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

[EddieWalker]

Pacer has a grasp of it pretty good:
"The problem is they are not reading or understanding your roof layers where you have the horizontal purlins blocking air flow from the eaves to the ridge every couple feet or less and creating water dams at each purlin."

However there is an vertical air pathway(raised rib) built into the tin sheets every 12" and that same rib creates a 'vent" of sorts at the ridge cap. Maybe by putting in a more or proper vented cap I can get more air movement and that would be the least expensive & least labor intensive attempt to remedy this.

Eddie is spot on ref the nature of condensation and it's inherent issues. Hindsight says I should have at least put a vapor barrier on top of the purlins but I have never seen this done. Not so convinced that foam adhered to the tin will even stop condensation. The quonset has 2" of sprayed foam directly on the metal and water will even drip off the foam during certain weather conditions.

Yesterday I had more water dripping, but about half the amount of the day before. It looks like weather conditions will affect this quite a bit. I appreciate all the ideas...keep 'em coming while I monitor the "drip":thumbsup:

I don't believe that a vapor barrier would accomplish anything on your roof other then hold water in there to grow mold and cause other issues. I've seen this happen before and it's a mess.

Condensation is caused from the different temperatures on either side of the metal, at the surface of the change. By adding a thin layer of foam, you create a temperature barrier that will eliminate most of it. Glass of ice water compared to a styrofoam cup of water type of thing.

Since your rafters and purlins overlap each other, adding vents would be the first step. Bigger is going to be better since you need to have as much air flow through there as possible. As long as the air can get through the openings, venting will help.

Eddie

 

[955Lincoln]

I'm not sure if this will help in any way. This overhang has a simple metal roof over open rafters and I get lots of rain under it. I haven't paid much attention to the conditions but I have noticed that sometimes there is frost on the underside of the roof. The overhang is pointing east and as soon as the sun peeks over the mountain the rains begin.

 

[pacerron]

Pacer has a grasp of it pretty good:
"The problem is they are not reading or understanding your roof layers where you have the horizontal purlins blocking air flow from the eaves to the ridge every couple feet or less and creating water dams at each purlin."

However there is an vertical air pathway(raised rib) built into the tin sheets every 12" and that same rib creates a 'vent" of sorts at the ridge cap. Maybe by putting in a more or proper vented cap I can get more air movement and that would be the least expensive & least labor intensive attempt to remedy this.

Eddie is spot on ref the nature of condensation and it's inherent issues. Hindsight says I should have at least put a vapor barrier on top of the purlins but I have never seen this done. Not so convinced that foam adhered to the tin will even stop condensation. The quonset has 2" of sprayed foam directly on the metal and water will even drip off the foam during certain weather conditions.

Yesterday I had more water dripping, but about half the amount of the day before. It looks like weather conditions will affect this quite a bit. I appreciate all the ideas...keep 'em coming while I monitor the "drip":thumbsup:

Rick,
You have already experienced the fact that the little ridge bumps in the roof tin every 12 inches won't get rid of the moisture.
My wife who is at the horse shelter numerous times per day says whenever there is frost on top of the roof, there is frost on the underside. When it starts to melt it rains inside the shelter as I mentioned yesterday. I took some pictures of the difference from insulated versus uninsulated this morning here. The big barn is insulated and you can see a tiny bit of the uninsulated open side of the horse shelter behind it. They both have vented overhangs and vented ridges.
The roof insulated above the purlins in the big barn creates a dry environment in there regardless of the weather.
Another thing I would be concerned about on your house is the potential ice and snow build up in the winter at the gutters and on the slope above the overhangs leaking back in when the snow and ice melt. We finally got our house roof replaced from the storm back in June and it is now required to have the first row of underlayment around all edges to be the expensive rubber material with mastic on the back. Same thing in any valleys. And that is on a 10/12 slope.
Mold under your roof could be another concern, as Eddie pointed out.
I don't know what kind of finish you have on the underside of the roofing but where it may be scratches, have a sheared end, or where nails or screws go through it; sooner or later will rust. Then you may have rusty gooey water coming out staining everything it touches.
You can see in my pictures of the horse shelter under the roof how the trusses have weathered from the moisture and open wall. The lumber in the big barn looks like it just came off the truck; but 20 years have transpired on both buildings.

I would still get some advice from some commercial roofers before jumping into anything.
I really agree with ENG 18 LT above that the only good solution is to take the roofing off and do it right.
Ron

 

[MotorSeven]

Thanks for the info from all of you. There was even less "drip" today because the weather was a bit warmer. Foam might be the answer, but getting it under the roof without removing it is going to be a large project. I think I want to monitor the problem and do a daily log for at least a month before I make a decision. If I have to remove the roof I will do so, but I don't want to rush into anything that will cost a bunch of $ $& time.

