# Whats the right way to do a metal roof?



## SouthernThunder (Jun 3, 2004)

I am wanting to put a new metal roof up starting from scratch (trusses will be here next week) and have got a different opinion on how to install it from everyone I ask. I understand there are two main issuses that need to be prevented. That is the fastners pulling out and sweating. 

This is what has been suggested the most. 3/4 plywood. tar paper. foil faced bubble wrap. furring strips. metal panel. 

There seems to be some disagreement about where the foil bubble wrap goes and also whether or not to use the furring strips. 

Does anyone have any usefull info here? Who has a roof that has been installed for a long time without issues and how was it done?


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## DavidUnderwood (Jul 5, 2007)

I do metal roofs for a living. Been to
workshops sponsored by the manufacturers.
Q and A sessions cover most topics at these.
On new work, in our climate(central NC) it
is common practise to put 2X4's on the trusses
to attache the metal. With free air circulation
all around, it will not sweat. If you use solid
plywood decking, use felt(tar paper) or red
rosin paper. No plastic, no where. Plastic will
cause sweat(condensation) dang near ANYWHERE
you use it. If painted metal is delivered to a job
site, especially in hot weather, try to keep it dry.
Water between sheets nested tight will cause
the paint to come off. Do NOT cover it with plastic.
That will cause sweating, and will also make the
paint peel. If you use solid plywood and felt, there
is no reason for furring strips. Elevating the metal
on strips will leave an air space, thereby allowing
the metal to sweat. And never apply metal to treated
wood. It is extremely corrosive. In 25 years Ive learned
from my mistakes. Yet and still, someone now and
then wants me to do something that I know is wrong,
insisting that a friend told him how it should be done.
I reccomend he hires this "friend" to roof his house.


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## SouthernThunder (Jun 3, 2004)

Hey David, thanks for the reply and good information. What spacing would you suggest for the 2x4s on the trusses (which are 16oc)? Is there anything that can be done for rain noise reduction if it is just the metal roof on 2x4s? 

Which method would you say is the longest lasting and toughest, plywood/tarpaper or the 2x4?


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## rambler (Jan 20, 2004)

Is this a storage building (heated or not), a livestock building, or a dwelling for humans? Not sure what you are building, makes a huge difference on the amount of moisture & how to construct it.....

--->Paul


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## SouthernThunder (Jun 3, 2004)

sorry, forgot to mention, this is a 2 story house in oklahoma.


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## Beeman (Dec 29, 2002)

SouthernThunder said:


> I am wanting to put a new metal roof up starting from scratch (trusses will be here next week) and have got a different opinion on how to install it from everyone I ask. I understand there are two main issuses that need to be prevented. That is the fastners pulling out and sweating.
> 
> This is what has been suggested the most. 3/4 plywood. tar paper. foil faced bubble wrap. furring strips. metal panel.
> 
> ...



www.metalroofing.com has a forum and a list of manufacturers that will answer your questions.

I don't know it I'd use the furring strips, just deck it, seal it and then put the metal. I used foil/foam/foil insulation instead of bubble. it's made by environmentally safe products called low-E insulation.


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## Up North (Nov 29, 2005)

We have a dairy barn with Asphalt shingles. I would like to cover it with white 
roofing steel. Furring strips or no?


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## Ramblin Wreck (Jun 10, 2005)

DavidUnderwood said:


> On new work, in our climate(central NC) it is common practise to put 2X4's on the trusses to attache the metal. With free air circulation all around, it will not sweat.


That's how we did it on my house and garage (and several other family member projects too), and I've (we've) had no problems with sweating. We're in the South, so it might be a different issue in other climates with snow loads.

One other comment/suggestion: Regardless of what underlayment/structure you go with, make it as square as you can. It makes for a much quicker, easier install.

Good luck.


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## fantasymaker (Aug 28, 2005)

The metal is going to sweat.
The 2 X4s under it will give space for air circulation to help dry the sweating.
if you must insulate near the metal use Spray foam insulation sprayed directly on the metal.
That will put the condensation point inside the foam where the air cant get to and thus no condensation,
If your not doing that reread DavidUnderwood's post.


