Installing 5V roofing tin

[WV Sawmiller]

Question - can you install 5V roofing directly to a solid wood roof or do you need air flow under it?

   I am going to be replacing a roof on my upper shooting house. It is a 6' square elevated building with an 8' square badly leafing shingle roof. I have ordered 4 sheets of 8' 5V tin to replace the roof. I plan to tear off the existing roof and put a solid roof on of 4/4 rough poplar lumber. Because of the distance and slope I have to carry the wood and metal I opted for 5V tin instead of wider sheets I use most of the time.

   In the past I always put metal roofs on wooden nailer strips and they were open underneath. If I need the air flow I can either add some 1X4 strips on top of the roof or just use 2X4s every couple of feet between the 4/4.

   Any experienced recommendations will be appreciated.

   

[beenthere]

Without the air flow, how will you deal with the condensation ? Or will 5V not have condensation from the changing temps??

[Magicman]

Yes it will drip (condensation) inside because of the temperature difference.  It will be minimal but it will still happen.  There is a thin layer of insulating material that you can lay that is shiny in the top and whatever underneath that will prevent this.  You can lay felt between which is not as good but better than nothing.

I am saying what you should do and I did nothing.  It drips, but it ain't much and I ain't changing it.

[moodnacreek]

Put any rough 1" boards close and black paper. Screw through the highs always. All my low screwed roofs leak after 15 years or so and walking on them is not fun with the purlin boards 2' on center.

[Larry]

Thirty years ago I built a house and had true standing seam installed. It is similar to 5V except for the width of the panels. The roof was osb with a layer of heavy roofing felt than the tin. I sold the house but the roof is still in place. I never had one problem with it and still looks good today. Probably the best roof I've ever had.

With standard roofing on out buildings I have went to 1/4" fanfold insulation under the tin. This stops any condensation and cuts the summertime heat a lot. I used a Dow product mostly, but think it is discontinued now. This looks like the same stuff. fanfold insulation

[Magicman]

Screw through the highs always. All my low screwed roofs leak after 15 years or so

My experience and recommendation is the exact opposite.  Maybe it's the glaciated stuff up North??

[Don P]

Where does the condensation come from?

[WV Sawmiller]

    Sorry Lynn but I'm with Moody on this one. I was always taught to nail into the peaks although I see lots of folks nail into the flats. When the washers deteriorate in a few years (I guess there are no more lead head nails like we used when I was a kid) the nail hole will leak.

    I usually tap the peak with my hammer to make a small flat dimple and put my screw there and screw it through. If/When the rubber washer deteriorates the screw is still on a peak and the water is shed to either side and cannot pass through the hole.

  I've been considering whether to put tarpaper down on the roof then nailers on top of that with the 5V on top of and nailed through the nailers but I'm planning on using green stock lumber and it is going to shrink and would tear holes in the tarpaper. Also I only have an 8' square roof (64  square feet) and the tarpaper only comes in rolls that cover about 400 square feet.

  I think I'll put the roof on then nail nailers to that then the metal which will give a 1"  gap for air flow between the metal and wood. I know it will condense some but should not be enough to rot the wood out during my lifetime.

  There is a very good chance I will put the materials on top then finish that and have to shinny down a slender beech tree next to my landing. I keep thinking of Tom's video of Inga and Bill on their  "Elevator trees" .

  When I think of that option I keep remembering a coon hunting trip trip Labor Day night in 1976 just before I left for the USMC. My dogs had treed up a slender tree and left after other coons. We determined it was a baby coon and my buddy said "Let's catch him" which means "You climb up in the tree and grab him while I stay below and watch". (He is now the VP of a Bank/Credit Union so you can see where this is going.) I climbed up the tree till it was about an inch in diameter and leaned on a big Cypress too big for me to climb and the coon was at the tip and about the change trees so I yelled at my buddy I was going to shake him out and to grab him when he hit. I shook, the coon fell past me but without the support of the cypress  my tree bent sharply and quickly and I tried to shinny down till "CRACK" the tree (and Me) fell out in the middle of the  mud and cypress knees and the dogs who had returned. My buddy was chasing the coon but his light fell apart. I stood up in the pitch dark and leaned against the cypress tree for support and when I did I felt fur and grabbed it and caught the baby coon who was trying to escape again. He then squalled and I had all the dogs trying to climb up me, I finally got them kicked back, my buddy got his light back together, I took off my knee high rubber boots and took off a sock to roll the coon it (Socks and shirt sleeves make good catch bags if you don't have a corn sack) and we headed out.

