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bluewillo
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# Posted: 12 Aug 2013 17:59
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HI ya'll. I thought, instead of hijacking someone else's thread, I'd ask my questions here.
Today I learned how to figure the pitch of my roof (google is indeed my friend!)
Here's my info: 16 x 20 cabin. The pitch on the (beautiful, may I say) green metal roof is indeed 12/12. There are no trusses, the "ceiling" is just the metal roof and the 2x6 or maybe 2x8's. No cross beams. It does get rather windy out there, so I am thinking about adding, about 4 feet down from the ridgline, 2x6 crossbeams to sturdy it up (and I'm digging a root cellar, just to be safe.)
The cabin construction is just the outside OSB and the inside framing lumber (I bought it like that, hubby had a *^$%^#^%$&^(* fit and is not a part of this project).
My question is: which is the best and cheapest (yes, I know those two words seldom show up together in the answer!) way to make the roof watertight? I'm allergic to mold and mildew, so that is a big concern
Thanks in advance for your answers, and remember, when I bought this place, I saw the DREAM (can I get an amen, sisters?) not the WORK!
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bluewillo
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# Posted: 12 Aug 2013 18:20
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Oh, and I'm in Northern Michigan, lots of snow!
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PatrickH
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# Posted: 12 Aug 2013 19:01
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personally if it was a home I was going to live the rest of my life in first I would remove the steel and add 5/8 plywood I would not use osb on a steel roof, then tar paper and reinstall roofing with new screws that would be a minimum for me I would also want to know the size and spacing of the rafters I may modify those as well,just what I would do if it was mine but me and hard work go together really well.
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Martian
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# Posted: 12 Aug 2013 19:22
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+1 on what Patrick said.
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MtnDon
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# Posted: 12 Aug 2013 20:01
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Quoting: bluewillo No cross beams. It does get rather windy out there, so I am thinking about adding, about 4 feet down from the ridgline, 2x6 crossbeams to sturdy it up
There are two kinds of 'cross beams' as you call them. One is a 'collar tie'; the other is a 'rafter tie'. They both have a specific task and are not interchangeable. Note; you may well gets lots of differing opinions on this matter; there are many bldgs that do not have either thant are still standing after years. That is not a guarantee that everyone will have the same results.
With a steep 12/12 pitch you may not have to worry over snow loads, but those high winds can also exert large loads that can try tp spread the wall tops.
See image below for details
What is the purpose of each?
Collar Tie; keeps the roof from peeling open at the ridge under certain high wind conditions. They work best near the peak but can be anywhere in the top third as illustrated.
Rafter Ties; keep the wall tops from spreading apart. Ideally on the wall tops and nailed to the rafters. They can be higher in the roof triangle as illustrated. As they are placed higher in the triangle they exert forces on the rafters that may overload standard sized rafters. Rafters often need to be sized upward like a 2x8 instead of a 2x6. There are tables and notes in the IRC.
The size of the rafter ties can vary; id only doing the job of a tie, 2x4's are okay for this size bldg. If used to secure a ceiling they need to be bigger and if used as a floor for the attic even bigger again. There are tables and online sizing tools. Some are referenced in the forum reference section.
Quoting: bluewillo My question is: which is the best and cheapest (yes, I know those two words seldom show up together in the answer!) way to make the roof watertight? I'm allergic to mold and mildew, so that is a big concern
Best and cheap are opposites. Sorry, but you knew that already 
The way it sits it is probably watertight as in not letting the rain in. There is the possibility of underside condensation, which as noted elsewhere can play havoc with any insulation up there.
At this point, in the long run Patrick has a superb idea. Remove the metal roofing. Sheath the roof; if cost is a factor 7/16 OSB can do the job if the rafters are no more than 24" OC.
(( You will get arguments on this as well;; 5/8 material is better than 7/16. Better but not absolutely necessary. Ditto on the plywood vs OSB argument. Thing is when there is a budget crunch the OSB gets the job done and meets residential code. ))
Not only will the sheathing remove the condensation problem but it will strengthen the roof immeasurably. Then #30 felt (tar paper) or synth membrane. Then put the metal back on. Best to use new screws; easier and quicker and better.
Rafter & Collar Ties illustrated.
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bluewillo
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# Posted: 12 Aug 2013 20:15
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Thanks, all, especially Patrick. I will break the news to my "crew" (I've 2 grown strong sons who are totally onboard with this project). One used to do roofing for a living...he's gonna look at me and go "Oh, &%*&* Ma, I KNEW we were gonna have to do that!".
Forgot to mention, there is a loft (I've no idea how tall this house is, I'm short, so to me, it's really really big as in I'm gonna finally have at least a 20' Christmas tree (with the back all pruned off  this year!} that covers about 1/3 of the "downstairs".
I've been reading here for months, I knew I could get the answers I needed without involving the dreaded building inspector involved. Since the building was up when I bought it, the state has no interest in building permits...until I do anything on the outside, like adding the covered porch which will make it comply with our townships one of 2 building requirements.
Thanks again, and I'll be asking again!
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