By the time they've grown after flowering next year they'll have reached that height. Worthy

They have a vigorous growth pattern and expect a couple of feet this year, at least, and then once it's established it'll be a rampant plant.

They are wonderful climber that does a spectacular job at covering vertical areas.

They're NOT self clinging though, so when you say about it growing up a wall YOU will have to make it climb up it because it won't do it naturally !
Buy green plastic covered wire mesh, about 1.5-2" each square and nail this to the wall and then the clematis can climb up THAT.
The clematis climbs by winding its tendrils around THIN stems - in this case the wire - and then it'll scramble around to its hearts content and give you what you're after.

And bear in mind that montana varieties actually get about 30 feet.

Wow! 30FT eh! Well,I guess after waiting nearly 2yrs to get my awful backyard sorted out I was feeling a bit impatient and wanted it to be flowering this summer! i guess that won't happen.
I posted on here in 2009,asking for advise on how to help me create a space in my ugly backyard,well it just got uglier as I didn't have the money to spare on the outside of the house...Now,that I have i want it done pronto!
I have ordered loads of plants off Thompson and Morgan which will arrive in april,and have recently had the ground gravelled with a few stepping stones.
Will post pics of my creation when its done.
Thanks for the info on the clematis. I was actually going to get the montana for spring flowering and a purle summer one[can't remember the name] i've read that clematis are best grown with something else,any suggestions on what i could use,preferable something that is evergreen,with the clematis being deciduous i'd like something during the winter months.
THANKS!

Montana only has a short flowering period and the flowers are quite small, though the plant gets enormous. If you wanted big spring flowers have a look at Nelly Moser, who is much more restrained but has very large lovely pink flowers. There are some small flowered summer flowering blue ones that look lovely planted to grow through a yellow climbing rose - not evergreen but worth waiting for. (and you should get some flowers on both in the first summer) These have lots of little lantern shaped flowers, not the big flat ones.
Jackmanii is a very late flowering purple one that you cut down every spring and it regains its full height again by the autumn. Put a large stone over the roots if they are in the sun as they like them to be shaded. Remember that clematis that flower at different seasons have different pruning regimens.
If you want something evergreen I would grow it on a different part of the fence. Try training a pyrancantha which has white flowers in summer followed by range berries in winter. Or on a north facing fence cotoneaster horizontalis is hard to beat - easy to train, tough, self supporting and lots of red berries for the blackbird! (Not evergreen though)

The usual reason for saying clematis like to be grown with something else is simply to give the roots protection from sun by planting something in front of it - but you get the same effect by putting stones or slabs over the base anyway. There are plenty of smaller evergreens you could use if you want to plant in front though - Lavender, Santolina, Senecio (now Brachyglottis) in sun, or any of the evergreen Hebes such as H. albicans or H. pagei (check the eventual heights of any you like before buying, they vary from 9 inches to 12 feet), or Euonymus fortunei varieties for variegated leaves in winter (such as E. Emerald'n Gold).
If you don't want a large flowered hybrid for spring, check out Clematis alpina 'Frances Rivis' - a stunning beauty when in flower.

Another reason for them being grown with other things is so the other plant can be the clematis' host - providing it with something to cling to.