  All was well for about 100 yards till I stepped on something that was whacking my leg and I looked down and found I was standing on about a 36" cottonmouth who was striking my R leg. The only thing that saved me was my floppy boot tops. He was hitting them but did not penetrate my leg.  I set a new state record standing high jump, came down and got my 10/22 Ruger rifle unslung and proceeded to empty the clip till the snake expired then we continued our hunt.

  I don't need that kind of excitement at this stage of my life.

Where does the condensation come from?

The metal gets hot then cools and it gets moist on the bottom. I had the same thing with dripping copper water pipes in my basement till I wrapped them with foam insulation.

[SawyerTed]

Got any unused asphalt shingles?   Throw a layer on before the metal, aggregate side down. Put the metal on.  

You won't ever have to worry about the roof again.  Condensation shouldn't be an issue.  The shingles don't even have to lap like a regular roof.  

[Magicman]

Sorry Lynn but I'm with Moody on this one.

No argument from me nor any reason to apologize.   

When we put tin down with nails we nailed through the peaks.  With the captured neoprene screws, I know of no professional roofer that does not screw through the flats.  If the lath is 1X4's they use 3/4" screws.  If the lath is 2X4's they use 1 1/2" screws. 

[Old Greenhorn]

.......................

  When I think of that option I keep remembering a coon hunting trip trip Labor Day night in 1976 just before I left for the USMC. My dogs had treed up a slender tree and left after other coons. We determined it was a baby coon and my buddy said "Let's catch him" which means "You climb up in the tree and grab him while I stay below and watch". (He is now the VP of a Bank/Credit Union so you can see where this is going.) I climbed up the tree till it was about an inch in diameter and leaned on a big Cypress too big for me to climb and the coon was at the tip and about the change trees so I yelled at my buddy I was going to shake him out and to grab him when he hit. I shook, the coon fell past me but without the support of the cypress  my tree bent sharply and quickly and I tried to shinny down till "CRACK" the tree (and Me) fell out in the middle of the  mud and cypress knees and the dogs who had returned. My buddy was chasing the coon but his light fell apart. I stood up in the pitch dark and leaned against the cypress tree for support and when I did I felt fur and grabbed it and caught the baby coon who was trying to escape again. He then squalled and I had all the dogs trying to climb up me, I finally got them kicked back, my buddy got his light back together, I took off my knee high rubber boots and took off a sock to roll the coon it (Socks and shirt sleeves make good catch bags if you don't have a corn sack) and we headed out.

........................

 

All I could hear in my head when I read this was "Knock him out JOHNNNN!"

[WV Sawmiller]

Ted,

   I have 3 bundles of asphalt shingles I bought at a bargain at a local flea market. If you want to volunteer to lug them up that steep slope for me I will be glad to use them.  

   I get a back ache just thinking about carrying them up there.

Tom,

   In my prime I'd have given John Eubankls a serious run for his money when it came to tree climbing. 

    I well remember climbing a big magnolia in the swamp behind my house with this same buddy along one day while  looking for flying squirrels. About 50' up I stepped on a big dead limb that broke and must have weighed 40 lbs. I was up there hanging by one arm watching the limb headed straight for my buddy below knowing it was fixing to kill him. At the very last second he stepped back one step and it hit about 6" in front of his toes. 

[Don P]

Here's where my mind goes, which I think will line up with the manufacturer specs, which is what you should be reading. I think they want 5v on a solid deck but either way moisture comes from the air in contact with metal that is below dew point
 
Why in the world would someone then say, let me pass more saturated air on the underside of said cold metal. That would cause sweat on the underside, which would then drip down.

Put the underside in direct contact with solid decking covered by tarpaper. First, there is no saturated air hitting the underside, no condensation. Any minor water is absorbed by the paper till the sun shines again, then vapor drive follows heat drive, the moisture is pushed to the underside on the sheathing where the ventilation should flow... if there is insulation this is its air channel under the sheathing as well.

[moodnacreek]

Screw through the highs always. All my low screwed roofs leak after 15 years or so

My experience and recommendation is the exact opposite.  Maybe it's the glaciated stuff up North??

My experience comes from several roofs on the barns and several here at the sawmill plus many others done by my son and customers. Over time the screws work up and cause a small leak and rot a little around the screw so you need a thicker screw. The damage done to the items stored like lumber; stained and full of ppb was or is completely unnecessary. This mistake has really cost me and it is not over yet.

[WV Sawmiller]

    Sounds similar to my experience. The wind and heat and cold lift the metal and loosen it. Being over a solid roof on my shooting house should reduce the wind's effect. As mentioned always before I just had the metal attached to nailer/strips and the rest was open.

    One tip I have used and really appreciate that came from Tom King IIRC was to use rivets to repair nail holes such as in used metal or if you miss a nailer. The good thing about the rivet is you can install them from above or below. From below it is easier to spot the light and where you can reach it from below you can seal it.

