Cabin addition

Greetings, first time poster here.

I am planning two additions to my remote cabin. The cabin is currently a 20' deep by 28' wide garage package with a 4/12 pitch roof that used 5/8" OSB for roofing with H-clips and ashphalt shingles. I want the end result to be a 30' deep by 40' wide outside shell with the rear roof to maintain the 4/12 pitch but the forward roofline to become a 2/12 pitch. The side addition will be added interior heated living space while the front addition will be a screened in porch/storage area. The current outside wall will remain in place to support roof load and maintain a thermal barrier for exterior elements.

My plan is this....In the area of the side addition I will install new trusses that are engineered and built for the two different slopes but for the rest of the original 28' front I would like to run new 2"x8" from the new screened exterior wall up to the original ridgeline. I will cut the appropriate angle into the new 2"x8"s so that it forms the correct 2/12 pitch and fasten them to the original trusses (through the 5/8" OSB) after having removed the original ashphalt shingles. I will also support the new 2"x8"s above the existing wall with a 2"x8" standing vertically. I will also attach 2"x4"s as a rafter that will run from the new exterior wall to/and tie to the original roof trusses. The new exterior wall will be constructed of 2"x6"s with a 5 1/2" wide (3-2"x6"s and 2 thicknesses of 1/2" plywood laminated together) beam on top to support the new 2"x8" homemade roof trusses. I believe that the current truss system is 24" on center but could be 16".

I plan on using a metal ribbed roofing material to help dispatch the snow that likes to build up on the roofs up here in the north.

Does all of this sound reasonable or will I end up with a sagging roof line?

Thanks in advance for any advice given.

By the way all supplies are to taken in in winter by snowmobile, anyone want to come help and get in some of the best ice fishing in the world?
Tony

 

I'm not a carpenter but a roofer and my advice is to ice and water shield the entire roof before installing the metal due to the very low slopes.
Sounds like a lot of fun though.