What is a weathered bottom rail (weldorpel)?
A weathered bottom rail, in Dutch “weldorpel”, is the bottom rail of an inward-opening window sash or external door that is made thicker, projects outwards and has a drip groove on its underside. Thanks to this shape, rainwater running down the glass and door is thrown clear to the outside instead of creeping under the door into the building.
Why on inward-opening doors and windows?
On an inward-opening door or window, the joint between the leaf and the frame sill is exposed on the outside. Wind and rain drive water straight into that joint. The weathered bottom rail therefore projects over the sill and acts as a small canopy.
Construction
- Thickened section: the rail is deeper than the rest of the leaf and projects outwards.
- Drip groove (throat): a groove on the underside, so water drips off the edge instead of running back.
- Weathering: the top surface slopes outwards.
- Weather bar: an aluminium or plastic water bar is often fitted to the frame sill, with the weathered bottom rail closing over it.
Common mistakes and maintenance
- Blocked drip groove: paint, dirt or sealant in the groove makes it useless. Keep it clear when painting.
- Unprotected end grain: the ends of the rail are prone to wet rot; seal and paint them well.
- Underside left bare: this is the face that stays wet longest, so always paint it.
- Too little clearance: a rail that scrapes the sill damages the paint. Adjust the hinges if the door drops.
Related terms
- Door sill
- Drip sill
- Drip groove
- Window sill
- Weatherboard
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.