Trippy
If its only a small job, then an easy way to do this without spending on a telescopic pressure washing lance would be to buy some gaffer tape then extend a wfp without brush head or even better an aluminium telescopic unger pole, next tape your regular pressure washing lance to the end of the pole and tape the trigger on to the handle, then hey presto you can pressure wash at height
But dont forget you'll need to have someone holding the pole and lance before you crack up your machine otherwise you'll have an 18 FT pole dancing down the street
If you ask Frankie nicely he may do this for you
I've got a 20 FT unger pole you could borrow if you wanted? and will be working on Baldwin Street all day tomo on an office block if you wanted to pick it up?
Simon