Your big mistake was allowing the butt ends of the clapboard to make contact with the roofing whether it was painted 1st or not. You should have laid a wooden strip on the roof and against the cheek prior to clap installation. The strip should have been at least 1/4" to 3/8" thick to hold the clap above the roof.
If you paid attention when you were removing the original mat you'd have noticed it was the butt ends in contact with the roof most severely damaged. It's the same regardless of red or white, clap or shingles. The only products not overtly affected by water and debris are vinyl, Fiberglas, slate and the old banned asbestos fiber shingles.
Wood in contact with the roof, (painted or not) will prematurely age and erode. Debris builds up between siding and roofing, (dust, leaves, pine needles, animal fur, sand, bird down, bug carcasses, dead snakes, you name it I've found it. It all traps water so much longer than if it were open to wind and air movement it ain't funny. Mold/mildew begins, builds and infiltrates the mat, causing it to hollow and swell making room for water/ice sublimation into the wood fibers. Consider yourself lucky to get 2/3ds the life expectancy of the material, the higher the moisture levels,(rain, snow humidity) in your area the shorter the life span.
P.S. if no one mentioned it, SST ring nails to fasten the clap to the house and nailed into the wall studs not the voids between. Lastly any place you joined 2 sections of clap together you should place a felt spline behind for extra weather protection for when the joint dries up and opens. The joint will swell back up shortly after the rain begins but not always before some water makes it between and runs down the wall.
Work smart not hard!
Never bite the hand that looks dirty
Last edited by Ghidrah; 07-18-2015 at 11:48 AM.