I want to plant pear trees I've grafted onto callery (Bradford flowering pear) and P betulifolia rootstock near a wall atop a robust 2 x 2 x 60' foundation.

I know some tree's roots are brutal to a foundation and others are far more forgiving. 

Any thoughts on the aggressiveness/destructiveness of pears roots, particularly Cleveland/Bradford flowering pears?  How close is too close?

BTW, I did not locate any OHxF 51 for rootstock as mentioned on my post here:  http://figs4funforum.websitetoolbox.com/post/off-topic-looking-for-pear-cuttingsrootstock-ohxf-51-7858514?pid=1290485080

It did not come with my order from the usda, and none of their pears are available due to "pathogen" problem.  Been that way for several months now. 

https://npgsweb.ars-grin.gov/gringlobal/accessiondetail.aspx?1436305

Anyone in the know here aware of what the problem is, and whether their specimens are forever quarantined?

I keep reading that tree roots destroying foundations is one of those myths that just won't die.  Except in very particular circumstances, a foundation in good order is in no danger.  What can happen is tree roots entering leaking pipes and cracks in leaking, damaged foundations (willows are, apparently, particularly bad for clogging pipes).  So if your foundation is crumbling, don't plant a tree nearby.

The myth is admittedly so pervasive that it took me a while to start believing it was a myth.  But when I was asked "Just how many basements have you seen with roots growing out from the cement foundation?" it occurred to me that I'd never once seen anything that in my life.

Still, if you're really worried for the foundation of your house, don't ask the internet.  Ask an arborist.

arborist, shmarborist.  This is Figs4fun, more (fig) knowledge than any arborist could have. 

Many here are more diversified to boot!

Your point is well taken, though,  The interwebs have led me wrong before. . .

Fortunately, It isn't my house foundation, just the new 6' wall.  The foundation is remarkably robust.  Dudes dug a 60' long 2x2' trench by hand!

My reading (on the internet. . . ) suggests that Bradford pear roots are on the less invasive side, with most problems to plumbing, as you said, and only indirectly to the foundation by way of drying out the soil, causing it to contract. 

My wall is in a low point with drain holes along its length.  Here in south Louisiana, the soil there is rarely wanting for moisture.  In fact, the trees will need to be planted in raised beds using railroad ties!

I think I'm going to go for it, planting about 3-4' from the wall, on which they will be espaliered

I can't plant until the late fall, so any other advice in the meantime is appreciated!

Hi,
I have pear trees. If like me, you keep them trimmed under 7', you'll need to plant them 4' from the wall.
If you plant closer, the trees will rub against the wall and get damaged (stems and fruits) and making some damage to the surface of the wall.
You could plant closer but when the tree is older, you'll find that it is too close to the wall.
My pear trees have a 4'/5' diameter circle foot print - but I keep them trimmed. One of the strains especially could reach 12'+ of height if not trimmed.

As for the foundations, my pear trees have roots are go deep (I never hit them while shoveling around) ) and don't stay shallow - so IMO, you're safe with a 4' distance. You could use 6' just to be a bit more relax .