Need some expert advice on a roofing question

[1akbig1bear]

I'm building my cabin completely off the grid on Kodiak Alaska where materials have to be delivered 8 hours away by a landing craft. Needless to say if the wrong materials are shipped then you have to work with what you have and that's what we did. Our material supplier shipped us 3/8" sheathing instead of the 1/2" that I had ordered, we didn't notice this until it was time to put the sheathing on our 10/12 pitch roof. Our goal was to put the roofing felt and then the metal roofing on but the rains came and we were only able to get the roofing felt put on and tacked down by scrap pieces of 2x4.
During my winter trip I noticed our roofing felt isn't holding up as best as we hoped. As I prepare for our summer trip up I have a professional question as to what to do? Could I simply add another layer of 3/8" sheathing and overlapping the previous 3/8" or should I go ahead and order 1/2" and put over top of the 3/8" then put ice and water shield on the entire roof this time, then the metal roofing? I don't ask if I should remove the 3/8" and simply replace because I would hate to waste all of what is up there and the $1400 I paid for it.
Please, need some good solid direction with this one.

Thanks

[akwoodchuck]

Too many water-entrapping layers= no bueno, especially in that climate....the 3/8" is all you need as far as bracing goes.....I would add another regimen of felt, then 2x4 strapping, laid horizontally, over that (preferably pressure-treated)....screw metal to 2x4s. I've had good results with this method......

[Ernest T. Bass]

Personally I think you'd be fine w/ 2 layers of ⅜ at that pitch, assuming the first layer is still in good shape. I'm not a pro though.. With all the roofing screws tying both layers together, I'm imagining it would be quite solid. Ice and water over the whole thing sounds expensive.. If you're going to get the roof on before winter this time, why not just another layer of felt?

As far as 2x4 strapping goes, there seems to be some conflicting schools of thought. I've heard that eliminating the air gap and putting the metal straight down on the felt leads to less condensation, and that's what I've done on my past couple builds.

I'm sure you'll get more qualified answers, that's just my $0.02

[1akbig1bear]

Akwoodchuck,

Thanks for replying but just want to make sure I understand correctly. 2x4 and not 1x4 and then there would be a gap between the metal roofing and the sheathing? Would I put the 2x4 or 1x4 horizontally or vertically? Assuming horizontally but just doesn't allow for anything to flow downhill if something were to get in.

Thanks so much again

[1akbig1bear]

Earnest T Bass,

Now you really have me thinking?

[akwoodchuck]

Akwoodchuck,

Thanks for replying but just want to make sure I understand correctly. 2x4 and not 1x4 and then there would be a gap between the metal roofing and the sheathing? Would I put the 2x4 or 1x4 horizontally or vertically? Assuming horizontally but just doesn't allow for anything to flow downhill if something were to get in.

Thanks so much again

Yes, horizontally...I prefer 2x4, less prone to splitting out, better bearing, price point basically the same....condensation/the occasional drip is actually less of an issue with this method, as airflow is vastly improved....

[Don_P]

I'm in the sealed deck camp but you've got another problem. Typically the metal manufacturers specify a 5/8" deck minimum for proper screw holding. I lean towards Akwoodchuck's method for where you are now.

[1akbig1bear]

Akwoodchuck,
How far apart would you put the 2x4's when placing horizontally? I'm assuming 16" but really have no idea.

[akwoodchuck]

24" max, 16" far better....I understand your transportation situation, but in for a penny, in for a pound 

[1akbig1bear]

Thanks you for the advice and getting it done correctly outweighs the extra money for materials.