A parapet wall is the portion of a wall that extends above the roof. Because parapet walls have two exposed surfaces, they can suffer serious problems. Both sides of the wall are subjected to temperature swings and rain. As a result, parapet walls are more susceptible to displacement, cracking, efflorescence, and spalling. COPING The top of a parapet wall is the most vulnerable area. Developing an effective detail here helps eliminate or minimize most moisture related problems. Choosing an appropriate cap is the first step in doing this. A coping of similar material to the parapet is strongly recommended. This would include: limestone, precast concrete, hard-fired clay, or terra-cotta. Copings can be cast and formed into a variety of shapes, but they must all possess adequate pitch, sufficient projections and continuous drips. FLASHING Most copings are susceptible to moisture penetration where the individual sections butt (at head joints). To prevent moisture from entering the wall from the top, install a continuous through-wall flashing membrane within the mortar bed immediately beneath the coping. JOINTS To allow movement due to thermal expansion, at one end of every coping section install a soft joint. Also, a vertical expansion joint should pass completely through the parapet wall at 30-foot intervals.