Download this image to work on
Make a new layer for the wall wash
Make an elliptical selection …
Hold down the Alt key with the rectangle selection too and remove the bottom half …
Set up a white to transparent gradient …
and draw the gradient from top to bottom of the selection …
Deselect (Ctrl D)
Filter/Gaussian blur …
Ctrl T (Edit/Free Transform) scale and move into position …
Right click distort …
Pull corners to align to converging lines …
In this case it is easy, just line up with the bricks:
Hit Enter …
Set wall wash layer to overlay, or, turn down opacity:
