The Log house Project begins........

[PILOON]

If you do go for the ridge vent system be sure that there is a tight seal wherever the vent 'chamber' meets the roofing (also seal the ends) otherwise the ridge vent will attempt to draw air from all those openings and not from under the metal deck.
I know that around here they sell foam fillers that conform to the ridge pattern of the roofing for just that purpose.
A for sure cure would be to add 2x4 to the top of your rafters/trusses and re install on top of that, that way you would have a 3 1/2" air passage from eaves to the top 'vent tunnel (chamber)'.
Don't know if you have Maximum brand vents down there but they have been proven to be the most effective as tested by CMHC* and far out perform any of the rotating type vents that freeze up when humidity gets in there.
The Maximum is like a metal Cupola about 12 x 12, insulated, with screened louvers on all 4 sides. (about $100).

*Cdn. Housing and Mortgage Corp


As to the non vented propane heater, just look at the composition of propane. Water is H20 and propane is something like H22O11 (?), like all moisture!
Also your building is all fresh new wood, not kiln dried #1 stock. A new construction will always have a much higher moisture content until it has a couple of heating seasons under its belt.

 

[PILOON]

If you do go for the ridge vent system be sure that there is a tight seal wherever the vent 'chamber' meets the roofing (also seal the ends) otherwise the ridge vent will attempt to draw air from all those openings and not from under the metal deck.
I know that around here they sell foam fillers that conform to the ridge pattern of the roofing for just that purpose.
A for sure cure would be to add 2x4 to the top of your rafters/trusses and re install on top of that, that way you would have a 3 1/2" air passage from eaves to the top 'vent tunnel (chamber)'.
Don't know if you have Maximum brand vents down there but they have been proven to be the most effective as tested by CMHC* and far out perform any of the rotating type vents that freeze up when humidity gets in there.
The Maximum is like a metal Cupola about 12 x 12, insulated, with screened louvers on all 4 sides. (about $100).

*Cdn. Housing and Mortgage Corp


As to the non vented propane heater, just look at the composition of propane. Water is H20 and propane is something like H22O11 (?), like all moisture!
Also your building is all fresh new wood, not kiln dried #1 stock. A new construction will always have a much higher moisture content until it has a couple of heating seasons under its belt.

Many many chalets in my area were built with cathedral ceilings as occasional usage buildings. Later on folks moved or retired to their chalets and as a result we see many houses sporting 'roofs on top of roofs' in order to increase insulation and add air space.
It looks like you covered the vapor barrier and insulation side of things quite well but just under calculated the need for air movement in your 'attic'.
Good luck, you'll beat it yet.

 

[pacerron]

The attached pdf article may be a little deep but if you read it carefully from start to finish with an open mind you will see that the air flow blockage by the 5 horizontal purlins on each slope are a big factor. You can't believe that a little bump ridge formed vertically at 1 foot intervals is going to evacuate all the moisture under the tin between the bumps. Even air under pressure would not do it, as some would have you think.
Pour some water on your kitchen counter a few inches wide and blow air through a straw in the middle of it and see where the water goes.
Add to that a 1" high barrier beyond the water and see if you can blow the water over it. Now think about doing that up the slope of your roof.
On there the water will have collected against the top edge of the purlins so air going up the bump channels will have little, if any effect.
More water will soak into the wood purlins and create a scum over the styrofoam and likely start mold growing in the spring.
That's about it for me. You've heard all kinds of suggestions and theories but you will have to choose how to fix the problem.
Hope everyone has a happy Thanksgiving.
Ron

 

[Rock knocker]

I hear ya Eddie, this one is going to be a log study.

Ron I did talk to my metal roof supplier today. He is not a roofer, but sells a ton of tin in our county. He agreed more airflow can't hurt, but he also said that this is a common thing that may or may not develop into a bigger problem.

Rock, (1)yes, (2)I'm re-thinking this, no way is water vapor from the house getting to the underside of the tin. 30 weight tar paper & 3" of foam which was all seam taped prior to the purlins going on. (3)maybe but would that not cancel out number 4?

Why are you going to stop using the ventless if there is no way water vapor from the house is getting thru the VP, foam insulation and felt paper? My opinion is based on a life-long career in construction, and I'm just looking at the obvious issues. Condensate and ventless appliances kind of go hand in hand. As do a lack of insulation and condensate, especially in very cold areas. If the people who are acquainted with your area subscribe all the problem to exterior humidity condensing on the underside of your metal roofing, I will accept that. But I would also prescribe remedies which are common in other areas

 

[955Lincoln]

Rick, I'm not a roof guy but I'm reading all of this and picking up clues from the posters.

Air flow:

1) Don't forget about pacerron's uninsulated barn or my overhang. You can't get much better airflow in these cases and there are still problems.
2) You have a good vapor barrier and I can't see how the inside conditions are affecting this problem.
3) Eddie's cold glass (or metal can) of water vs. a styrofoam cup. Moist outside air is going to condense under your roof with the right conditions.

I think if the metal roof industry could go back and start over you would see roofs with insulation tightly adhered to the inside surface. Maybe there is such a product? Anyway, I'm not seeing outside airflow as a solution unless you can control the air moisture or dewpoint which of course is just silly statement but I didn't know how to write it any other way.

 

[dstig1]

Whoa. The little ridges in the tin are not a real concern. A little air will be in there and can condense water, but if it has a way out at the bottom (at worst) it will not be an issue.

The issue AGAIN is one of two paths:
1. Insulation right under the tin, and have it sealed for water tight use. No air, no condensation.
2. Vent space under the tin. This is covered well by Eddie - vertical (eave to ridge spacers), plus vent spaces at BOTH the eave and ridge.

Realize that both are acceptable, as long as they are done properly.

 

[DougM]

Snice the metal Roofing is in stalled would it be possible to place 5 small fans on the edge of the roof creating air movement side ways ??/

 

[PAGUY]

I think Eddie is right in his opinion that you hire a foam insulator to fill in the gap between tin and sheeting. It would not have to be filled tightly but enough so lack of all that air space that you have now because of purlins.

 

[MarkV]

Rick you might give this forum by the Metal Roofing Alliance a try with your roof problem. Condensation Issues: Page 1 | Metal Roofing Forum

MarkV

 

[GLyford]

If the moisture from the ventless was condensing on your vapor barrier, where would it flow to and show up coming out of the house? Would it end up in the same spot? Is there any way to take off a piece of eave trim and find out if the water is coming from over (roof) or under (ventless) that vapor barrier?