experimentation has also shown that the best results are obtained if the fixed rail 42 is vented using the end caps 46 as illustrated though other venting arrangements may achieve the same results the ventilating end caps 46 permit water to drain through the valve assembly 10 even under high wind conditions the valve assembly 10 and the ventilating end caps 46 comprise the only components of the drainage system for sliding closure assemblies in accordance with the invention fig3 shows a horizontal cross sectional view of the patio door assembly 30 with the fixed panel 40 in its normal position the construction of such door assemblies is well known in the art fig4 shows a vertical cross sectional view of the patio door assembly 30 taken along lines iv iv of fig2 as explained above the patio door assembly 30 includes a sill 32 which is generally a solid construction for durability the sill 32 typically includes a wooden core 48 which is covered on a top surface by a sill plate 50 typically an extruded thermoplastic which may include an integral track 38 for supporting the sliding panel 36 a front edge of the core 48 is typically protected by an aluminum threshold 52 which generally includes an integral track 54 for slidably supporting the screen door 44 the fixed panel 40 is supported by a fixed rail 42 which comprises a hollow extrusion that may include one or more chambers as shown in fig4 the fixed rail 42 has an inner wall face 58 and an outer wall face 60 in equipping the patio door assembly 30 with a drainage system in accordance with the invention drain orifices 56 are cut.