Abstract: Methods and apparatus for sealing perforations in windows, curtain wall and other building fixtures are disclosed. The present invention enables the construction of building exteriors impervious to water leakage through holes in sills and other building exterior components. a molded plastic cap [10] is secured around each exterior hole [20] and fastener [16,18] with an adhesive [22]. The cap prevents water from leaking through the exterior hole into the building interior while allowing sills and exterior sections to move in response to thermal, seismic and other mecahnical changes. By not coming into contact with the fastener [16,18] and hole [20], the seal [10] avoids any possible contamination and chemical degradation from the fastener materials.