How do I stop rain blowing into a porch or open doorway?

Wind-driven rain does not fall vertically, which is why a shallow canopy that keeps the doorstep dry in a shower does nothing in a westerly gale. The rain arrives at an angle, wraps round the corner of the building, and rebounds off paving so the bottom of the door gets as wet as the top. Every workable fix does one of three things: intercepts the rain higher up, breaks the wind before it reaches the doorway, or gets the water away once it lands.

Safety

What you'll need

• A canopy or hood sized for the doorway (optional)
• A drip bar or weather bar and a good threshold seal
• A threshold drainage channel or ACO drain (optional)
• Exterior-grade sealant and fixings suited to the wall
• A drainage fall away from the door — a mortar or paving adjustment (optional)

Step by step

1. Watch it in a storm and see how the water actually arrives.Over the top of a shallow canopy, round the open side, or bouncing off the paving. Each has a different fix, and guessing wrong means spending money without solving it.
2. Note the direction the worst weather comes from.In most of the UK the driving rain comes from the south-west. If your door faces it, expect to need a deeper solution than a token canopy.
3. Extend the shelter over the door first.A canopy needs to project meaningfully — 600mm or more for a door on an exposed elevation — and be wider than the opening on both sides. A 300mm hood over a west-facing door is decorative.
4. Close in one or both sides.A cheek or side panel on the windward side, glazed or solid, stops the wrap-round that a canopy alone cannot. This is what turns a wet porch into a dry one on most exposed doorways.
5. Fit a drip bar above the door and a good threshold seal.A drip bar or weather bar throws water clear of the face of the door instead of letting it run down onto the threshold. Combine with a compressible threshold seal and a decent door bottom.
6. Deal with the bounce off the ground.Water hitting paving right in front of a door splashes back up the bottom 300mm. A gravel margin, a threshold channel drain, or paving that falls away from the door all break that cycle.
7. Make sure the water that lands can leave.A porch floor that falls back towards the door, or a threshold below the surrounding paving, holds water at exactly the point you are trying to keep dry. A channel drain across the threshold and a fall of about 1 in 60 away from the house fixes it.
8. Check the canopy's own drainage.A flat or lead-covered canopy needs a fall and somewhere for the water to go, otherwise it discharges as a curtain straight down in front of the door — or worse, back against the wall.
9. Consider a full storm porch if it is a permanent problem.An enclosed porch with its own outer door solves it completely, and it adds a draught lobby that reduces heat loss. Check permitted development limits — a porch under 3 square metres, under 3 metres high and more than 2 metres from a highway boundary usually does not need planning permission, but listed buildings and flats are different.
10. Do not just seal the door tighter and hope.Sealing an already-wet porch traps moisture, and a fully sealed unventilated porch grows mould on everything in it. The water has to be stopped outside or drained away, not shut in.

Tips

• An open-slatted screen or a trellis panel at the side of a doorway breaks the wind better than a solid panel does, because a solid barrier creates turbulence and downdraughts behind it.
• A porch that is enclosed needs ventilation, otherwise wet coats and boots produce condensation and mould on the inside face of the outer door. A trickle vent or a small grille solves it.
• Fitting a canopy into a cavity wall needs the right fixings and, on anything substantial, a builder. A canopy failing over a doorway is a genuine hazard, not just a repair.
• If water is getting under the door rather than blowing in, the problem is threshold level and drainage, not wind — that is a different job and a channel drain usually solves it.
• Check whether the property is listed or in a conservation area before adding a canopy or porch to the front elevation. Both change what is permitted.

Common mistakes

• Fitting a shallow decorative canopy on an exposed elevation — It intercepts almost nothing at an angle and gives the impression the problem has been dealt with. Depth and width are what matter, not the presence of a hood.
• Sealing an enclosed porch completely — Wet coats, boots and breath in an unventilated space produce condensation and mould. Enclosure needs ventilation designed in.
• Raising the paving to meet the threshold — It bridges the damp proof course and lets water into the wall, which is a far worse problem than a wet doormat. The threshold should sit above the paving with a drain if needed.
• Ignoring where the canopy's own water goes — A canopy with no fall or no outlet just delivers a concentrated stream in front of the door or back against the wall. It needs a fall and somewhere to discharge.

If it doesn't work

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