 

[MotorSeven]

Pacer, you have zero insulation there...I have to wonder how much effect on all this insulation has?

 

[pacerron]

Pacer, you have zero insulation there...I have to wonder how much effect on all this insulation has?

Rick,
Not quite sure what you are referring too?
1. The little 24 x 36 horse shelter has zero insulation. The last 2 shots are showing the underside of that roof. That's the one that rains. Same as in your case the underside of your tin has an air space that gets frost on it and lays along the top edge of your purlins when it melts before leaking out someplace.
2. Pictures 4 and 5 show the underside of the 64 x 84 barn roof.
The aluminum color you see between, actually above the purlins, is the bottom of the insulation board. The bottom of the roof tin is in contact with the top of the insulation board. So the only air space is under the bumps. Since there is no trim over the bumps at the spouting end any moisture in the bumps can flow unrestricted to the spouting. Normally, unless blocked by a snow or ice dam, air flows up through the raised bumps and exits at the ridge vent which runs the entire length of all barn roofs.
In the horse barn, that has no insulation, you can see the open groove in the picture at the ridge that lets heat and air flow up and out on the inside of the barn.
The big barn has no ridge groove. The insulation makes a tight seal up there.
There is some cross flow venting on the gable ends because of the purlins being above the trusses. It is covered by metal trim on the outside similar to what you show on the end of your house.
With the roof being so high and insulated, it is always cool in there up to the bottom of the trusses in the heat of summer.
Good luck on your problem.
Ron

 

[Ranger Rick]

The big barn is insulated and you can see a tiny bit of the uninsulated open side of the horse shelter behind it. They both have vented overhangs and vented ridges.
The roof insulated above the purlins in the big barn creates a dry environment in there regardless of the weather.
Ron

Ron, How much insulation above the purlins do you have in your big barn. I am about ready to put a metal roof on a pole building shop that I am building and the condensation issue is a real concern for me too. I would like to prevent the problem from happening in my building. Rick

 

[dstig1]

If i understand the setup correctly, the solution would be something like this
1. 2" foam over decking. Seal seams with tape and/or add weather resistive barrier on top (something like 30# felt, or a synth roofing cover. )
2. Either lay the metal roofing directly on this, or space with vertical strapping (running eave to ridge) min 3/4" thick. Include vent space at eave and ridge.

The key is the vapor barrier above the foam so any condensation stays outside. If you put the metal directly on the foam, there should be minimal condensation to deal with as there is no air space. If there is air space you must vent it!

Bad deal is that I think you will need to strip the roof and redo it next spring ....

 

[pacerron]

Ron, How much insulation above the purlins do you have in your big barn. I am about ready to put a metal roof on a pole building shop that I am building and the condensation issue is a real concern for me too. I would like to prevent the problem from happening in my building. Rick

I don't remember the thickness but it was an inch or less. It was a rigid material covered on both sides with foil. The foil was more important than the thickness to control heat or cold radiation from the outside and to be reflective from the inside.
I had a crew of Mennonite barn builders do the construction 20 years ago so the thickness evades my memory.
Newer technology materials are available today but I am perfectly satisfied with what I have. We don't heat the big barn.
Since you are going to use yours for a shop you may have additional requirements.
Ron

 

[PILOON]

I have done a few metal roofs on homes so can offer some opinions and observations.

The problem arises from moist air condensing on the underside of the metal.
Tightly sealed vapor barrier is very critical and more so than on a shingle roof.
Moving out that moist air will greatly help cure the problem. One home I worked on (8 ft attic) condensed so badly that the ceiling sagged from the dripping condensation.
A substantial ridge vent will greatly help (and not the devices supplied by metal roof vendors).Make one up similar to what they install on sugar shacks. This would be like a second small roof perhaps 2 feet wide straddling the ridge and perhaps 6 ins high. i.e. a ridge tunnel. You would have cut back the roofing somewhat by less than the foot overlap on each side to allow moist air to escape into the 'tunnel'. Next that tunnel needs a chimney to evacuate the accumulated moist air.
Critical also is blocking spaces between the ridge vent and roof deck otherwise the vent will only draw local air and not the air from the eaves that carries all that moisture.

I once removed a tin roof that had been laid over plywood because the lady did not wish to hear the drumming sound of rain.
The (galvanized) tin was so rusted out that you could ball it up like paper and the ply rotted; that was a 10 yr old roof!

Hope I have added some light to the tunnel.