I got lucky with one of my diagonal braces, having forgotten the 12′ 2X6 that’s been my “temporary” threshold for 10 years that had to come off to make room for the new porch flooring. It’s rather weathered for any other use but it makes a fine underfloor brace. I still had to use a 2X4 on the other side, but the corners are nicely braced with 3/4″ plywood.
I was very interested/apprehensive to see if the porch would hold its level when I backed up the Jeep…
And initially, at least, it does! If it will just hold this for a couple of weeks: Once the tops of the middle and two end 4X4s are tied to the roof, it won’t go anywhere. Actually it occurred to me halfway through the morning that most of this work wasn’t really needed, since I could have waited till I was ready to tie the uprights to the roof joists and then forced everything back to square. But whatever: It’s been a learning experience. Next time I’ll remember diagonal braces.
Now I’m going to have some lunch and a cup of tea, and get to work on the floor.
“Once the tops of the middle and two end 4X4s are tied to the roof, it won’t go anywhere.”
I initially questioned the above statement, but on further reflection: Assuming that your new roof consists of joists tied together with plywood decking under the roofing material, your roof will have the equivalent of an infinite number of cross braces, So yes, it should do a good job of holding the tops of your 4X4s from moving sideways.