[SawyerTed]

Ted,

  I have 3 bundles of asphalt shingles I bought at a bargain at a local flea market. If you want to volunteer to lug them up that steep slope for me I will be glad to use them.

  I get a back ache just thinking about carrying them up there.

Piece of cake!  It won't take but 25 shingles edge butted together.

If you can carry the poplar boards, 4 pieces of 24x96 metal roofing and all the tools, 25 shingles ain't nothing! 

Of course I'm just a young man of 61!  Driving to WV will be harder than carrying shingles!  

[Old Greenhorn]

....
Tom,

  In my prime I'd have given John Eubankls a serious run for his money when it came to tree climbing.

    I well remember climbing a big magnolia in the swamp behind my house with this same buddy along one day while  looking for flying squirrels. About 50' up I stepped on a big dead limb that broke and must have weighed 40 lbs. I was up there hanging by one arm watching the limb headed straight for my buddy below knowing it was fixing to kill him. At the very last second he stepped back one step and it hit about 6" in front of his toes.

Just for the other folks not following what Howard and I are referring to in these side comments, because i (we) don't want to be rude, here is the story we are referring to:

[moodnacreek]

I have a recording of that.

[RetiredTech]

Put any rough 1" boards close and black paper. Screw through the highs always. All my low screwed roofs leak after 15 years or so and walking on them is not fun with the purlin boards 2' on center.

I have to disagree with that too. I put the roof on my house in '95. We screwed it through the peaks beind careful not to strip the screws. That was a bad mistake. Within a few years I had screws baking out of the roof. I've had to tighten screws back down several times over the years and I'm always fighting small leaks around the screws. My advice would be to put down some felt or insulation sheet then strip on top of it with 1 by material and screw through the flat being careful not to over tighten the screws. Just tight enough so they start to bulge but not stick out from under the washer.    

[WV Sawmiller]

RT,

   I don't see how you are getting even small leaks if you installed the screws through the peaks?

[RetiredTech]

 Unlike the old lead nails we used to use the screws will back themselves out. I don't know why.   Another problem is years of being screwed down on the ridge the neoprene washer will deform and/or crack. They're made to be installed on the flat. That's a fact I did not know when I installed the roof. My roof has been nothing but trouble. It's a story and a half, I believe it is 6/12. That's been too long ago for me to remember. You can not stand or even sit on it. It's a pain to work on. On the other hand, my shed is a low pitch roof and was installed with the screws in the flat. I've only had two leaks in it. Probably from over tightening the screws. That's just my experience, YMMV. For me I'd never put in another 5v roof screwed through the ridge.

[beenthere]

On the flat or on the ridge.. is a catch 22. They both can and likely will leak at some point in time. 

May just be that there is, and/or will be, some need for maintenance either way. 

[RetiredTech]

On the flat or on the ridge.. is a catch 22. They both can and likely will leak at some point in time.

May just be that there is, and/or will be, some need for maintenance either way.

Agreed. The main reason I went with the 5v on strips was to hear the rain and not to have to replace shingles every 20-30 years. Well, I haven't had to replace a shingle and I still enjoy listening to the rain tinkling on the roof. Life is good! At least until I have to scale the roof again. 

[SawyerTed]

A manufacturer guide specifies 1 1/2" screws on peaks.

Any backing out of screws is probably due to heating and cooling, urethane caulk (can get colors to match roof panels) on the screw prior to installing will usually help screws stay in place if backing out is a problem. I've spent more than an hour or two adding caulk to new screws while refastening a metal roof to stop leaks.  Backing out happens more with OSB sheathing.

The biggest DIY mistake is using an impact driver to drive the screws - they over drive screws/over compress washers.  A screw gun is a better tool. 

But hey, we use what we've got, right?

[RetiredTech]

 That's interesting. I used silicone caulk on the screw threads the last few times I had to work it. I guess anything would be better than nothing. I can't say that I have had to redo any of the screws I've done that way. I also put a small dab around the base of the washer. I still think I'll screw though the flats from now on. Experience tells me it just seals better. I think you are 100% correct on the impact driver. A cordless drill with a properly set clutch is the way to go.

[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]

.


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.


.

[Oliver05262]

A half pint to a gallon —-16:1. That would make my 1-76 McCulloch happy.

[WV Sawmiller]

   I use 1 pint to 6 gallons on everything I run (50:1) - Outboard motor, chainsaw, weedeater

   I got my 5V tin yesterday and a roll of 15pound roofing felt and a couple pieces of drip edge so not just need to haul it up the mountain and make the replacement.