Fit a timber weatherboard above your external door’s bottom edge to throw rainwater clear and stop it rotting the frame.
WB-01Buy the right weatherboard and screwsMeasure your door thickness (usually 35mm or 44mm) and buy a weatherboard moulding to match — most timber merchants stock pre-machined profiles with the drip groove already cut in. Choose a timber that's already treated for outdoor use, such as redwood or hardwood. Buy stainless steel or brass screws, not plain steel ones, because steel screws rust and streak the paintwork.
WB-02Take the door off its hingesGet a helper to support the door while you lift it clear of the hinges, or tap out the hinge pins if it's that type. Lay the door flat across two trestles or a workbench, protected with an old blanket or dust sheet so the face doesn't get scratched. Working flat makes cutting and fixing far easier and more accurate.
WB-03Mark the fitting line on the doorMeasure up from the bottom edge of the door — typically 150mm to 175mm, but check the fitting instructions that came with your weatherboard. Draw a level line right across the face of the door using a straight edge, making sure it's parallel to the bottom edge, not just a set distance up at each side.
WB-04Cut the weatherboard to lengthMeasure the full width of the door and transfer that measurement to the weatherboard. Cut it square so the ends finish flush with the edges of the door. Sand the cut ends smooth and check the length against the door before fixing anything.
WB-05Cut end returns to shed waterIf your weatherboard isn't already machined with end returns, cut a small 45° angle on the underside of each end so rainwater drips clear of the door edges instead of running down onto the frame below. This is a small detail but it stops water tracking sideways into the door's end grain.
WB-06Run a bead of sealant along the fitting lineApply a continuous bead of exterior frame sealant along the marked line on the door face. This beds the weatherboard down and stops water getting behind it and into the door. Don't skip this step — it's the main thing stopping damp getting in behind the board.
WB-07Fix the weatherboard to the doorSit the weatherboard on the sealant line and pre-drill pilot holes through it at roughly 300mm centres, countersinking each one so the screw head sits below the surface. Screw into the door face, working along the length and checking it stays straight and tight to the sealant as you go. Don't overtighten — you can crush the timber or squeeze all the sealant out.
WB-08Seal the screw heads and cut endsFill the countersunk screw holes with exterior wood filler and let it go off fully. Prime any bare cut end grain and the filled holes — end grain soaks up water fastest, so this is the part most likely to rot if you skip it. Leave everything to dry before handling.
WB-09Re-hang the door and check clearanceWith your helper, lift the door back onto its hinges and check it swings freely. Close it fully and check the new weatherboard doesn't catch on the frame or threshold — if it does, you may need to plane a few millimetres off the bottom edge of the door. Check there's a small gap, around 5mm to 10mm, between the weatherboard and the threshold below so it can throw water clear without dragging.
WB-10Paint or treat the whole doorOnce any filler and primer are fully dry, apply an exterior undercoat and topcoat, or an exterior wood stain, to match the rest of the door. Pay extra attention to the new weatherboard, the screw heads, and any bare timber. Follow the drying times on the tin before closing the door fully or letting it get wet.
WB-11Tidy up and do a final checkSweep up sawdust and offcuts and wipe down your work area. Open and close the door a few times to make sure it operates smoothly with the new weatherboard fitted. Check back after the next spell of rain to make sure water is running clear of the frame and threshold, not pooling or tracking back underneath.
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