Hello,
First time post here. I need to repair my detached garage roof, as the asphalt shingles are crumbling. underneath the one layer of shingle is a layer of underlayment(like a tar paper), and underneath that are wood shingles. I checked inside the garage, up in the rafters, and all wood hingles look in great condition, and there is no sigs of leakage. My question is, can i just take off the layer of asphalt shingle, and underlayment, and put on a new layer of heavy weight underlayment and a new course of asphalt shingles? The other option is to completely strip the roof of both asphalt and wood shingles, and purchase and apply 1/2 inch plywood decking to the roof rafters, and then tar paper and shingle over that. These are 2 very different options, with different costs, and time associated. I am doing this myself, with the help of my dad, brother, and buddy, all of us who have at best intermediate skills. Thanks for your insight.

 

I'd recommend removing the wood shingles, so that you have a perfectly flat surface for your new shingles. They will last longer and lay flatter that way. You'll also want to apply new drip edge around the perimeter once you have that new sheathing on.

 

There is no question at all here. Strip off all shingles. New sheeting on the roof, and new shingles. Do it right. Good Luck

 

Rip it all off, inspect everything and redeck it.

 

Could you give a link to steps how to replace wood shingles and
most important what's the tricks and not-to-dos.

 

I fould some links that describe how to replace wood SIDING shingles:

http://www.ehow.com/how_17557_replace-shake-shingle.html

http://www.naima.org/pages/resources/library/html/BI403.HTML

but I could not find if shingles should be painted (or covered with protective stuff) on back side before installation.

 

If you have wood shingles on there now, you most likely don't have any built-in ventilation in the roof.
I would tear them off too, but I would also remember to add some sort of ventilation to the roof system.
I would recommend soffit/ridge vent, but it's not the only system out there.

Good luck.

 

Sorry, I forgot to mention that it's about siding.
As to roof I have new one with new ventilation.