How to extend 5/8" window jamb?

Question

The window I just received in special order came with a 5/8" jamb. I'm really upset at that awkward dimension because it makes it difficult to extend it with regular 1xX lumber (actual thickness 3/4").

How should I go about extending it assuming I don't have access to a table planer? I'm thinking to use 1xX and then fill the recession on the window side using wood filler. It's not elegant. Do you have any better ideas?

As a bonus, can anybody actually justify the nonstandard choice of lumber on the factory side? I'm very frustrated.

Answer 1

When I do jamb extensions, I'm butting tight against the existing window frame, but nailing through shims into the rough framing. I offset the jamb extension by about 3/16", and caulk that reveal. In that scenario, the only time 5/8" material in the window frame would be a problem was if the window was tight to any or all of the framing. If that was the case, I'd get 1/2" actual stock (good lumberyard!) and be happy with a 1/8" reveal.

As far as justification for 5/8" stock... well, we seem to be in a race to the bottom with building materials. Anyone that can squeeze a penny here or there makes more money. (The one that made me laugh/cry was the entry door that had hinges double-thick mortised into the jamb and flush mounted on the door. Ta-dah! One less step in the manufacturing process, and it probably only looks terrible to people like me.)

Answer 2

Just a couple of other options I've exercised a number of times in even rabbeting casings, though I do agree largely with A.D.

A planer is great, but you can uniformly plane 1x down, a little tediously, with either a Circular Saw or a Router very successfully. It's definitely worth it for 1 window & you can even customize it if there's any deflection in the window opening's framing or for nail heads or knots that won't pound in or can't without protruding though an adjoining window's jamb.