Author Topic: metal roofing  (Read 4864 times)

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Offline lee5267

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metal roofing
« on: January 21, 2008, 01:17:56 PM »
I have read and seen some people who have simply run 1x4's over their rafters at 20" OC and installed their metal roof directly over the top with no sheathing.  In a rather moderate humidity climate will condensation be a problem with this if you have a continuous roof vent and soffit inlet vents?  I was going to put roof insulation in and t&g pine as the finish underneath the roofing.  This is what I am wanting to do on the 14x24 little house so as not to mess with sheathing if possible. Any thoughts?

Lee
« Last Edit: January 21, 2008, 01:33:09 PM by lee5267 »

Offline John Raabe

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Re: metal roofing
« Reply #1 on: January 21, 2008, 04:04:54 PM »
Roof sheathing does more than just provide a deck to nail the roofing to. It serves as a diaphragm and locks the rafters and roofing together into a structurally integral unit helping to resist wind and earthquake forces. It helps stabilize the whole building.

That said, there may be areas of the country where this can be done away with and the house may never need this level of structural support.

I am not a roofer but at a minimum I would think there should be a self draining waterproof barrier under the roofing. Just as you have tarpaper or another type of secondary roof under a shingle roof.

Here is a video on batten installation for metal roofing: http://www.expertvillage.com/videos/installing-steel-roofing-framing-batten.htm
Here is another How to on metal roofs: http://www.extremehowto.com/xh/article.asp?article_id=60253
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Offline MountainDon

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Re: metal roofing
« Reply #2 on: January 21, 2008, 04:45:08 PM »
I believe metal makes a great roof. Metal is also probably the worst when it comes to the chances of condensation forming on the underside because it's temperature will change much more rapidly than most other building materials, with the exception of glass maybe.

I'm planning on a metal roof on our 14 x 26 little house. I plan on OSB, then #30 felt, then the metal.  I'm doing OSB over the rafters because it does get quite windy at times. As well the OSB dampens the sound of the rain on the metal somewhat. And I feel more comfortable doing the metal over felt that's over OSB, rather than doing metal over felt that's just supported here and there by purlins. I'd mis-step and fall through sure as heck. Furthermore that will allow me to dry in the roof and then order the metal to the measurements I take off the OSB covered roof, rather than do it off my drawings, which I do feel are good, but....

The best method may be sprayed on foam like Icynene. But it's too expensive if I could even find an installer who wanted to wind his way up over the bad roads through the mountains.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline Redoverfarm

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Re: metal roofing
« Reply #3 on: January 21, 2008, 05:57:21 PM »
Another down side to perlins vs. sheeting is with perlins you are more likely to get bug,bees and insect infestation into your insulation not to mention bats if you live near a wooded area.  With sheeting you can put screened vents as the convientional overhang ventilation and not allow for the insects access to the insulation area. 

Offline lee5267

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Re: metal roofing
« Reply #4 on: January 21, 2008, 07:15:38 PM »
Thanks for all the replies,

One of my main concerns is applying the sheathing on such a steep pitch of 12 in 12.  Will an 8in12 be a little more manageable for a someone not accustom to roofing?  I felt that I could apply the metal roofing with the help of another person with the use of a ladder through the rafters with no sheathing easier than crawling around on top of the steep pitch sheathing.  Since the idea of no sheathing is not optimum although possible, will the 8in12 roof be much easier to manage with the sheathing?  Trying to figure out all the options and best options for me as well.  This will only be a cabin I spend a few weeks at per year. 

Thanks again,

Lee


Offline MountainDon

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Re: metal roofing
« Reply #5 on: January 21, 2008, 07:43:34 PM »
Anything over 4:12 requires the use of safety restraints, IMO.

Personally I would not want to do anything over 8:12 myself, anymore. But maybe that's just me.  ::)

And even a 4:12 metal roof requires more caution than asphalt shingles if you're on top of it. I have one particular pair od especially "sticky" gum soled shoes just for going up on my metal roof.

Even if you install the metal panels as you describe, you have to install the ridge cap/vent to finish off the roof and that has to be done from on top.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline glenn kangiser

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Re: metal roofing
« Reply #6 on: January 21, 2008, 08:08:43 PM »
If you will want to stand up in the attic of the 14x24, I would suggest getting help to do the 12/12 pitch as it gives just enough room to stand up in the center.  8/12 will not.
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Offline Redoverfarm

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Re: metal roofing
« Reply #7 on: January 22, 2008, 06:34:46 AM »
Lee  I have a 16X40 cabin which will incompass a loft as well.  I was amazed by the difference in the headroom of a 8/12 when compared to a 10/12 roof.  I guess you could say that mine is sort of ballon framing(with logs) but the 10/12 gives alot more headroom along the side(knee walls). The ridge heigth will stay the same in eaither case.  Have you tried to lay it out and see what you would end up with?

As far as the installation You should probably grab a couple extra people to assist. 4 is ideal as two on the ground to cut and hand up the sheets while two on the roof to install.  I used sheeting and when it came time to install I was blessed by my tractor bucket.  I just used a 16' wooden ladder which I rested in the bucket and laid the ladder on the roof. The sheets are generally 3' wide and you could easily work off the ladder to attach it to the sheeting. When it came time to move over the two on the ladder just moved to the ridge cap and I relocated the ladder down the line.  You could also tack 2X4 to  work off of but there is a lot of moving them down the line.  A friend of mine installed his with the use of his truck bed by resting the ladder against the cab wall and allowing it to lay flat on the roof. Usually requires a 16-20' extension in the truck. Of course this wouldn't work on a two story but 1-1/2 it would if the ground wouldn't prohibit it. c*

 

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