Is the ground level too high against my house wall?

Ground level against a house only ever goes one way: up. A new path is laid over the old one, a drive is resurfaced rather than dug out, a border is topped with compost every spring, a patio is raised to meet a new door threshold. Each addition is small. Thirty years of them buries a barrier that was correctly built.

Safety

What you'll need

• Spade
• Tape measure
• Barrow and a means of disposing of spoil
• Clean 10 to 20mm gravel
• Bolster and lump hammer for lifting paving (optional)

Step by step

1. Find and mark the damp proof course line on each elevation.Chalk it. You need a datum before you dig, and it is surprisingly easy to lose track of once the ground is disturbed.
2. Measure the shortfall.Measure down from the marked line to the ground at several points along each wall. Note the worst point — the ground is rarely level and one corner is usually much worse than the rest.
3. Check where services enter.Gas and water usually come in through the wall near the meter, drains run to gullies and inspection chambers, and an electricity supply may run in a duct. Locate them all before a spade goes in the ground.
4. Take out a margin, not a trench.A strip roughly 200 to 300mm wide against the wall, dug down so its base is at least 150mm below the barrier. That is enough for the wall to breathe without going anywhere near the foundation.
5. Stop if you reach the footing.If you expose the top of a concrete footing or the wall visibly steps out, stop digging down and get advice. Undermining a foundation to cure damp is a considerably worse problem than the damp.
6. Fill the margin with clean gravel.Not soil, not sand, not mortar. Loose gravel lets splashing rain drain immediately instead of standing against the brickwork, and it stops the margin filling back up with leaf litter and weeds.
7. Restore the fall away from the building.Any path or paving next to the wall should fall away from it, not towards it. Water pooling against a wall does far more damage than the height alone.
8. Re-expose any airbricks.Buried airbricks mean an unventilated underfloor void, which rots joists and floorboards from below. Every one needs clear air in front of it, and if the ground cannot be lowered enough, a periscope vent raises the opening instead.
9. Wait a full heating season before judging it.The wall will look no different for weeks. Take a photograph now and another in twelve months.

Tips

• Where a path cannot be lowered — a shared passage, a legal boundary, a drive — a drainage channel along the wall taking water to a gully is the usual alternative.
• A gravel margin against the wall is also the cheapest way to keep splashing rain off the brickwork, which stops the lower courses staying wet in winter regardless of the barrier.
• If you are having landscaping done, put the clearance in writing at quote stage. Landscapers build up to the level they are given and it is nobody's job to notice the damp course.

Common mistakes

• Laying a new patio or drive over the existing one — Every layer raises the finished level. Two overlays is enough to bury a correctly built damp proof course, and the damp appears inside a year or two later when nobody connects the two events.
• Filling the dug margin with soil or mortar to tidy it up — Soil holds water against the wall, which is the problem you just dug out. The margin has to stay free-draining.
• Digging a deep trench right against the wall — The wall's footing is not far down. A narrow margin is all that is needed; a trench risks undermining the foundation.

Questions people ask