I'm renovating our house and want to enlarge the window that is currently in this room. At minimum this would mean putting in a window that is taller, but also possibly wider. Given the way that it's framed how feasible is this to do on my own? I'm reasonably handy but have not done any window work so far.
The wall itself is an outdoor wall, single story, only bears the weight from the flat roof above. We're in an area that can get 8-10" of snow in the winter. Other things to consider?
This looks like DIYer job to begin with. The first glaring problem is no jack studs holding up the header or sill plate for the window. The sill plate for the window looks piecemeal as do the cripples for the sill plate. The double top plate seems to vanish into a single one toward the right of the window. This should be fixed. Get a book on framing to become more familiar with how to do it. I'd think about getting a floor jack or two and supporting the roof and removing the existing window and framing and doing it right.
Windows and doors typically have a king stud & jack stud (trimmer) on each side. The king stud is full height, from the bottom plate to the top plate. The jack stud goes from the bottom plate to the header and the header sits atop this stud.
If you want a taller window you can simply move the header up and the sill down. This will require cutting the cripples to accommodate the new size. As mentioned in the comments, there should be a jack stud supporting the header. I would add one since you're already there.
If you want a wider and taller window you have a bit more work on your hands. Start by supporting the roof section temporarily. I would use some 3/4 plywood on the floor spread out over a couple joist bays. This will support your temp posts, then get some 4x4s and do the following.:
Hold one 4x4 up to the ceiling to act as a temporary beam and attach it to those furring strips with some 3" screws, you'll have to drive them at an angle through the side of the 4x4, then measure the posts, cut them an ⅛ or so big, and wedge them it, secure with a couple screws to the temp beam. You want this whole setup to be wider than your new window.
Now that you have everything supported, you can get to work. Take the window out and get it out of your way, remove the king studs and layout your new window rough opening on the bottom plate. Cut your king and jack studs, header and install. You're likely going to have to cut any nails penetrating the sheathing where you removed any framing members. Nail in your new framing members and cut the sheathing to the new rough opening.
When you install the new window, make sure to center it in the opening. Nail/screw the sides and bottom, I typically don't put any fasteners in the top, it allows the header to move without pinching the window which can cause opening issues.