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## TedH71 (Jan 19, 2003)

When I helped build houses for Americorps..we installed metal roofs. Was told to put 2 by 4s then put vapor barrier (forgot what type) over it then the roof over that and it was all screwed in. No furring strips, etc. Main reason for metal roofs is that it will reflect heat off the house and not need replacing in for 50 years compared to 20 years on your standard shingle roof.


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## Farmerwilly2 (Oct 14, 2006)

All of the buildings I've put up to date on the place are uninsulated. I use 2x4 nailed to the rafters and then the steel. I've not had any condensation to date. The shed has a gravel floor, damp when it rains. The poultry house has a wooden floor, but birds that poop and breathe. No condensation at all. Hoping David writes back, I will be replacing the roof on the house when the time comes with metal roofing. I'd like to know what the manufacturers regarding fiberglass batts and a vapor barrier beneath the rafters.


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## sugarbush (Jul 15, 2007)

And I always thought that the biggest debate in metal roofing was whether to screw it on the ridges or plains!


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## Farmerwilly2 (Oct 14, 2006)

sugarbush said:


> And I always thought that the biggest debate in metal roofing was whether to screw it on the ridges or plains!


I'm a 'nail it through the ridge' kind of guy. I've had to tear off screwed down roofing. I'd rather rub down a bobcat with a handful of broken glass.


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## SouthernThunder (Jun 3, 2004)

When people say a metal roof is good for 50 years what exactly goes bad after 50 years? Does it start to rust out or need to be re-fastened or just repainted? My problem is there is chance I might still be alive in 50 years but probably will not be able to re-roof this joint.


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## sugarbush (Jul 15, 2007)

Well providing that it comes painted and you don't get scratches in the paint while putting it down or hail/wind damage it should last forever......it will need to be maintained just like anything else.


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## ET1 SS (Oct 22, 2005)

I sprayed foam onto the underside of our roof, we are very happy with it.


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## Farmerwilly2 (Oct 14, 2006)

ET1 SS said:


> I sprayed foam onto the underside of our roof, we are very happy with it.


Could you give a little more detail. As I recall you set up a metal building to live in. Is this sprayed foam the only roof insulation? Did you rent or buy a sprayer? How do you handle moisture levels in your home?


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## ET1 SS (Oct 22, 2005)

Yes I built a steel building. 60foot by 40foot and 12foot eaves.

I sprayed foam onto the interior roof and walls, about 1.5 inch thick. It solidified the sheet metal. It sound deadened it. I then hung R-30 fiberglass batting against that foam, and held it in place with wood paneling.

The foam that I used comes in a pack of two pressurized bottles. The two components mix in the nozzle as it is sprayed out. The foam is an epoxy that sticks to everything it touches. It heats itself to 200 degrees as it expands and hardens. It is hard within about 30 seconds. It is pressurized with nitrogen, as it expands it out-gasses mostly nitrogen. You can spray it with only a paper mask over your face.

We have a propane water heater that sucks make-up air from the house and vents it outside, this lowers the inside humidity some.

And we have a stove that burns wood / peat / coal. The stove also removes humidity from the house.


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## Farmerwilly2 (Oct 14, 2006)

I think that's the foam I saw from Northern Tool? Any problem keeping the spray at a consistent thickness? I wonder if it's like the 'instapak' foam I used in a shiping dept. years ago. Thanks for the answers.


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## artificer (Feb 26, 2007)

Up North said:


> We have a dairy barn with Asphalt shingles. I would like to cover it with white
> roofing steel. Furring strips or no?


For the best quality job, which lasts the longest, use furring strips. If you don't, the paint/coating on the bottom can be abraded by the the stones in the shingles. If you get any moisture in there, then it will rot out from the bottom. Granted... it'll take years/decades to do so, but for the small cost and additional time, it makes sense. Its also easier to screw/nail the sheets down, since you now have a know good fastening surface. 

Michael


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## ET1 SS (Oct 22, 2005)

A single 600 square foot of foam kit consists of two 20 pound bottles, 30 foot of hoses and a spray nozzle.

DOW chem markets it under the name "Froth-pak"

I bought a generic that is otherwise identical that is marketed under the name "Touch-N-Seal". The generic sells for about half the price as Dow's product sells for.

This foam once it is cured is hard like an ice-chest foam. It is not spongy and it is not open-celled.

I do not know what kind of foam Northern Tool markets.


