Questions about metal roof

[jbarker855]

Hi fellas-
I'm planning on building a small (12 x 22) shed to house some snowmobiles for a few years until I get enough time and money to guild a bigger garage. I would like to use metal roof panels for the roof. I am curious if they can be fastened directly to roof rafters which will be spaced 16" on center. From what I have read, it looks like most people lay down a few 2 x4's perpendicular to the roof rafters and then fasten the metal roofing to those. Any advice is appreciated.
This thing will be relegated to a firewood shed after a few years, so I'm not looking to build this thing to the max durability, although of course I want it to be safe. Thanks in advance for any tips!
-Jay

 

[Duffster]

Short answer.....No.

 

[jimmyj]

You need to put something up on the rafters or the sheeting will sag in between. I have built several sheds like this and either strap it horizontally with 1x4 lumber or even better, clad the roof with OSB or plywood (1/2") and then put the metal on. You won't regret the small extra cost and work. The wood controls noise and condensation and makes it much easier to install the steel. Also, if you have to walk on the roof (to clear snow or whatever) it won't bend underfoot.

 

[FredH]

As above , Advise No . Metal roofing's strength is through the length not side to side . 2 x 4 is kind of overkill . I have always used 1 x 3 or 1 x 4 stock and fastened to that . Depending on the pitch of roof , a 8' metal panel could have 3 fastening points or more . The steeper the pitch would equal less possible snow load on roof thus one could use cross pieces at top , center and bottom for fastening 8' metal panels .

Fred H.

 

[crusty 1]

Jay, I,d use sheeting followed by 1by4 then attach metal to the 1by,s. The roar in a heavy rain could drive you crazy without the sheeting and won,t add that much to the costDave

 

[Redneck in training]

I live in a house with metal roof. There isn't sheathing under the panels. The panels are nailed to horizontal 2X4. The nails have rubber gasket to seal and are nailed to the rib somewhat off center and in 60 - 70 degree angle. The nail makes a "dimple" in the rib and because the dimple is on side of the rib it can't hold water. The builder used nails instead screws because of self healing sheet metal. The nails pull the galvanizing alloy in the hole and seal the edge while screws wouldn't do it.
Actually sheathing under the panels will cause condensation on the bottom of the metal and also holds heat at night. Without the sheathing the attic cools pretty quickly after sunset.
Before we installed attic insulation the noise was very loud during rain but with insulation it is hardly noticeable.

 

[jbarker855]

Thanks for all the responses. Seems like a no-brainer now. I will affix horizontal strips or sheathing or both.

 

[flusher]

Hi fellas-
I'm planning on building a small (12 x 22) shed to house some snowmobiles for a few years until I get enough time and money to guild a bigger garage. I would like to use metal roof panels for the roof. I am curious if they can be fastened directly to roof rafters which will be spaced 16" on center. From what I have read, it looks like most people lay down a few 2 x4's perpendicular to the roof rafters and then fasten the metal roofing to those. Any advice is appreciated.
This thing will be relegated to a firewood shed after a few years, so I'm not looking to build this thing to the max durability, although of course I want it to be safe. Thanks in advance for any tips!
-Jay

I used 2x4 purlins across the rafters on my 20x28 shed. It's the correct way to install a metal roof.

 

[PILOON]

I have observed that laying metal directly over sheathing results in very rapid corrosion of the underside of the metal due to the condensation being trapped between metal and wood.
So much so that in less than 10 years a galvanized roof was total scrap.
You need to let air circulate under the metal!
That condensation can get so bad (depending on climates) that on some cases the dripping actually wetted attic insulation to the point that the gyprock ceiling in a home was costantly water damaged.

My wood shed is tin roof, and in spring with cold snow on top combined with warm spring air inside the shed, the condensation is so severe that it literally rains inside!

 

[Arky217]

I plan to put a metal roof on the retirement home that I'm building. The roof will be trusses with 2 foot spacing. Over the trusses will be Avantech Zip roofing panels. The Zip panels will have the seams taped over with Avantech's Zip panel tape. (They claim this will make the roof rain tight up to 120 days). The insulation will be cellulose in the ceiling.

I have heard just about every way there is to install metal roofing panels to prevent condensation:

Some say to put down a 15# or 30# layer of felt over the sheathing, then the metal panels; in other words, not to use purlins or the metal will condensate like crazy; enough so that the water will find it's way through the layer of felt.

Others say just the opposite, that putting metal panels over sheathing (or sheathing with felt) will enhance and trap condensation and accelerate corrosion of the under side of the metal; and that you should put down 1x4 purlins (with drain holes cut into the bottom of the purlins to allow trapped water to run down the roof), then the metal over the purlins.

Avantech says that with their Zip panels, just put the metal directly over their sheathing. That the superior resin in their Zip panels makes even a layer of felt not necessary.

