Rain drip caps
An extruded aluminium section fitted horizontally above the frame head on the external face. Its projecting lip interrupts water running down the wall, forcing it to separate and fall clear instead of tracking into the gap above the leaf. Select by lip projection, material and finish; order longer than the opening width on each side.
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Frequently asked questions
How much longer than the opening should a drip cap be?
The drip cap needs to project past the frame on both sides so water running down the wall does not turn into the top corners of the opening. Measure the outside width of the frame, add the overhang per side from the drawing or site conditions, and order longer so it can be trimmed on site.
What difference does the lip projection make?
The further the lip projects from the wall, the further water falls from the gap above the leaf. On an opening with no canopy and a wall exposed to driven rain, choose a larger projection; under a deep overhang a short lip is enough.
What should I watch for when fitting a drip cap so water does not get behind it?
The cap must sit tight to the wall or frame face, with the top edge sealed with a weather-resistant sealant, or water will run down behind it. Set it level or falling slightly outward, never sloping toward the door.
Which finish should I choose for an outdoor aluminium drip cap?
Anodised or powder-coated aluminium weathers better than mill finish, especially near the coast where salt spray attacks the surface. When fixing to a steel frame, use stainless screws and avoid direct contact between aluminium and damp steel to limit galvanic corrosion.
How is a rain drip cap fastened?
The cap is normally screwed through its upstand into the frame head or the wall above it, using plastic plugs in brick or concrete. Keep screw spacing even and not too wide so wind cannot lift the edge. Place screws within the sealed zone so water cannot follow the screw shank inward.
What tools are used to cut a rain drip cap?
Aluminium caps can be cut with a fine-tooth hacksaw or a saw fitted with an aluminium-cutting blade, then deburred so the edge does not cut hands or sealant. The ends can be left open or fitted with end caps to stop water running back along the edge. In coastal areas, touch up the cut edge of anodised material with paint.
When should a rain drip cap be replaced?
Replace it when the cap has bent so its slope faces back toward the door, when the top sealant has failed and water tracks behind the cap, or when the aluminium shows pitting corrosion. Staining or algae on the frame face below the cap usually means water is still reaching the head gap. Often cleaning and resealing is enough, so inspect the cap before deciding to replace it.
Is a drip cap still needed if the door already has a door sweep with a drip lip?
Yes, because they handle different places: the head drip cap protects the top gap, while the lip on the sweep protects the bottom gap. Water running down the wall that is not stopped at the head flows down the leaf face and loads every seal below it. On outward-opening doors without a canopy, use both.
