Why in autumn?
Waterproofing faults usually stay quiet through the summer and surface with the first heavy rainfall. At that stage intervention is both difficult and expensive, because the ground is saturated and excavation is not possible. A check carried out in autumn catches the problem while it is still cheap.
1. Roof drains
Leaves, birds' nests and grit block drains. A blocked drain causes ponding on the roof, ponding shortens the life of the membrane, and winter freeze thaw cycles accelerate the damage. Also check that the protective basket over the drain is still in place.
2. Downpipes
If the bottom of the pipe does not discharge far enough from the building, all the water from the roof is emptying around the foundation. That creates an unnecessary load even in buildings that have foundation drainage. The downpipe should be extended at least a metre and a half away or connected to the stormwater line.
3. Ground fall around the building
For the first two metres out from the wall, the ground should slope away from the building. Fill that has settled over time creates a reverse fall and water collects at the base of the wall. It may not be obvious by eye; watching where the water goes during rain is the most practical method.
4. Drainage chambers
Lift the cover and look inside. If silt has built up at the pipe mouths it should be cleaned out. Standing water permanently sitting in the chamber may indicate a blockage in the discharge line. This once a year check extends the life of the system considerably.
5. Basement walls
Look for white salt crust, blistering paint or mould staining at the base of walls. These are early signs that water is entering the structure. If they have appeared recently, photograph and date them so you can compare at the next check to see whether they have spread.
6. Terrace and balcony joints
Check the mastic joints at parapet junctions and at floor to wall corners for cracking or separation. These joints are the weakest link in the waterproofing and harden and crack over the years under UV exposure. Renewing them is cheap; neglecting them is expensive.
When to call a specialist
If there is a damp patch spreading on a wall, rust coloured staining running down concrete, or unexplained wetness on the floor, the self check stage is over. These signs indicate water entering the structure, and locating the source requires measurement.
Why these checks belong in autumn
Most waterproofing problems surface in winter, because rainfall increases, the freeze thaw cycle begins and the building meets its harshest conditions. But winter is the hardest time to intervene: liquid systems do not cure below dew point, bituminous membrane becomes brittle in the cold and excavation is difficult in wet weather.
Autumn is therefore the right time. Problems are visible while still small and the weather is still suitable for the work.
What to check on roofs and terraces
Outlets. Leaves, dust and nesting material accumulated over summer are cleared. Not only the grating but the basket beneath it must be checked. A blocked outlet turns a terrace into a pool in the first heavy rain.
Signs of standing water. If water remains on the terrace after rain there is a problem with the falls. Even in dry weather the dirt rings left by previous ponding can be seen.
Joints in the finish. Joints that are darkened, mossy or losing grout are letting water through. Tap the tiles lightly, a hollow sound indicates a void beneath.
Parapet base and coping. The upper termination where the waterproofing runs up the wall is checked. Make sure the coping falls towards the terrace and carries a drip edge.
Penetrations and fixings. The mastic and tapes around chimneys, vents, aerials and balustrade fixings age. Anything cracked or lifting is renewed.
What to check on elevations and around the building
Rainwater downpipes. Check for blockages. More importantly, look at where the pipe discharges. A downpipe discharging at the base of the building is directing all the roof water at the foundation.
Falls around the building. The ground should fall away from the building. Settlement or landscaping work over time may have reversed that fall.
Drainage chambers. Where inspection chambers exist, open the cover and observe accumulated silt and the water level. A chamber that stays permanently full indicates a blocked line.
Damp marks at ground level. A horizontal band of damp along the lower part of the wall may mean the waterproofing was not carried high enough.
What to check in the basement
Record newly appearing stains on the wall face, salt efflorescence, blistering paint and crumbling plaster. Whether there has been any change since last winter matters, because an advancing problem and a static mark are different things.
A simple observation is enough to tell whether basement damp is a leak or condensation: if it concentrates on cold surfaces and in poorly ventilated corners, and continues during dry spells, it is probably condensation. In that case ventilation rather than waterproofing is the solution.
Situations that count as risky going into winter
If any of these three applies, act before winter arrives. Where terrace tiles have debonded and water is getting underneath, the freeze thaw cycle will strip the finish rapidly. Where a drainage chamber stays permanently full, the line is blocked and the basement will take water in the first heavy rain. Where a damp mark in the basement has grown noticeably since last winter, the process is advancing and waiting will enlarge the scope of the repair.