Installing 5V roofing tin

[WV Sawmiller]

   Yeah, I looked at some of the sites and it is hit or miss whether they say install on the peak or on the flat.  I will be using 4/4 rough poplar so the OSB issue is not a factor.

[beenthere]

Shrinking of the yellow poplar drying may be a factor. Don't know. 
Maybe WV will do some exploration for us and monitor any sign of leaking or release of sealing pressure over a few years. 

[WV Sawmiller]

BT.

    Fine with me. I'll put the new roof on my shooting house and 20 years from now we will all meet up here and I'll let you know how it is holding up.

[customsawyer]

I always get the screws that have a little cap, not just a washer. The cap prevents the rubber washer from squirting out if you over tighten it.

[maple flats]

Right or wrong I've heard that on the high ribs is best, but I always put then on the flats, close to a rib. Years ago I roofed my sister and brother in laws barn, 32x66' high hiped roof for more hay storage, using steel roofing  That was about in 1976 or 77. That barn is still dry inside, no leaks. I also did my sugarhouse the same way, on the flats, 22 yrs now and still leak free. I also bought an Amish built building that became my workshop, steel roofing, screws on the flats. I've yet to see any with the screws on the ribs, but i'm sure there must be some.

[Don P]

I've seen homeowners putting screws on the ribs but never seen the instructions showing it. McElroy does still show nails on the ribs of 5v, or with screws on the flats of it and every other profile they offer. Likewise, I've not seen a manufacturer suggesting "venting" the metal, it is always tight to the deck or at least to the tarpaper.

A homeowner does 2 or 3 and never the same, a carpenter does 100, a manufacturer does thousands and hears every callback. That is how I would read my sources.

[moodnacreek]

I would bet the barn leaks so little it is more or less dry. Pitch and exposer to the sun are issues here also. All low screwed roofs of age that I am familiar with leak. None screwed through the highs leak. The fact is that with rib roofing you have rain gutters between the ribs. The only reason to low screw is for wind protection and I think that is why the suppliers say go low. However some have changed their instructions.

[Chuck White]

My house was roofed with steel about 18 years ago and to this day, there's no sign of leaking!

The roofers put the screws on the flats, the only screws on the hump are where the ridge-cap attaches!

Then about 4 years ago I got tired of the constant drip in my garage.  The original roof was nailed directly onto 1x6 furring strips and with any moisture change, condensation occurred and the drip started.
I hired my Amish neighbors to solid board, felt paper, replace the steel and fasten with screws, on the flats, except the ridge cap.

The owner of the building supply store where I got the steel and screws said one of the mistakes that some people make is buying screws that are too short, he said to avoid screws backing out, the screw must go all the way through the wood underneath.

[WV Sawmiller]

Chuck,

    Was your garage sealed tight and insulated? I would bet that would contribute to condensation. My deer stand is wide open with tons of air flow so I'm hoping that helps prevent condensation.

[RetiredTech]

the screw must go all the way through the wood underneath.

I agree they should go all the through, especially on 1X lumber. However I can also verify that doesn't guaranty they won't back out.

[Magicman]

An open shed or non insulated building needs a layer of insulation beneath the metal roofing to prevent condensation and drip.  My open on one side RV shed actually "rains" inside at times.

When my roof is added to my deck to turn it into a porch, it will have a layer of insulation beneath the metal roofing.

 

[WV Sawmiller]

Lynn,

   I've never seen that happen and we had a big pole barn that was at least 48X48 in N. Fla where it was real hot and real humid. It just had 1X6 strips under it IIRC. I've not been having that problem with my 14' X 62' pole barn here in WV. This is the first time I've ever considered putting metal on a solid roof which is why I was asking. 

[Magicman]

The conditions have to be right (wrong) for it to happen and I have never actually made note of what the weather condition was when it was happening.  I will next time.

My builder was insistent that I add the insulation beneath my deck/porch roofing so he was very familiar with it happening.

[Don P]

There's nothing to insulate, that is expensive tarpaper (vapor retarder).

The conditions are the same as the sweaty ice tea glass, the metal (morning temp) is below the dew point of the high humidity morning air. Any exposed surface of the cold metal will condense moisture from the air. Anything that keeps that exposure from happening stops the drip. 

Next tea glass sweating day. Put one glass in the open air in the shade on the porch. Put another in a sealed plastic bag right beside it. Come back in 30 minutes and notice where the condensation happened.

Tarpaper is a high tech solution. Put tarpaper down on a solid deck and it will do all you need. The asphalt coated feltpaper (wood fiber) is moisture vapor permeable when warm and dry. We see it shrink and dry tight when it is dry. When wet it sags and buckles as it swells with moisture. That slams the tar coated fibers together and it becomes watertight. Years ago one of the trade magazines did a test and it did really well at that.

