplies that run up the walls? This might introduce enough of an opening to allow warm air to get in those cavities?
Having seen moisture condense and freeze onto the inside surface of osb in a very cold climate, I can say with certainty that osb will "act" as a vapor barrier at least in the short term. Over the course of a warm summer the osb will probably let the insulation dry out, but that doesn't help you right now. I think it was a mistake to install that 1/4" osb layer as a continuous piece. A layer of hardware cloth would have served you better.
Still, you have a break in the vapor barrier someplace, or everyplace. Is the caulk you used on the VB water tight?
A lot depends on whether the OSB is wax-coated or not. But any of the stuff should be more pervious to moisture than an intact plastic barrier of reasonable thickness, especially since it's probably not well sealed along the edges.
The OP still hasn't given us a clear statement on how much moisture is involved, and where in the assembly it's occurring (high or low or all over). This could be just moisture already in the lumber.
And of course, indoor humidity "in the 40s" is way too high for that far north (if measured at room temperature). Should be under 35 at the highest, this time of year.
correction of sorts
I agree the humidity sounds high. My short but sweet on that is that people like 40% or better while houses like 15%
OSB does serve as a vapour retarder quite well.
The resins that glue all those chips together under heat and pressure is what resists passage of moisture
'course it varies a lot by brand and thickness. cf. this 1/4" osb vs 3/4" Advantech or Huber's Zip system
I'd still love to know just where in the assenbly this barrier is located. Should be up above the insulation but seems to be below it, IMO
I think he's said it several times -- the OSB is between the rafters, spaced 1.5" down from the sheathing. The insulation is below that.
In theory that should be plenty of ventilation, if the ridge and eave vents are clear.
It would be possible (though tedious) to drill holes in the OSB. Slit the plastic, work a piece of pipe in, then drill with a long bit. Probably would work best right at the edges of the rafters, so that one could push the insulation to one side with the pipe. Then angle the pipe slightly to miss the cleats the OSB is screwed to and drill. Work the insulation back into place and tape the plastic.
But if there's only a little condensation (especially given the high inside humidity) then this is probably unnecessary. How much condensation there is is still unclear.
Piffin sorry about the
1. Metal Roof
2. 1X4 Strapping
3. Tar Paper
4. Sheathing
5. 1.5inch airspace
6. 1/4 inch osb used as a vent to keep insulation out of airspace
7. R40 insulation
8. Vapor Barrier
The inside ceiling is not finished yet.
Hi John
Your drawing displays so small for me, that I can't make out the details( even WITH my old man glasses) but it appears as tho you have that vent channel on the wrong side of the assembly.
Here is how I understand what you have from top down...
Metal roof
Tarpaper
sheathing
insulation ( curious what kind? FG batts are famous for being involved in this problem)
The 1/4" osb
A vent channel
The interior finish materials
...
is that right, or am I mis-reading your sketch?
Piffin sorry about the drawing it got compressed with the upload. Heres what was done from the top down.
1. Metal Roof
2. 1X4 Strapping
3. Tar Paper
4. Sheathing
5. 1.5inch airspace
6. 1/4 inch osb used as a vent to keep insulation out of airspace
7. R40 insulation
8. Vapor Barrier
The inside ceiling is not finished yet.
The inside ceiling is not finished yet.
That sir could be one of the up to now unknowns.
Can's?
Taped seams in the vapor barrier?
The warm air on that vapor barrier, the moisture in the framing...........
After Dan implied that I missed something, I re-read the whole thing to put it all together again in my head. He does claim tape and aucoustical caulk sealing the VB well.
If that is the case and this is evenly spread over all 16 spaces, then My elimination comes down to moisture pre-existing in those spaces that has not dried yet, such as wet frame lumber, or possibly moisture blowing in at the ridge vent.
My experience with either of these is that moisture blowing in at top will be more noticeable after a wind+rain and will present itself more near the ridge.
Moisture from condensation will be more noticeable when there is a warming trend after very cold, and will be more noticeable down lower in the assembly and especially on the north side vs warm south side of roof.
OK, I see it now
How tight the inner VB is is a critical element. IF there are no penetrations to it, then it is not possible for moisture to enter the rest of the assembly.
That means tape on seams and caulk around other penetraions.
And adding the actual finished ceiling will retard vapour flow even more.
Since this is a new structure, it is possible that minot moisture can be coming from the framing and insulation itself.
Is the R-40 insulation FG batts, denspak cellulose, hopped FG, or something else?
HI Piffin,
The vapor barrier is sealed very tight with both acoustical caulking and tape. The barrier starts at the floor and wraps the entire room. The insulation used was FB batts. I know that finishing the ceiling will help with moisture however, I just dont want to go through the work and expense of doing so without first being sure that the ceiling is moisture free. I dont want to have to open the ceiling up in 5 years because its leaking or covered in mold. I kind of want to nip this in the butt now.
Can you somehow quantify how much moisture there is, and where it is. Is there enough moisture to run down the plastic (and what is the slope of the ceiling)?
There is enough to run down the vapor barrier. Sorry hard to quantify amounts but between some rafters there is enough to look like it has soaked some smaller areas of the insulation (ie- you could squeeze out water) from about a 3 inch diameter circle. The slope is 4/12. The room is approx 20X20 so there are approx 30 rafters. The starting place of the moisture varies but is generally from a little above half way to the peak and possibly in various places down to the soffit (hard to tell as the moisture obviously runs down).
See my comments to Cal above also
leak in roofassembly
I would check the ridgevent installation.
Heavy rain and wind could drive moisture into your insulation space. With a metal roof the water will slide like on a greased board.
Do not go on a metal roof in this weather without very secure harnessing
Other than the ridgevent there is warm air going into the insulation space somewhere