# So what is the RIGHT way to  install/insulate metal roofing?



## mikeathens (Jan 21, 2009)

I've heard a million ways to install and insualte metal roofing, but it seems that for every one, some "expert" will tell you to avoid every one.   Here's my scenario:

I'm building an addtion onto my house.  It will replace a flat roof with a 4/12 pitch shed roof, engineered rafters.  The underside will be "cathedral ceiling".  

I had been planning on (from bottom to top) tongue-in-groove ceiling , rafters (16" OC with dense pack in between), OSB, tar paper, and metal roof on top.  Then I read of somone with this same construction method complaining of condensation dripping through on the north side.

So what is the BEST, MOST COST-EFFECTIVE WAY to construct and insulate a metal roof to avoid condensation/dripping on the bottom side?


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## d.n.f. (Jan 21, 2009)

Not sure about the cost but I saw a metal roof install where the roof was like on big sip panel.  Metal roof, 1 foot of foam insulation, and then something on the inside which I didn't see ( I was in the car watching the crane).  The guy said the roof was like r75 or something.  The whole roof for this log home came in two pieces.  Crane lifted them and they got bolted together.  Pretty cool.

I am sure something like that ain't cheap though.


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## mikeathens (Jan 21, 2009)

[quote author="CZARCAR" date="1232585339]i dont get the picture of the new roof.[/quote]

Guess it doesn't matter...just imagine a rafter at 4/12 pitch with tongue in groove on the bottom (exposed to living area) and insulation in between.  On top, you are putting your metal roof.  So what goes between the top of the rafter and the metal roof?  OSB and tar paper?  OSB and 1/2" EPS?  Purlins and 1/2" EPS?

Hnmmmmmm...


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## colebrookman (Jan 21, 2009)

Mike from Athens said:
			
		

> [quote author="CZARCAR" date="1232585339]i dont get the picture of the new roof.



Guess it doesn't matter...just imagine a rafter at 4/12 pitch with tongue in groove on the bottom (exposed to living area) and insulation in between.  On top, you are putting your metal roof.  So what goes between the top of the rafter and the metal roof?  OSB and tar paper?  OSB and 1/2" EPS?  Purlins and 1/2" EPS?

Hnmmmmmm...[/quote]

That will be one of my projects this summer Mike.  You are correct, everyone has a different opinion.  I would go to your manufacturers web site for their recommendations so you don't kill your warranty.  You definitively need insulation over those rafters, try for R 40 or more if you can.
Ed


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## mikeathens (Jan 21, 2009)

Between rafters will be AT LEAST R-40.  It's what's _above_ the rafters that I am not certain about.


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## Ncountry (Jan 21, 2009)

I am not sure how much space is available above the insulation. ? I would make sure the space is well ventilated . A properly installed vapor barrier on the warm side of the insulation. Insulated well with no gaps for warm air to travel . Top of rafters... at least 1/2" plywood, 30# felt, and metal . Fail any of the 1st 3 steps and you have a good recipe for condensation . Oh yeah, do not forget to buy the screws designed for plywood ( shorter and larger diameter.)


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## 8nrider (Jan 22, 2009)

mike a vapor barrier on living side is a must. i would stay away from osb on any roof 1/2 cdx isnt that much more for a addition.proper vent inbetween insulation and plywood with both a soffit vent and some type of roof vent. if you have a roof paper (tar paper, or any other roofing uderlayment) inbetween metal and plywood. what will the condinsation hurt.


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## RAY_PA (Jan 22, 2009)

dont know if its right, but we built a 30x40 cabin with a metal roof and we did 'Purlins and 1/2” EPS? '


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## Hogwildz (Jan 25, 2009)

Check at your local roofing/building supply company. We used to do commercial buildings with metal roofs, and the decking we used was a plywood or osb with 3" polyisocyanurate insulation attached to the plywood/osb board.
Attach the decking onto rafters, then rosin paper, then screw the metal rood panels to the plywood or osb, whichever you get. If you use felt tar paper, there is a chance of the roof to stick to the paper and the paper to stick to the decking which can cause the metal panels to oil can when they heat up & expand.