Tarpaper can absorb a small amount of condensation and then release it when the sun shines again. This is known as a "hygric buffer". Wood is one as well, as long as it doesn't absorb too much moisture or for too long. A non leaking roof doesn't approach that level.

I'm surprised the committee has not mentioned how fine it would look with a standing seam roof and then there are no exposed fasteners to worry about  .

[barbender]

This is getting to the level of what oil ratio should I mix my saw gas at?😁

[WV Sawmiller]

  Based on what I am seeing here I am more inclined to just screw the tin to the wood/roof instead of putting strips on top of the roof. That way the wood will serve as insulation. I may break down and put tarpaper or plastic as a vapor barrier between the metal and the wood. 

[TroyC]

When I did my metal roof a few years ago that is what I did. I put down the thick adhesive vapor barrier directly on the plywood then the metal directly on that without furring strips. It is approved by the metal manufacturers. Screws next to the ribs. The thick vapor barrier is also supposed to help with sealing under the screw holes.

[customsawyer]

The roof of my porch and my saw shed will both "rain" when the weather is just right. It is normally when there is a frost. Since I don't get many of those, might explain why us in the south get away with so much. When the frost starts to melt off is when the rain starts. Takes about a hour and it is over.

[WV Sawmiller]

    And if you had much of a breeze I bet it never makes it to raindrop form.

[Chuck White]

In this area, if you look up and see the bottom side of the steel, as weather changes you will get drips!

Put tarpaper, felt paper, or some other vapor barrier between the wood and the steel or it will drip!

FWIW, my garage and house both have ventilation louvers at each end of the gables!  

[WV Sawmiller]

   I ran some errands and stopped by the 84 lumber dealer where I ordered the tin. It ws supposed to be in today. Turned out the order was never received on the supplier end so will be next week. No rush on it. I did look at the 15 lb tarpaper and I guess I will get a roll of it and put a piece under there to that will solve the issue. I'll use the rest of the tar paper under my bee shed which I am also doing a roof replacement. I was going to use strips but now may just put a solid roof on.

[thecfarm]

Maybe I have dumb luck or don't know what I am doing. 
I built a horse run in, 2 big doors in front and I strapped the roof and put the steel to it. Never had it rain inside.

[Don P]

I was making some cornbread tonight. I keep the meal in the freezer. All winter long when I open the freezer door, no fog. The last few days, fog. The rh is climbing. In the winter I can leave the bag on the counter open and not worry between mixing batches. There isn't enough moisture in the air to condense on the meal. This time of year I have to reseal the bag pretty quickly if I don't want moisture collecting on the frozen cornmeal.


A psychrometric chart will fill in the numbers if you want to know when it will sweat. For instance at 75 degrees dry bulb and 58 degrees wet bulb the relative humidity will be 50%. The dew point for those conditions is 50.6 degrees F. If the metal is that temp or below in those conditions, condensation will begin to form.

In my sawshed, which rains frequently, a morning might look more like 60 degrees DB and 90% humidity, foggy mountain morning. The dew point would be 57 degrees, just a 3 degree dawn dip and we're condensing.

Also notice the absolute humidity as temps become more southern. The same RH can hold vastly greater amounts of moisture at higher temps. At 40 degrees F and 90% rh there is 4.7mlb moisture/lb of air. At 80 F and 90% air holds 16.8 mlb/lb

[moodnacreek]

This is getting to the level of what oil ratio should I mix my saw gas at?😁

1/2 pit of 30 wt. non detergent per gallon

[Sod saw]

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Drip Stop is a thin membrane applied (stuck to) the down side of the steel sheets as they are roll formed into your roofing.

That membrane is called felt because it resembles the kind of felt that you use for clothing, not the kind of felt (tar) that folks use for roofing.

It prevents condensation from forming on the bottom of exposed metal roof sheets that may not be screwed directly to a solid deck.

The added cost for this is not as high as it would be if you were to add insulation under that exposed metal.

Up north, here, we also sometimes use Double Bubble.  Double Bubble is on rolls 4 feet or 6 feet wide and 100 feet long and is unrolled on to the purlins of open roof that will receive steel roofing.  Double Bubble is like smaller bubble wrap  that you might use for packing an item for mailing.  It insulates for condensation as well as for cutting down the solar heat that is produced on a sunny day.  Some Double Bubble manufactures add foil to one face of the roll, some don't.

In our wood shed, we have 1 & 1/2 inch of foam sheets stuffed between the 2 x 4 purlins.  Cuts down on the rain and acorn noise while working inside the shed.


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