How to fasten to a concrete block wall to hold a 20' extension ladder

I would use 1/4" diameter toggle bolts placed in the hollow areas of the concrete blocks to hold the ladder brackets. An easy way to make a 1" hole in the hollow part of the block (for the toggle bolt) is to give it about six gentle taps in exactly the same place each time with a hammer and you will get a nice round 1" hole.

You can use a good quality lag for concrete. The rail isn't long enough for a 20' ladder so i would use 2 rails (or 1cut in half). I have 2, 6" pieces, with 2 lags per piece holding a 16' ladder and I use the ladder a lot. Your extra 4' shouldn't be a problem.