ISO narrow/columnar tree beside a walkway (want to avoid surface roots) max 6' width

Can anyone suggestion a narrow/columnar tree to plant beside a walkway?
We're trying to provide some screening/privacy from a neighbour but the max width is about 4-6'.
It's also near a stone patio and walkway so want to avoid anything with potential surface root issues.

Zone 8 (Vancouver)

 

'Smaragd' arborvitae has been very popular and much used. Dense, emerald green and narrow.

 

The problem with conifers is that they do have lots of surface roots. What our strata did in a similar situation was to build a stainless steel wire trellis and plant evergreen clematis. It took a bit of care (mostly tucking growing shoots back into the area we wanted to cover) but grew quickly and had year-round interest. We could attach the trellis to a fence because it was inside our complex, but a freestanding trellis would not be hard. Just make the trellis very sturdy. You don't want to have to do this twice!

 

What's typical is for the evergreen clematis (and other climbers) to be placed on frames that are way too small for it. Also there is a tendency not to keep up with the pruning and training that is required for climbing plants to fan out onto surfaces intended to be evenly furnished, instead allowing them to quickly grow to the top of the support and bunch up there. In addition the clematis specifically accumulates masses of dead leaves that need to be cut away if an attractive effect is to be maintained.

There is a hospital in Everett, WA that has a tower with a trellis on one side that goes all the way to the top of the building or nearly so. Evergreen clematis planted at the bottom of this frame had reached the uppermost part when I first noticed the scheme a few years ago - one print manual I have here says this plant grows as much as 6 m high but the Everett planting must be at least triple that height.

 

Presumably this? That was the highest I could see in a quick look on google street view!

Edit: with the wonders of the 3D mapping on google earth, the street level at this location is 40 m, the top of the trellis at 52 m, so the Clematis there is 12 m high.

 

Right hospital but it doesn't really seem like the same building in this shot. If so, this would of course explain why the climbers in the picture are shorter than I described.

 

Thanks! Yep, google doesn't give views of all of the walls, there could easily be others.

 

Went by the Everett site yesterday, the east-facing wall of the parking garage where I saw the very tall evergreen clematis in the past now only has sections of dead foliage going part way up with new growth coming from low down. However the north-facing end of the building, which I had not looked at before has still intact examples reaching about 50' high.

I used a Nandina about 6' tall growing in the same bed to judge the height of the clematis, as well as comparison with the likely combined heights of the different floors of the garage. Whatever the exact heights of these particular examples of the species the point remains that this tree-climbing species wants to grow tall, is therefore not well suited to low supports or small spaces.