Should I put a slip sheet between the bottom of masonry walls and the top of metal flashings or between the bottom of metal flashings and the top of shelf angles in order to accommodate differential movements resulting from temperature changes?
Typically, slip sheets are not installed. Although the flashings and shelf angles have higher thermal expansion coefficients than the masonry, they go through smaller temperature swings because the shelf angles are attached to the building structure without any thermal break. This tends to keep them warmer in the winter and cooler in the summer. Separator sheets are often used between metal flashings and galvanized shelf angles to prevent galvanic corrosion. These may also serve as slip sheets but this is not their purpose. If differential expansion does occur, damage is unlikely to result from differential movement between these elements. There is very little bond, if any, between the masonry and the flashing surface.