# Damp at home: is it the roof or something else?

> Roof, condensation, rising damp, plumbing, facade or windows: how to tell each cause by its look, its season and its place, with a simple diary and who to call.

- Page: https://telhadoseguro.pt/en/guides/damp-at-home-roof-or-something-else
- Language: English
- Updated: 2026-11-03

## Summary

- When and where the stain appears says a lot: only with rain points to the roof, cold mornings to condensation, always growing to plumbing or the ground.
- Condensation comes from water vapour indoors and weak ventilation, and swapping tiles does not fix it.
- A two-week diary with dated photos and the weather helps the technician and the insurer.
- Each cause has its own professional: roofer, plumber or an independent technician who diagnoses first.

A dark stain on the ceiling, mould on a wall, paint that blisters. Many people decide at once that the roof is bad and pay for a repair that fixes nothing. Damp at home has five or six origins, and only one of them is the roof. This guide helps you tell them apart by what you see, when it shows up and where, and says who to call in each case. For roof leaks themselves, see the [guide to roof leak causes](https://telhadoseguro.pt/en/guides/roof-leak-causes).

*Updated 3 November 2026. General information, not a replacement for a technician's visit. Where we write "common practice", it is general building knowledge with no specific official source.*

## The essentials

- **Timing says a lot.** Only after rain points to the roof, the facade or a window. Cold mornings in winter, even without rain, point to condensation. All year round, or always growing, points to plumbing or the ground.
- **Place says a lot too.** At floor level on lower walls: ground moisture. On the top-floor ceiling: roof or condensation. Near windows and cold corners: condensation.
- **Condensation is the most likely cause of mould** in a housing-association leaflet we read. It comes from water vapour inside the home and from ventilation.
- **Take dated photos, once a week, and note the weather.** This is worth more to a technician than any guess.
- **Do not climb onto the roof.** Almost everything can be seen from the ground.

## The six causes, one by one

**1. Roof or covering.** Water gets in through a broken tile, a ridge, a flashing or a gutter and leaves a stain with an outline, sometimes with a darker ring. It appears **during or soon after rain**, usually on the top floor or near a chimney. It can dry between showers and return with the next. The APICER and CTCV technical guide describes these faults in detail.

**2. Condensation.** Indoor air carries water vapour from showers, cooking, drying laundry and breathing. When it touches a cold surface, the vapour turns into drops. A 2003 paper by researchers at FEUP (University of Porto) links condensation to the balance between the vapour produced and the ventilation, and says it appears when ventilation is weak or unevenly spread. Common practice says it shows up **on cold days, even without rain**; forms on glass, in outer-wall corners, behind wardrobes and along the ceiling; is spread out with black mould in tiny dots; and is worse in the morning.

**3. Rising damp (from the ground).** Water in the soil climbs through the pores of walls and floors by capillary action. That is what a 2008 technical note from the FEUP Building Physics Laboratory describes. A British housing leaflet says it only affects ground-level spaces. Common practice: it shows **at the base of walls**, with crumbling plaster, white salts and peeling paint, and changes little from day to day. It is typical of old houses with no damp barrier at the base.

**4. Plumbing leak.** A pipe, a water heater, a cistern or worn shower seals can wet walls and ceilings. The Belmonte town council leaflet suggests a test: turn off everything that uses water, note the meter and see whether it moves. Common practice: the stain **grows in dry weather**, does not follow the weather, and is usually near a bathroom, kitchen or a wall with pipes.

**5. Facade infiltration.** Heavy rain driven by wind gets in through cracks in the render, open joints or an unprotected wall. Common practice: the stain appears **on the wall, after wind-driven rain**, on the most exposed side, rather than on the ceiling. The British leaflet calls it "penetrating" damp: water coming from outside.

**6. Windows and shutter boxes.** A badly sealed window lets water in, and a shutter box is a cold spot where condensation forms. The mark sits **around the window**. If there are only drops on the glass, it is almost always condensation.

## The two-week diary

Common practice, at no cost:

1. Photograph the stain every day or every second day, from the same spot, with a coin beside it for scale.
2. Write next to it: rain or not, wind, morning temperature, whether there was a shower or laundry drying.
3. Mark the outline of the stain on the wall in pencil, with the date.
4. Once, do the water meter test.
5. Put everything in one folder. The [damage file tool](https://telhadoseguro.pt/en/roof-damage-file) helps organise photos and dates, which is useful if you speak to your insurer.

