Posted: 06/01/2014 at 16:02
If you want to save on space, try attaching some roofing or sound insulation blocks to your fence and then put another fence or trellis panels in front of that. That would be about 6 to 8 inches thick in total. We've recently had a new roof done and they took off the old tiles then attached slabs of insulation about 10cms thick and 1m20 by 4m on the outside of the beams and framework then put the new tiles on that.
It would be quick and easy and you could always top it with decorative planks of some sort to finish it and protect the insulation from rain.
However sound will rise above the fence so you may want to consider taller posts for the inside fence so you can attach trellis or wires and train climbers up there or support a hedge on stilts to give you privacy from the road - and any passing double deckers - as well as cut down noise.
The picture was taken at Coloma rose garden in Belgium where such features are a common solution to providing privacy whilst being economical on space.