---
title: "A damp patch appeared"
url: https://bkgreenstone.com/troubleshooting/a-damp-patch-appeared/
description: "Order the checks by where the patch sits relative to anything that could be wetting it."
---

# A damp patch appeared

## All topics

- IN[Insulation & Air Sealing](https://bkgreenstone.com/topics/insulation-and-air-sealing/)
- WD[Windows & Doors](https://bkgreenstone.com/topics/windows-and-doors/)
- HV[Heating & Ventilation](https://bkgreenstone.com/topics/heating-and-ventilation/)
- PW[Plumbing & Water](https://bkgreenstone.com/topics/plumbing-and-water/)
- ME[Masonry & Exterior](https://bkgreenstone.com/topics/masonry-and-exterior/)
- MF[Millwork & Finishes](https://bkgreenstone.com/topics/millwork-and-finishes/)

## Reference sheets

- [Nominal lumber sizes](https://bkgreenstone.com/reference/nominal-lumber-sizes/)
- [Fastener and pilot sizes](https://bkgreenstone.com/reference/fastener-and-pilot-sizes/)
- [Insulation material guide](https://bkgreenstone.com/reference/insulation-material-guide/)

Order the checks by where the patch sits relative to anything that could be wetting it.

1. Is there anything above the patch that carries water?A pipe, a bathroom, a valley or a parapet above the patch makes an internal leak the first thing to rule out, because it is the only source that is indifferent to weather.[Diagnosing damp in a basement wall](https://bkgreenstone.com/articles/diagnosing-damp-in-a-basement-wall/)
2. Does the patch respond to rain within a day or two?That points outside the wall: ground level, a gulley, a downpipe or a path falling toward the building.[Diagnosing damp in a basement wall](https://bkgreenstone.com/articles/diagnosing-damp-in-a-basement-wall/)
3. Does it have a level upper edge and ignore the weather?Moisture moving up through the structure behaves that way. Check the external ground level against the internal floor before anything else.[Diagnosing damp in a basement wall](https://bkgreenstone.com/articles/diagnosing-damp-in-a-basement-wall/)
4. Is the wall wet on the surface only, and worst in cold weather?That is condensation on a cold surface, and it is a ventilation and surface-temperature problem rather than a water-ingress one.[Ventilation for kitchens and baths](https://bkgreenstone.com/articles/ventilation-for-kitchens-and-baths/)
5. Was the wall repointed recently?A dense pointing can close the route by which the wall used to dry, so the wall gets damper without any new water arriving.[Repointing mortar and why hardness matters](https://bkgreenstone.com/articles/repointing-mortar-and-why-hardness-matters/)

[Back to all troubleshooting paths](https://bkgreenstone.com/troubleshooting/)