I wouldn't dream of placing that plant in that location. A northern exposure in NJ doesn't sound like it would have enough light for a Magnolia grandiflora, and a 4' wide bed is pretty small for a 20' wide tree (although, technically, I guess it could be tortured trained to "fit". Then there's the foundation/structural problems. I've seen foundations pushed out from under houses by magnolias planted much further out than that from houses.

I don't understand the part about this tree becoming a "viney type plant".

"Viney type plant?" Might be talking about espalier work? A very slow process on southern magnolia, methinks. I agree that a north facing location is probably not best - I have always believed that a southeast corner location in zone 6 was best because it gives some winter wind protection and is generally the warmest location for magnolia in the winter.
hortster

Didn't mean a vine per se...just one that kind of grows along a structure and doesn't protrude very far outward. I was on two garden tours that had done it this way in my town and it looked great. But it may be what Horster said - more of an "espalier"...although it didn't appear that deliberate. It's a tough spot to grow anything really...especially something with some winter interest & one that can be pulled away when house needs painting. I'm not crazy about regular ivy in that spot and and I am too chicken to put Parthenocissus there. So I guess I'll just stick to window boxes and decorative trellises. Thanks for your help.

Trees like southern magnolias cannot be turned in vines. Vines however can be turned into trees an example would be wisteria. You mentioned that you always see southern magnolias up agaist houses. This is because many homes leak heat during the winter raising the temperature around the foundation by a few degrees giving extra protection to the tree. The home itself also acts like a barrier to high winds. If you want a southern magnolia i would recommend the Pocono cultivar. Its smaller, is more cold hardy, it flowers more, and doesnt get winter burn. I have seen the origninal specimen and it looks quite nice. You can order this tree from rarefinds nursery.

I think "viney type plant" was probably a confusing description to use..I know trees cannot be vines but these trees were just growing pretty flatly against the house (like a vine does) and covered a large area quite nicely. In any case, I will look into the Pocono cultivar - sounds very interesting! I appreciate your help!

'Pocono' is a little more cold hardy than many other cultivars, but the rest of the disadvantages/problems still exist. If you plant one, remember me in a few years when you really wish you hadn't planted it.....Or, if it works out, come back and tell us (right after you've repainted your house through the limbs).