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## woodsman23 (Jan 27, 2009)

It is so simple, nail down OSB cover with 30# felt paper (or better yet use ice shield (costly but work great)). Place metal roofing in place and use double sided tape at each seam (from place you get roofing) install foam baffels at each end to keep out bugs etc.. Screw down roofing with no less than 1.5" rubber gasket roofing screws ran down through the rises in the metal not the flat part. Screw humps but do not over thighten screws and use a punch to set a mark before screwing or the screws will walk all over the place. All done clean up, have a beer and look at what you have done in 1 day or less. We did a 63' x 22' metal roof (each side) in 1 day 4 of us over an asphalt roof using perlins 24 " on center.


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## mikeathens (Jan 27, 2009)

woodsman23 said:
			
		

> Screw down roofing with no less than 1.5" rubber gasket roofing screws ran *down through the rises in the metal not the flat part.*



HAHAHAHA...that is exactly what I have heard others say NOT to do..."if it's screwed through the ridges, you'll void your warran-tee".  When I did my 24X48 pole barn, no insulation so I laid it right on top of the purlins, and then screwed it through the FLAT part.

I think I'm stickin' with Hogs on this one...


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## woodsman23 (Jan 28, 2009)

Mike from Athens said:
			
		

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And that's funny why??? We did this 3 years ago and it has had no issues to date!. When you screw to the flat part leaking issues become a problem if a screw comes loose. laugh if you will i was just telling your ass what we did and we have had ZERO issues to date, moron...


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## billb3 (Jan 28, 2009)

Um, there's different kinds of metal roofing.
If you don't nail down which type you've got, you're gonna get all manner of conflicting experiences and recomendations.


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## ISeeDeadBTUs (Jan 28, 2009)

Use standing seam and avoid any attachment penetrations through the final roofing material


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## backpack09 (Jan 28, 2009)

Might I recommend a nice 25 year shingle?  ... Fewer opinions on how you should install those


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## Hogwildz (Jan 29, 2009)

Mike from Athens said:
			
		

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Mike, you have the correct way in mind. Of course do as the manufacturer instructs for your particular system.
As I always say, take some advice with a grain of salt.


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## kenny chaos (Jan 29, 2009)

The metal needs to go down on purlins for proper ventilation and doing otherwise (more surface contact, less air flow) collects too much moisture and causes early failure of the metal and the install will void any warranty.
We always nailed through the ridge which lets the metal expand and contract without loosening nails/screws or opening up the nail/screw holes.  It's kind of like installing vinyl siding; the siding is hung, not nailed tight.
Figure out your insulation requirements and what won't fit between the rafters can go either on top, on the bottom, or on both top and bottom of the rafters in the form of board insulation, then nail your purlins on top.  Do have continuous soffit and ridge vents!
As far as a vapor barrier, you're on your own with that one.  If each component needs to be inspected, the inspector will tell you what he wants.
Years ago, before the "I need a deck craze", was the "I want to finish my basement" craze.  The experts recommended a studded, insulated wall and the argument was always whether the vapor barrier went on the inside or outside of the insulation.  I saw it done both ways and years later there was rotted, molding drywall.  I don't know what is recommended today but I wouldn't use either.
I know that for exterior house walls, they finally caught on and exchanged a plastic vapor barrier for the breathable wind barrier.
Have you ever painted a wooden piece of outdoor furniture or a wooden barn wall?  Barn walls only get painted on the outside because moisture will penetrate the paint and will be happy sitting there rather than trying to get back out.  Not painting the inside allows the wood to breath.
I have a wooden picnic table that was painted completely.  In some spots the paint is peeling off and in others, the wood is getting soft.  It can't breath.
I know many smart people who "forget" certain code requirements in order to get a better job.
Be your own expert.  -Ken


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## mikeathens (Jan 30, 2009)

woodsman23 said:
			
		

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Lighten up, Francis.  I wasn't laughing at you.  I was laughing at the fact that it's so funny to get so many "right ways" and "wrong ways" to do the same job.  Go to the other hearth rip-off forum if you're going to be an ass.


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## Ncountry (Jan 30, 2009)

Most if not all manufacturers recommend screwing on the flats.I have been told by different factory reps that this was due to the chance of over tightening the crews and causing a kink that could cause the metal to fail or corrode prematurely. If every installer was diligent and never overtightened this would not be a problem. In that case if you are worried about a warranty You should stick to their rules. From personal experience and observation I have seen many roofs 50+ years old nailed on the ridges with 0 leaks . Installed in this manner an occasional loose nail or screw will rarely cause a leak. On the other hand something screwed or nailed through the flat that loosens up will usually leak. So are you happy with 20 years or so or do you want 50+. Then again will today's metal last as long as the metal of yesterday? I usually screw through the flats anyway.