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## Up North (Nov 29, 2005)

artificer said:


> For the best quality job, which lasts the longest, use furring strips. If you don't, the paint/coating on the bottom can be abraded by the the stones in the shingles. If you get any moisture in there, then it will rot out from the bottom. Granted... it'll take years/decades to do so, but for the small cost and additional time, it makes sense. Its also easier to screw/nail the sheets down, since you now have a know good fastening surface.
> 
> Michael


Thank You Michael.


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## DavidUnderwood (Jul 5, 2007)

When you use Kraft-Faced(vapor barrier) fiberglass
insulation, the paper always goes towards the living
quarters. Building code everywhere I've ever worked
calls for an air space between insulation and roof,
and some means of ventilating that air space.
I prefer screws in the flats over nails on the humps.
I've seen both leak, and/or fail. Nothing is perfect.
They do make the lil rubber washers better than 
they used to.
On the question of furring strips. Pros and cons
all over the place. The air space created encourages 
condensation. Not nessecarily enough to be a problem.
If there were enough moisture ( local climate), the water
would run down the metal, dampening the strips and
eventually softening the wood so the screws (or nail) 
can pull out. I don't have a problem with screwing the
metal to the old shingles. Never heard a manufacturer
caution against it. If it worries you though, put down a 
layer of felt or rosin paper between them. Most important 
is put your fasteners in solid wood, and use enough of them.


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## farmergirl (Aug 2, 2005)

Good thread! I'd like to install a metal roof on our 1500 sq ft doublewide mobile home. The existing roof is probably the original material from back in 1985 when the home was built. Would I need to rip the concrete shingles off before attaching the metal roof?


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## Beeman (Dec 29, 2002)

farmergirl said:


> Good thread! I'd like to install a metal roof on our 1500 sq ft doublewide mobile home. The existing roof is probably the original material from back in 1985 when the home was built. Would I need to rip the concrete shingles off before attaching the metal roof?



Concrete shingles??? I'm guessing they are fiberglass shingles. No you don't need to remove them. Place 30lb felt(tar paper) over them and roof over that. You could also use insulation as previously mentioned.


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## mellba (Oct 15, 2004)

We've got an old cabin that has a metal roof that is probably 50 years old and we'd like to replace it. Is there any way to put a metal roof over the old one or do we have to tear off the old metal?


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## Beeman (Dec 29, 2002)

The condensation problem with metal is just a science thing. If you can eliminate the difference in temp on the both sides of the metal or have little or no moisture you won't get condensation. 
The spray on insulation does the job but... If there is the slightest breach (hole) in the insulation that allows moisture to contact the metal when it is different temps on either side you will have condensation. I wonder if that small spot of condensation will get between the metal and insulation and cause problems over a long period of time?


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## ET1 SS (Oct 22, 2005)

Beeman said:


> The condensation problem with metal is just a science thing. If you can eliminate the difference in temp on the both sides of the metal or have little or no moisture you won't get condensation.
> The spray on insulation does the job but... If there is the slightest breach (hole) in the insulation that allows moisture to contact the metal when it is different temps on either side you will have condensation. I wonder if that small spot of condensation will get between the metal and insulation and cause problems over a long period of time?


Our spray-on-foam is an epoxy.

Part A mixes with part B, this epoxy sticks very hard to everything it touches.

I sprayed it directly 'up' onto roofing that was over my head, and it stuck right there. I did get a small bit of 'over-spray' but I think that such is normal considering the process.

I do agree that anywhere you have metal that is exposed to air flow, then you have the possibility of condensation.

When it is -10 outside and a layer of ice covers the roof, then you know that the roofing must be cold. Any warm humid air inside that touches the roofing should condensate water.


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## Beeman (Dec 29, 2002)

mellba said:


> We've got an old cabin that has a metal roof that is probably 50 years old and we'd like to replace it. Is there any way to put a metal roof over the old one or do we have to tear off the old metal?


 I would say the best way would be to remove the old metal. I'm sure you could somehow place wood strips over the existing metal and cover it but is it worth it and how much additional weight is being added to an old structure?


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## farmergirl (Aug 2, 2005)

Beeman said:


> Concrete shingles??? I'm guessing they are fiberglass shingles. No you don't need to remove them. Place 30lb felt(tar paper) over them and roof over that. You could also use insulation as previously mentioned.


Sorry. I meant asphalt shingles, but truly I don't know the exact composition :baby04:


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