Condensation vs Penetrating Damp: How to Tell the Difference
Use this checklist to distinguish condensation and mould from defect-driven penetrating damp—before you pay for the wrong fix.
What condensation usually looks like
Condensation is moisture from indoor air depositing on colder surfaces. It commonly produces surface mould and water droplets during colder months.
- Often on cold bridges (corners, lintels, window reveals).
- Worse in bedrooms, bathrooms, kitchens and poorly ventilated rooms.
- Symptoms fluctuate with occupancy, heating patterns and seasonal weather.
What penetrating damp usually looks like
Penetrating damp is moisture entering through the building fabric—commonly from defects or saturation.
- Localised staining linked to an external defect (gutter, downpipe, roof junction, pointing).
- Can worsen after heavy rainfall and present on exposed elevations.
- May appear as patchy dampness rather than uniform surface mould.
Quick checks before you commission work
- Check rainwater goods: leaks, overflowing gutters, blocked hoppers.
- Look for cracked render/pointing and defective roof flashings.
- Assess ventilation provision and whether trickle vents/extract fans are used.
- Note symptom locations: cold corners vs single wall section under a defect.
Diagnosis should be evidence-led. If the recommendation is “inject chemicals” without defect tracing or moisture pathway explanation, be cautious.
FAQs
Can you have both condensation and penetrating damp?
Yes. It is common to have an external moisture pathway plus internal humidity/ventilation issues. A proper survey separates causes so repairs are targeted.
Does mould always mean condensation?
Often, but not always. Mould can also occur where persistent moisture cools surfaces or where leaks increase humidity locally.
Should I buy a dehumidifier?
A dehumidifier can reduce symptoms short-term, but it is not a substitute for fixing defects or improving ventilation and thermal performance.
Next step
If you are in Chester or nearby, you can also use our location page: Damp Survey Chester.