I wish I could help you more, but I haven't got the expertise. It sounds to me like you've thought this out quite well. I do have a question though: why are you concerned about the hornbeam when it's leafless? Usually at that time of year we spent less time outside in the yard anyway, so privacy isn't really an issue. At the same time, the winter sun can get through to the house and do its bit toward reducing heating bills. That's one of the great advantages of deciduous trees.

I rather like the Thuja. In fact I planted a long row of Emerald Green at church 3 years ago. They are hiding the ugly chain link fence very well. They are green all year and narrow enough for what you need. You'll have to search for the ones with a single trunk or be consciencious in tying them up before winter hits, because they bend down under heavy snowfall.

Good luck with your decision. :-)

Thanks to both of you, pitimpinai and janetr, for your input. Janet, to answer your question, I have concerns about losing the leaves because of house privacy (not just yard privacy). On the first floor, our breakfast room, which opens to the kitchen and family room, is right next to the garden. We don't have window treatments there and without trees right now, we feel really exposed to the apartment buildings behind us. I think your point though about winter sun is a good one.

Pitimpinai, have your planted the Thuja Green Giants or just the Emerald Greens? How tall were the Emerald Greens when you planted them and how tall are they now?

Thanks!

I grew up in an 3-story English Tudor-style house with a similar yard (my mother is still there), although the back yard is turned ~90 from yours. Ie., it is ~30ft wide by ~50ft deep. Because the house is at the bottom of a hill and the houses from the intersecting street have their rear yards extending perpendicular (crosswise) but on a higher grade (about 7ft - 8ft above my mom's grade), anyone in the closer houses can look down into the yard. The people who owned the house before us installed an aluminum/wrought iron covered patio connected to the back of the house and that helped some for privacy in the back, from anyone looking down from "above". But eventually that had to supplemented. What's currently at the rear of the yard against an 8ft retaining wall, are a 40' Eastern white pine and a 40' Norway Spruce - one in each corner. The spread of both trees covers the width of the yard (without imposing on the center). The trees were eventually limbed up to about 12' above the ground and the remaining branches droop down to near the top of the wall to form a wall of conifer branches. But it took a bit of time for them to get there (30-some years from young 4' trees). ;-) But before they reached that size, my mother had Blaze climbing roses there to supplement the existing old New Dawn climbers left by the previous owners.

My concern for that size yard is your considering a maple. Except for maybe the Japanese maples (and even those eventually grow over time to have a good-sized canopy depending on the variety) or perhaps a dwarf red maple, the maples themselves tend to quickly outgrow a small space. After almost 40 years of my mother dealing with her neighbor's Norway maple trees, the new owner who bought the neighboring house finally removed the largest - an 80-some year old one that was in the center of their yard (which took the landscape guys 3 days to take down when they found its canopy easily 100 ft. wide). They also removed most of that tree's half dozen 10 - 20 year old "seedlings" (that themselves were 40 footers). This all happened last week to my sheer amazement. Basically over the years, that yard had become a forest of these massive trees that were WAY too large to be in a typical city lot. Nothing could grow under them and they became a nuisance with the yellow pollen when blooming, the seed wings, the continual threat of lightning strikes and constant fear of tree trunk-sized branches that could hit the house. A large branch had already cracked off a couple years ago and damaged the chainlink fence between the properties. The trees became a bridge for the squirrels and racoons to the roof and OMG the leaves that piled half a foot thick in my mother's yard.

I've seen Autumn Blaze in action and it is a beautiful tree in fall but IMHO, it would be the kind that might be planted in one of my sister's yards (1/3 acre) rather than my mom's. Granted - it's not a Norway maple but it can become as large as one.

As an alternate to the thuja, you could consider an Easter Red cedar (Juniperus virginiana) which has a columnar to pyramidal habit. Along the back, just as a what-the-heck since I've seen them planted for similar reasons, is an upright english oak (Quercus robur 'Fastigiata'). This particular one is columnar and somewhat slow growing but is also narrow. There are a couple planted along the back of my apt. building, probably when the building was built ~1960 and they are now about 7 stories high. I've seen a few downtown here as street trees in the historic part of the city.

Another alternate might be a thornless locust (honey or black). There are some that are slow growing, have a beautiful shape, and produce thin compound leaves that don't mat like the larger hardwood leaves.

Just some suggestions and thoughts...