The upstand is the slightly raised edge along the back of an external window sill, under the window frame. The Dutch name for it is klik. Its job is to shed water: rain landing on the sill or splashing back off the facade is held back and cannot run under the frame or sideways along the reveal into the wall.
External sills are therefore supplied both flat and with an upstand. The upstand is a couple of centimetres high; what is right in a given situation depends on where the frame sits relative to the brickwork. Sizes differ per manufacturer, so check the details with the supplier.
Where it is used
- Under external windows — the standard arrangement under windows in a masonry facade
- In renovation — when a frame is replaced and the existing level does not work out, a sill with a taller upstand or none at all can resolve the junction
- Behind cladding — where water can get behind the facade finish, something else has to take over that shedding function
Points to watch
- Never stand the frame straight on the sill — timber standing in water rots. There should be a gap, ventilation and a seal; spacers or sill clips keep the frame timber off the masonry
- Projection — the sill has to project far enough beyond the face of the wall (in practice at least around 4 to 5 cm) and have a drip groove or a chamfered underside, otherwise dirt streaks run down the facade
- Sealant is not a roof — the sealant joint between frame and sill is a seal, not a water bar; if the upstand fails to do its job, the sealant will not save it
- Fall — the sill must be laid to fall outwards so that water runs off
Related terms
- Drip sill
- Sill
- Window frame
- Reveal
- Water barrier
- Drip mould
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