We have bay window that has sagged enough that that windows are out of square and no longer open or align properly to get a good seal. As such, they are drafty in the winter and we can't open them in the spring or fall to enjoy.
It seems the options for leveling a bay window are to suspend it using cables from the top, or build support from underneath. The cable method doesn't seem to be a good option because the roof of the bay window is basically flat and metal. Here are the steps I'm planning on taking with questions.
- Lay plywood down on the ground and using a floor car jack, slowly raise the bay to slightly overcorrect the level issue. This will allow some settling when adding the supports. Questions: will a car jack work here?
- Using pressure treated 2x4s, build 2 knee braces.
. Questions: will 2x4s look tacky? My plan is to paint them white - Attach knee brace to cinder block foundation and the bottom frame of the bay window. Questions: how should I attach the knee brace to the foundation? Tapcon screws? Is this structurally sound? What type of fasteners should I use for the knee brace joints?
Here is a view the underside of the bay window: 
Final questions: is this all a bad idea? Should I have supports in the ground instead? Or maybe the whole bay window just needs to be replaced? Any and all advice would be appreciated.
Best Answer
I cringe when I see this type of construction. How good are you at mixing concrete? I'd be digging out that area under the bay window, compacting it, adding a few reinforcing rods into the existing foundation, a little framing and pour a 6" slab/footer. Then use your jacks to slowly raise or even over raise the window, cinderblock and morter it in and cover with a coat of stucco. Don't forget to extend the vent with a prefab from your home store.