Almost impossible to visualize from your description....can you provide photos? How tall do these trees need to be to provide an adequate screen? And not sure what you meant by your last statement.........the Thujas ARE evergreens :-)) Do you mean only the narrow arborvitae-type thujas? Is there a width restriction?

ditto what she said.

Sorry if I wasn't clear. From our back window we have about 25 ft of flat yard, then 5 ft sloping up at about 30 degrees. Then a fence, about 6.5 ft tall. Beyond that is another 30 ft backyard followed by a two story house. The fence blocks off about half the first floor. Double that (13 ft) and the windows looking down on us would largely disappear. Unfortunately, such a fence would be illegal.

Yes, to keep the message from becoming even more interminable I was hoping readers would understand "evergreen" in this context to mean some non-skinny variety that would have to sit at some distance from the fence as opposed to the thuja that could be right up against it and would look kind of odd anywhere else.

My original plan A was to put some birch in the middle with the thuja in the back, which should look pretty even in the dead of winter. Curious why I've never seen this. The landscaper sort of grunted and said birches don't like the clay soil here, though there are at least two on this street.

Thanks again.

One other thing, yes, there is a sort of implied width restriction because the yard is short. A wide deciduous tree is ok because one can still walk underneath it, though it is of little help in a long Ontario winter. A wide pine or fir will be there in the winter but will eat up half or more of the yard's depth.

"... birch in the middle with the thuja in the back ... Curious why I've never seen this." Because in 25' or 30' of spatial depth, there isn't room. Birch get large and eventually would produce enough shade on the front side (the side you look at) of the Thuja that it could not maintain its foliage. It would not be pretty.

Funny that ... "evergreen" always means always green. It doesn't mean "non-skinny," no matter the context.

"The landscaper sort of grunted and said birches don't like the clay soil here..." He is probably short on a source at the moment.

Forgive the general dislike of written descriptions without pictures. Usually, they are woefully inadequate and often the pictures make evident features or conditions that were thought unimportant by the author. Your second attempt isn't too bad, but a picture would make what you're trying to describe, clear and obvious, and greatly improve your chances of getting better help. Without a picture, I'd be inclined to say go with the Thuja idea. With a picture, I might offer an entirely different suggestion. Pictures spur thought.

Thanks for the advice on the birch. The ones I see across the street don't seem that big, but then they are not walk-under trees either.

Any thoughts on putting thuja up and just past a 2ft high wall? The wall would be about 5ft from the back fence. Plant closer to the fence to give the roots room or closer to the wall for the tree/shrub, or split the difference?

Sorry about the lack of pictures. Haven't developed this skill yet, though will work on it.

With only 5' depth available, plant closer to fence or split the difference.

I guess whether or not a wall makes sense depends how many arbs and how big you want them. I'd do the math - going from 6-8' arbs to 8-10' is a difference of $225/ea, multiplied by the qty involved. A retaining wall can run anywhere from $30-100+ per square foot of face. I'd probably forego the wall and plant monster arbs, especially since you'd be planting a big sail right behind a wall.