the joint in one embodiment the caulk used for the caulk bead 452 is structural grade silicone at the portion of the joint nearest the exterior side of the storefront a gap of set height 453 is provided which is designed to match the warranty requirements of the standard window sealants used in the industry in the embodiment shown in fig4 this gap has a height of u215c inches a water dam 411 may be provided at the interior side of the caulk bead 452 as a further moisture barrier in the event that water is able to infiltrate through to the interior side of the caulk bead 452 the water dam 411 also provides a stop allowing for easy installation of the window and sill can 450 once the fenestration cap 400 is in place in a window opening an unskilled laborer would easily be able to install the sill can 450 and related components to provide a finished storefront by lifting the window assembly up and into the opening within the fenestration cap assembly placing the interior edge of the sill can 450 firmly against the water dam 411 as such no measuring is required for the installation of the window assembly itself when the fenestration cap 400 has been used to frame the window opening ahead of time furthermore even if despite all the precautions built into the design of the fenestration cap 400 water is able fully infiltrate the joint in the area of the caulk bead 452 and pass over the water dam 411 the fenestration cap 400 fully spans the width of the window opening in which it is.