There is a product called Bio-Barrier which uses a system of controlled release antiroot chemical (for want of a better term)which is attached to a flexible sheet in little nodules. This is pretty widely used under driveways and sidewalks. It does work (for how long is another matter) but requires a lot of excavation and careful placement. I'm not at all familiar with the trees you want to use, but anything with roots this close to a foundation is courting future difficulties in my opinion. Bio-Barrier or something like it in a trench on the foundation side may indeed work, but it would involve a lot of digging and considerable expense. Digging right next to any foundation is never a terribly good idea anyway.

Do you prefer evergreen, like a Holly (such as Oakleaf Holly) or deciduous (like a Bloodgood Japanese Maple)? About how close is 'next' to your house? A lot of trees need to be planted a good deal further away than folks originally plan, so you might want a 'Fireglow' Japanese Maple instead of a Bloodgood, for example. Do you like narrow/columnar trees like a Skyrocket Juniper or Emerald Green Arborvitae, or a somewhat broader-based pyramidal tree (such as Boulevard False Cypress), or do you like the rounded crowns seen with some mature maple trees like sugar maple? By 'ornamental' do you mean flowers in Spring (e.g.: redbud, dogwood), colorful foliage (e.g.: Thundercloud purple plum, I believe, or some Japanese Maples such as Fireglow or Crimson Queen) or perhaps even peeling bark (e.g.: Paperbark Maple)? I know you mentioned 'that flowers,' but be mindful many plants that are highly ornamental when they flower do so briefly, and aren't nearly so impressive most of the year. Richard.

Go to your other post for the answer.

trees are basically full sun ... but.. as along as they get some sun ... most will live ... perhaps they wont be as vigorous as you like.. but they arent going to die.. from reduced sun .. and keep in mind.. there are other variables planting near huge old trees .. like water competition.. etc ... you might want to think about when the ash will have to be removed ... and plan on what you plant.. being replacements ... in tree time.. this would be planning ahead ... you confuse me a bit ... you talk of JMaples .. and then talk about red maples ... to my ear.. and im too lazy to spend time edumacating myself this morning .... you are talking about 2 wildly divergent trees .. to my mind.. warped as it is.. one is a small ornamental foo foo tree {the JM].. and the other is a largish maple [red maples.]... you will get much further along with your analysis if you start using the latin names ... to insure you and everyone else are talking about the same thing .. not only here.. but if you move into discussing such in the trade ... now go plant some trees... link to a good primer below ... ken note proper timing.. and proper watering: https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub