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

[PAGUY]

Is the answer to this problem running boards vertical under the purlins that are running horizontal before attaching tin roof ? I would imagine a roof ridge vent would help also.

 

[EddieWalker]

Eddie, unless I missed something, there is no real air path from eave to ridge. Just what is inside the ribs of the standing seam you just noted. I don't believe that sufficient area to make a vented roof structure effective, based on the research/codes. It is also not analogous to an air leak at a window flashing as you are dealing with two very different issues. Venting a roof is not the same thing as a leak that can trap water within the walls. You then went on to state what would happen with a proper weather resistive barrier under the roofing - any condensation that forms would drip out and down - true. But if there is no or minimal air space, then this should be down to the level of unnoticeable as there is minimal free air space to put ambient air in contact with the underside of the tin.

And that is the key to an un-vented vs vented roof structure. If you are going un-vented, there must be no air gap. M7's roof has a lot of air gap, it is just isolated from the typical thermal convective loop that forms eave to ridge in a vented structure due to the sleepers being horizontal in his case. Had the sleepers been vertical, all he should need to do would be to vent the ridge and eave, and the roof should be in good shape, assuming the weather resistive barrier (WRB) below the tin is intact. The only point I cannot verify is that the rib air spaces would be any issue, but the cross sectional area seems quite small to be causing an issue. Furthermore, the fact that he is seeing moisture evidence inside indicates that the WRB is either not sufficient or not intact.

Given what I have read and understood, no I do not believe there is a "quick and dirty" solution to this. It is not complicated to fix, but is very labor intensive and potentially costly.

I think where we disagree is in what is enough air to accomplish the task of allowing movement across the bottom of the metal. In my opining, the ridges in the metal are plenty.

You do bring up a point that I hadn't considered. Is there a vapor barrier below the metal and on top of the purlins? If so, this is more then likely what is causing the problem and trapping the air that should be flowing through the ribs of the metal.

Are the ends of the metal at the eaves are open and all he needs to do is add a peak vent?

Eddie

 

[dave1949]

If adding a continuous ridge vent and opening up the eaves somehow to allow air entry fixes the problem, then that would be the least expensive and simplest solution.

Rick would be happy and Eddie could say "I told you so" :laughing: If that doesn't work, then not much has been lost because any other fix will involve removing the tin I think.

 

[dstig1]

Eddie, you could be right, and I don't know the actual "free-air" area of the ribs. It may be enough, I just don't think so from a thumbnail look at it. I should run some calcs to see what it actually is. I'll need to search back for some pics and details in the thread, but can't do that now.

 

[MotorSeven]

We still have company here and had to take 3 young men out shooting today....about 500 rnds of 22LR, 2 Henry's & 2 10-22's= fun. No dripping today and it was a little frosty this AM. Tomorrow AM will be around 20 so we are running both the wood stove and the ventless tonight. Curious to see what we get tomorrow with all this hot air in the house:laughing:

Hey I don't mind the "I told you so's" because that will mean something has been ruled out and progress made!

 

[tony Cecil]

Motor
I looked at alot of roofes today, and I agree with Eddie....I did notice a cap that looked to be about three four inches, rounded, that looked to be made for a tin roof with the V overlaps...Just looked to me to lay right on top of the eve, and probably fastened down with screws...Nothing at all fancy, ant the ends looked like they were cut back in a way that made it look like a little overhand and then the open part that moved the air out at both ends....Nothing big...and looked fine to my eye....Tony

 

[Obed]

Installing a ridge vent and eave vents would be my approach. Then analyze the results. Removing the tin would be a last resort if it were my house. I'd also probably ditch the ventless heater if it turns out to be a major contributor to the condensation problem.

If a ridge vent and eave vents don't work, I might try installing five electric fans to blow air through the tin horizontally (parallel to the purlins) and exit out the sides of the roof. Installing fans would be a lot easier than removing the tin and has a good chance of being effective. The fans could even be set to automatically run when outdoor temps are below a certain temperature.

Obed

 

[EddieWalker]

Just thinking about this and looking at my roof. Are the ends of your R panels sealed? Air should be able to get up under the metal through the ridges and flow to the peak. This should be more then plenty air flow to solve your problems, but if the ends are sealed, then nothing is flowing. Same thing if they ends are open, but the peak is sealed. Open the peak and the air will flow.

Eddie

 

[EddieWalker]

Just thinking about this and looking at my roof. Are the ends of your R panels sealed? Air should be able to get up under the metal through the ridges and flow to the peak. This should be more then plenty air flow to solve your problems, but if the ends are sealed, then nothing is flowing. Same thing if they ends are open, but the peak is sealed. Open the peak and the air will flow.

Eddie

 

[Dr Dave]

Menards has a manual called Heplful Hints for resiential steel roofing, (free) it has illistrations of proper venting and trim installation. Lists part numbers for Midwest Manufacturing products. If you have a Menards near you this may be helpful or maybe they can mail one to you. If not pm me your address and I could mail this one to you.

Dave