Window sills see a lot of water. This is largely because glass is very waterproof, so all the rain that hits a window will end up on the sill. All that water needs to be directed outwards. For that to happen, first sills need to be proper pitched, especially if windows are set deeper into walls to optimize Psi/thermal bridge values (Linear Thermal Conductivity in Btu/hr*ft*F or W/mK). Then, to assure that water is direct outwards, ProClima developed EXTOSEAL ENCORS, a very stretchy self-sealing sill tape with acrylic-modified butyl adhesive which works in winter down to -4°F. It can be applied to the exterior of the window frame (European window installation style) with the 3/4″ release strip – and up both sides of the opening for a continuous, one piece sill. It can also be folded down onto the face of the wall WRB – as shown in the video below – though preferably by no more than an inch so as not to block any outward drying potential.
Beyond sills, EXTOSEAL ENCORS is an extremely versatile product and is useful for many other waterproofing and airtightness applications. With its stretchiness, conformability and superb adhesion, it performs reliably in many demanding situations. For the difficult junctions pictured below, a reliable air seal was achieved with just one piece of tape. In the picture at left, narrow pieces of ENCORS were used on the top and bottom of a joist. On the right, a very awkward corner was air tightened at the spot where INTELLO (at the top of a masonry wall), a roof joist and a knee wall meet.