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

dstig1 · Nov 22, 2012

PAGUY said:
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.

I'm sorry, but this is a very bad suggestion. There is no way to foam fill the cavities without distorting the metal. It sounds like a good idea at first, but the foam generates significant pressure, even the low expanding stuff, and it is impossible to fill so precisely as to never touch the tin. It will make the tin look like junk when it all settles down. If you are going this route, you may as well take the tin off and fill the cavities when they are wide open. Then you can control the process. Much easier to just use strips of foam board if you take the tin off which will be a ton cheaper.

There will be no simple solution to this, so you might as well go all the way to get it right. Yes it will be painful, but at least only once.

MotorSeven · Nov 23, 2012

ben2go said:
I too am glad this is coming up now.I have experienced the dreaded tin roof drip.I knew what the problem was and how to solve it.I just didn't know the proper way to do it.I have a question or two about my future set up.Should I ask the question here or start my own thread?

Most of the time posting your own specific thread/problem with garner more responses. Even here on my thread some folks may not read it because it is a general "build thread". Feel free to post anything here you want now that we have the attention of some "drip experts"

Zing, yes that would be a lot of mucking. I am actually thinking about making some side vents on the gable covers at each end of the house that will allow air flow into each of the 5 areas created by the purlins. In addition to more vents on the ridge, this might get air moving enough.

EddieWalker · Nov 23, 2012

MotorSeven said:
Most of the time posting your own specific thread/problem with garner more responses. Even here on my thread some folks may not read it because it is a general "build thread". Feel free to post anything here you want now that we have the attention of some "drip experts"

Zing, yes that would be a lot of mucking. I am actually thinking about making some side vents on the gable covers at each end of the house that will allow air flow into each of the 5 areas created by the purlins. In addition to more vents on the ridge, this might get air moving enough.

I think you're missing the point on how air vents work. It's one of those very simple things that very few seem to understand, especially from reading some of the responses on here. Air flow is created by the temperature change in the air inside the roof. It's warmer in thre then outside. The cool air enters the roof from the lowest vent and then travels up to the highest point. Heat rising is all that you are doing, or want to do. If you ahve side vents, then you are actually defeiting the purpose of creating air flow over and through there.

Air doesn't need a huge volume of space. The ridges on the metal are planty. I wonder how many of the guys on here who are saying they are not, will say the same thing about taping house wrape or around windows becaus of a pinhole gap that air might get through? Air does not need very much space to be effective!!!

The stove is something different. It might creat other moisture issues, but this is simple condensation created by the changing temperatures outside and the buildng retaining a different temperature.

It will be worse throughout the year, and it will go away during parts of the year. It is all about how much moisture, ( percentage of humidity) that is in the air on any given day.

Adding a vapor barrier or plastic sheeting or tar paper under the metal does not stop condensation for forming under the metal, it just hides it and keeps everything dry by carrying the water that forms down the roof and out the eaves of the roof. If you have gutters, you will never see this. If you don't, you will see dripping at the ends of the metal, but probably not realize what side of the metal its coming from. Probably both!!!

Put a vent at the bottom and at the top and see what happens. Don't tear anything apart, don't change anything else. Do it one step at at time and see what happens.

Eddie

Dr Dave · Nov 23, 2012

I agree with Eddie, heat rises, and creates a natural airflow from the eve vent to the ridge vent. By introducing air from the side you will lessen airflow at the eve, the eve area will tend to be your problem area, due to lower temp.

Do you have eve and ridge vents? If not start there first, this is a must have on any heated space,tin or shingles! Midwest Manufacturing has ridge and eve vents, they match the contour of your roof panel, the ridge cap is flat and not formed to the tin. I am not sure how yours is, do you have a good pic of you ridge and eve, if not that may help explain your situation?

Dave

bindian · Nov 23, 2012

ben2go said:
I too am glad this is coming up now.I have experienced the dreaded tin roof drip.I knew what the problem was and how to solve it.I just didn't know the proper way to do it.I have a question or two about my future set up.Should I ask the question here or start my own thread?

Ben,
If you do start your own thread, please post a link to it here.
hugs, Brandi

ben2go · Nov 23, 2012

MotorSeven said:
Most of the time posting your own specific thread/problem with garner more responses. Even here on my thread some folks may not read it because it is a general "build thread". Feel free to post anything here you want now that we have the attention of some "drip experts"

Zing, yes that would be a lot of mucking. I am actually thinking about making some side vents on the gable covers at each end of the house that will allow air flow into each of the 5 areas created by the purlins. In addition to more vents on the ridge, this might get air moving enough.

Thanks.I will post here because it may pertain to your situation.

bindian said:
Ben,
If you do start your own thread, please post a link to it here.
hugs, Brandi

I'm going to post here and when I start my remodel,I'll make my own thread.It will be awhile.

Ok here's the deal.My place will have 16 inch overhangs on the main house with a 4/12 pitch.When I build the decks and add on a utility room,I plan to use lean to/shed style roof of 2/12 pitch.We rarely get snow here.When we do, it's not much.Being that the shed roofs will be directly under the 16 inch overhangs,how would it be vented?I plan to run my perlins across the roof sheathing and tar paper.I know I will stop the roof metal about six inches under the over hangs.When water condensate evaporates,it will go directly up into the soffit vents for the main house roof.I will have baffles running from the soffit vents to the ridge vent on the underside of the roof sheathing.Will this cause a problem with condensation inside the roof of the main house?Oh,all ceilings will be insulated with fiberglass batt and foam board with moister barrier on the warm side.

Rock knocker · Nov 23, 2012

This detail should be applicable to your application:

Venting a shed roof - Fine Homebuilding Question & Answer

Woody65 · Nov 23, 2012

Rick,
I agree with Eddie Walker. I have been a roofer for 28years and have removed many a roof due to poor ventilation. Homeowners would cathedral their ceilings to the roof rafters and not insert baffles between the rafters before insulating. This would cause the sheathing to rot. I would come and take off the roofing and sheathing, install the baffles, new sheathing, roofing, ridge vent and eve vents. No more problem. The baffles are only 12" wide by 1" deep which fit into a 14.5 inch spead between the rafters that are 16 on center. I believe that if you install eve and ridge vents properly, the air will circulate through the cavity via the raised ridges on the metal roofing and, at the least, greatly diminish the condensation issue. My 2 cents from 28yrs of doing roofing in the northeast. Good Luck bro.

dstig1 · Nov 23, 2012

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.