Would waterproofing the outside wall solve it?

Occasionally, and it is sometimes appropriate on badly exposed solid walls. More often it seals moisture into the wall and stops it drying outward, making things worse. It is a considered specification, not a default.

My damp is only bad in winter. Is that penetrating damp?

It might be, since winter brings the driving rain. But that is also the classic pattern for condensation, which is worst when the building is cold and closed up. Which one it is needs establishing rather than assuming.

Can you fix the gutter as well as diagnosing it?

Repairs to rainwater goods, pointing and render are within scope. If a fix needs a roofer at height or a scaffold, I will tell you straight rather than improvise.

Damp Treatment

Penetrating damp

Water coming in horizontally rather than upward. Usually a small defect, badly hidden — and the hard part is looking in the right place.

Defective flashing, failed pointing, cracked render, blocked cavities, leaking gutters. Often an easy fix once you know where to look — the hard part is looking in the right place.

How to recognise it

The distinguishing feature is that it responds to weather. Rising damp is fairly constant. Condensation is worst in cold weather and correlates with heating and occupancy patterns. Penetrating damp tracks rainfall, often with a lag of a day or so while the water works through the structure.

It also ignores height. Anything damp above the first metre or so, or on an upper floor, is far more likely to be penetrating damp or condensation than anything rising.

The patch shape helps too. Penetrating damp tends to produce a defined area, sometimes with a darker centre, radiating from the point of ingress. It is a localised fault, not a general condition of the wall.

Where it comes from

Rainwater goods are the most common single source and the cheapest to fix: a blocked or cracked gutter discharging down a wall, a leaking downpipe joint, a gully that no longer takes water away. Years of saturation from a broken gutter will soak masonry thoroughly enough to look like a serious structural problem.

Then the building fabric itself: failed or eroded pointing, cracked or blown render, a defective flashing at a roof abutment, a failed lead soaker around a chimney, perished window sealant, a sill without a working drip. In cavity walls, mortar droppings or misplaced insulation can bridge the cavity and carry water across a gap designed to stop exactly that.

Chimneys deserve special mention. A disused flue with a failed or absent cap, poor pointing and no ventilation collects water and salts and produces persistent staining on the breast that is regularly mistaken for rising damp when it appears at ground-floor level.

Fixing it

Find the defect, fix the defect. Repoint the failed section, repair or replace the flashing, clear or renew the rainwater goods, seal the reveal, cap the flue, clear the cavity. This is usually far cheaper than any internal damp treatment, which is why establishing the cause first matters commercially as well as technically.

Internal work is sometimes still needed once the ingress has stopped, because saturated masonry takes time to dry and contaminated plaster may need replacing. But it follows the external repair rather than substituting for it. Tanking the inside of a wall while water still enters from outside moves the problem rather than solving it.

Common questions

Would waterproofing the outside wall solve it?: Occasionally, and it is sometimes appropriate on badly exposed solid walls. More often it seals moisture into the wall and stops it drying outward, making things worse. It is a considered specification, not a default.
My damp is only bad in winter. Is that penetrating damp?: It might be, since winter brings the driving rain. But that is also the classic pattern for condensation, which is worst when the building is cold and closed up. Which one it is needs establishing rather than assuming.
Can you fix the gutter as well as diagnosing it?: Repairs to rainwater goods, pointing and render are within scope. If a fix needs a roofer at height or a scaffold, I will tell you straight rather than improvise.