So far, I am leaning toward Avantech's recommendations, (but I still wonder how any trapped condensation will escape from between the sheathing and the metal, what with the metal tightly against the panels).

What say you metal roofing experts ?

My only experience with metal roofing panels is:

I build a 12x12 storage shed. I used boards for the roof. Put felt over the boards, then the metal. That was 3 years ago; I haven't noticed any problems yet.

About the same time, I built a 20x24 carport. Just like the commercial ones, I put the panels horizonally directly over the metal 'trusses'. There are times when the condensation is so severe that it appears like it's raining under the carport.

Thanks,
Arky

 

[bstrom]

I have observed that laying metal directly over sheathing results in very rapid corrosion of the underside of the metal due to the condensation being trapped between metal and wood.
So much so that in less than 10 years a galvanized roof was total scrap.
You need to let air circulate under the metal!
That condensation can get so bad (depending on climates) that on some cases the dripping actually wetted attic insulation to the point that the gyprock ceiling in a home was costantly water damaged.

My wood shed is tin roof, and in spring with cold snow on top combined with warm spring air inside the shed, the condensation is so severe that it literally rains inside!

No disrespect but I have two sheds with metal roofing on spaced 1x4's and a house with a metal roofing on sheathing with tar paper between the roofing and sheathing and a vented attic and haven't experienced any condensation problems with either method. Maybe it is more a problem in your climate? I'm in Maine and we get plenty of snow but it seems to slide pretty fast. The pitch is only 6/12 too. It comes down all at once with a crash sometimes!

 

[Brad_Blazer]

I made heavy trusses and ran purlins between them about 36" on center. No rafters.

 

[tallyho8]

The correct answer is YES!

OP said he wants to build a very inexpensive shed that will just be used for firewood once he builds his new garage. He has been given instructions on how to build an expensive roof for a home which is not what he desires.

With a roof only 12' wide it is perfectly permissible to screw the panels directly to your rafters as long as your rafters are secure and do not need any extra 2x4 bracing which would probably not be needed on a roof that small since your rafters will only be 6' long unless it is a single sloped roof and then they are only 12' long.

The trick to it is to run the metal panels horizontal on the rafters instead of vertical. As long as you have enough slope on the roof it will be sturdy and not leak. It is best when running panels horizontal to use low rise panels and not R-panels.

Most of the small carports and sheds sold in our area have the metal running horizontal as in the image.

If you use metal siding it may be run horizontal also as long as the walls are braced properly.

Your firewood will remain dry and safe with much less expense.

 

[MikeD74T]

Don't underestimate the snow in your area. It doesn't cost a lot the build a good shed. Build your own trusses with 2x4s -24" OC, 6" or 8" pitch. Whether a cheap building falls on snowmobiles or woodpile it will be a total loss. The size of the purlins depends on span & spacing. Excess span a/o excess spacing will result in sagging/buckling ultimately reducing longevity. Money saved by spreading the purlins can be wasted if you have to walk on the roof & it gets damaged. Especialy important when ice/snow falls from one roof to another, ie from a main roof onto a leanto. My barn has 50' trusses spaced at 40" with 2x4 purlins spaced 24", 5/12 pitch. It will & does hold 2' of dry snow. My bridge has 2x4 rafters 24" oc 12/12 pitch &1x5 purlins 24"oc & no snow accumulates on it. In all cases the metal roofing is attached with gasketed screws.
Tallyho, With all due respect - your carport wouldn't last past the first lake effect snowstorm in the OP's area. Take a look at their snowfall numbers & compare to LA. NWS Buffalo Climate Information - Buffalo Monthly Snowfall (2000s) MikeD74T

 

[tallyho8]

The image I posted was just to show how horizontal roofing is run. His building must have much more pitch in a heavy snow area and also he is making it out of wood with rafters on 16" centers. 26 gauge metal on 16" centers with a good pitch should be sturdy enough.

 

[Redneck in training]

The image I posted was just to show how horizontal roofing is run. His building must have much more pitch in a heavy snow area and also he is making it out of wood with rafters on 16" centers. 26 gauge metal on 16" centers with a good pitch should be sturdy enough.

OP is in NY where they get lot of snow. Horizontal ridges would prevent the snow sliding down and possibly accumulate enough to cause damage to the roof or the shed. Since the building is small nailing 2X4 on the trusses is way to go. It will add very little expense IMHO. In fact OP could place the trusses farther apart to save on cost and then nail the 2X4 on the edge to increase load-bearing capacity.

 

[QRTRHRS]

I swear by 1/4" bubble wrap with foil on both sides. Comes in six foot widths. Is relatively inexpensive. I have not heard that it will lead to premature metal rusting. Cuts the sound from a heavy rain way down. Eliminates dripping totally. Lay it over the purlins starting at the bottom with a little overlap same as tarpaper. Secure the roof tin directly over it.