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## woodsman23 (Jan 31, 2009)

Mike from Athens said:
			
		

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Who the hell is francis??? What is the "other rip-off forum??. I'm an ass mmm have agreat day dick.


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## kenny chaos (Jan 31, 2009)

Somebody has got to be the bigger man and stop this.


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## Ncountry (Jan 31, 2009)

Funny I just read a saying in one of my fishing mag...It says "the easiest way to look like a fool is to try arguing with one" ;-)


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## Hogwildz (Jan 31, 2009)

If you want a real nice roof that won't leak due to nails or screws, put a real standing seam roof on. Old school is alot of work, but lasts a long time if taken care of. Kickers, hand seamers etc, done it, loved it, makes a real true crafted roof. Or go with the new overlapping standing seam roofs, they come in alum. or galv. and one side is screwed down along the flange similar to a siding nailing flange, the next panel snap locks over that side and again screw the holed flange, etc etc etc. No exposed fasteners either old school or new. Seems, the cheaper barn roof metal roofing is slowly taking place of the good stuff. Either way, install as per manufacturer and then you have a warranty, if it is ever needed.
Don't feed the trolls.


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## Ncountry (Jan 31, 2009)

Hogwildz said:
			
		

> If you want a real nice roof that won't leak due to nails or screws, put a real standing seam roof on. Old school is alot of work, but lasts a long time if taken care of. Kickers, hand seamers etc, done it, loved it, makes a real true crafted roof. Or go with the new overlapping standing seam roofs, they come in alum. or galv. and one side is screwed down along the flange similar to a siding nailing flange, the next panel snap locks over that side and again screw the holed flange, etc etc etc. No exposed fasteners either old school or new. Seems, the cheaper barn roof metal roofing is slowly taking place of the good stuff. Either way, install as per manufacturer and then you have a warranty, if it is ever needed.
> Don't feed the trolls.



I would have to agree with 90% of the above. Read the fine print, often warranties are highly overrated IMO . I would take a roof screwed on the ridges properly over any warranty. That being said, Except for my own work I always followed manufacturer's recommendations . It is a lot quicker and you get a warranty.     Just sayin


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## mikeathens (Feb 2, 2009)

I got my roofing for my barn at carters.  It's been four years, but it went through the flats...I remember doing that because of the reason Hog stated.  The employees there said "go through the ribs, but if you overtighten, it will void your warranty".  I looked at the manufacturer's info, and they said go through the flats or you will void your warranty.  Guess it's whatever you're happy with.  I can see overtightening in the ridges cracking the paint and buckling the ridges, causing premature corrosion.  I think there was something about screws vs. nails, too.  My old house had the metal on the pole building nailed (with neoprene washers) through the ribs, and I spent some time up there repairing leaks.  I can't see screws loosening and failing like that.

Guess I'm most interested in what keeps the metal from sweating on the underside more than where to screw it down, anyhow.  I wish I had the $$ for standing seam.


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## johnn (Feb 5, 2009)

[quote author="ISeeDeadBTUs" date="1233189850"]Use standing seam and avoid any attachment penetrations through the final roofing material[/quote

  I installed standing seams years ago, and I must agree with those posts in favor! I`m haven`t been able to figure out how to install more than 1 quote you have two other fan`s, I make three. If you are familiar with and have ruled out this system I won`t elaborate,until you request. The bottom of these panel`s do screw down at the facia, to keep rain from blowing under, however these screws are very effecient.

  Also, I recently at a home improvement expo, saw a new system at least to me which I was interested in.

  The panels were made of metal had been put into a press and the result was a panel which looked like a cedar shake architechure.  the underside was coated with a foam type material (but better) making these panels around 1 inch thick. As a cedar roof would have about half inch step from one course to another,  these steps were an inch, but wouldn`t collaspe when walking on because of the foam.They were coated and looked just like any asphalt shingle you would nail down,same material.

The real selling point was the preenginered heat reflecting qualities,and were designed for re-roofing over existing shingles and claimed something like 40% reduction in attick heat, maybe more? I probably could find the pampletes if you would like,let me know.


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