I know this topic has been covered before, most comprehensively by Big-All, but I need to put my mind at rest!
I am about to put an inner stud wall and new pitched roof on an old concrete section garage. All I need to decide is 3x2 or 4x2 studding and 18" or 2ft. centers, by the way the roof will only be ply and felt shingles.
Your expert opinions would be gratefully appreciated

Hi Paul,

Is your garage going to be habitable? If so, use 4X2 (to allow for insulation) If it is just a work space, use 3X2. I'm hoping your stud wall is not weight supporting. 600mm centres will be fine.

Simon

Its literally going to be a worshop, not habitable, the studwork is going to take the weight of the pitched roof

Hi Paul,

I'm guessing the studwork runs round the edge of the building?

S

Yep, basically as it stands now I have a concrete sectional garage, you know the 12" sections all bolted together, the plan is to remove the roof, stud the inside and build a pitched roof off the top of the studwork overlapping the concrete outer wall, so I will end up with a shed within a concrete wall.

Hi Paul,

I would go for 4X2 at 400mm centres. Also, add an extra wall plate i.e., double up on the top timber horizontally so that you have 2 nos 4X2's at the top. I would also mechanically fix the timber to the concrete sections. I would also fix a wall plate to the top of the concrete sections to take some of the weight.
Will it be a hipped roof? Is the main garage door opening remaining the same? If so, you will need to have a larger timber to span the opening, say 2 nos 6X2's bolted together.

Simon