What aka says was really brought home to me when I visited the Rhododendron Species Foundation a few years ago. They were transplanting some of their largest rhododendrons. They had the roots clamped down on a shipping pallet for the move. The roots were only about 5 inches thick and didn't even extend all the way to the drip line. Here is a photo of a rhododendron that was 8 to 9 feet tall:
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It's the other way around Jenn. Oftentimes planting a rhodie near limestone foundations results in chlorosis, etc from a high alkaline soil.

I thought foundations were made of concrete.
Yes, there is lime in concrete. Very little of it leaches from the foundation. At least not enough to adversely affect the ph to the point rhododendrons suffer. Here in the NW, rhododendrons are a standard foundation shrub.
Left over mortar around a chimney is another matter.
Mike

The main ingredient in both mortar and concrete is Portland Cement which is made from limestone, CaCO3. Enough lime can leach from a foundation to effect soil pH when the foundation is relatively new. Once it has weathered for a while, the danger is slight unless excess concrete has been directly dumped into the soil near the foundation - a surprisingly common practice.

I second what aka says.

Fresh cement and mortar leach a great deal of alkalinity into the soil. Around homes that are a few years old, the pH is always much higher within a foot or two of the foundation, chimney and walkways. This goes away after a decade or two. Application of powdered sulfur is a good antidote, but is slow acting just as the lime in concrete and mortar is.

Regarding the great Pacific Northwest, there are regions near the coast where the soil has iron sulfates and is so acidic that they actually apply lime before planting rhododendrons and azaleas. They can get chlorosis that is caused by low pH. That is completely alien to those of us in the East.