Grows only with rain: infiltration. Grows on cold mornings: condensation. Always grows: pipe or ground.

## What you can check without climbing

- **Outside, from the ground:** broken or displaced tiles, the ridge, full or overflowing gutters, loose downpipes, cracks in the render.
- **Indoors:** ventilation in bathrooms and the kitchen, blocked vents, furniture pressed against outer walls, laundry drying inside.

On ventilation, the same FEUP group mentions Portuguese recommendations of about one air change per hour in bedrooms and living rooms and four in service spaces, and suspects that many new homes do not reach them. The British leaflet advises opening windows after showers and cooking, and keeping a steady temperature so walls do not get very cold.

## Who to call

| Cause | Who |
|---|---|
| Roof, flashings, gutters | Roofing contractor. See how to [choose a contractor](https://telhadoseguro.pt/en/guides/choosing-a-roofing-contractor) and [check them](https://telhadoseguro.pt/en/roofing-contractor-check) |
| Plumbing | Qualified plumber; shut the main valve if urgent |
| Condensation, ground, facade | Independent technician (civil engineer or architect) who diagnoses before quoting |
| Apartment block | Building administrator, if the roof is a shared part |

Be wary of anyone selling "damp treatment" without naming the cause. Ask for the quote to state it. You can compare with the [quote checker](https://telhadoseguro.pt/en/roof-quote-checker). For roofs, the [repair hub](https://telhadoseguro.pt/en/roof-repair) explains the steps.

## Insurance

According to our [home insurance guide](https://telhadoseguro.pt/en/guides/home-insurance-storm-roof), which cites the law firm CMS, water entry is usually covered only when it comes from sudden damage, and old damp and lack of maintenance are usually excluded. That is why a diary with dates and photos matters: it shows the damage is recent and tied to an event. Read your policy.

## What we could not confirm

- **LNEC and ADENE documents** on this topic. Our searches returned none we could read. We used FEUP papers.
- **DECO Proteste articles** on damp. We could not open the page, so we do not cite them.
- **Ideal humidity and temperature values** for Portuguese homes.
- **Your house.** Only a visit confirms the cause. We read only the abstracts of the FEUP texts.

## Sources (read 3 November 2026)

- M. Pinto and V. P. de Freitas, [Importância da ventilação nas condensações superficiais](https://repositorio-aberto.up.pt/handle/10216/91605), PATORREB 2003, FEUP (abstract).
- M. Pinto, J. Viegas and V. P. de Freitas, [Qualidade do ambiente interior em edifícios de habitação](https://repositorio-aberto.up.pt/handle/10216/98522), 2007, FEUP (abstract).
- V. Freitas, M. I. Torres and A. S. Guimarães, [Humidade Ascensional](https://repositorio-aberto.up.pt/handle/10216/100632), FEUP Building Physics Laboratory, 2008 (abstract).
- P. N. S. Pinto, V. P. de Freitas, [Caracterização de Barreiras Pára-Vapor e sua Aplicação](https://repositorio-aberto.up.pt/handle/10216/96793), FEUP, 2002 (abstract).
- APICER, coordinated by CTCV, [Guia para Projeto e Aplicação de Telhas Cerâmicas](https://www.apicer.pt/apicer/media/5c06bd0e8d436.pdf), 2018.
- Câmara Municipal de Belmonte, [Suspeita de uma fuga de água em casa?](https://www.cm-belmonte.pt/wp-content/uploads/2026/05/Suspeita-de-uma-fuga-de-agua-em-casa-1.pdf), May 2026.
- RBH (British housing association), [Humidade, Condensação e Bolor](https://www.rbh.org.uk/media/3614/humidade-condensação-e-bolor.pdf), translated leaflet, 2023. General guidance, not a Portuguese standard.

## FAQ

### How do I know if the stain is from the roof or condensation?

If it shows up during or right after rain and has an outline, it points to the roof. If it appears on cold mornings without rain, with dotted mould and misted glass, it points to condensation.

### Can a stain that grows in dry weather be the roof?

Unlikely. Growth without rain usually means plumbing or ground moisture. Turn off all water and see whether the meter moves.

### Does insurance pay for damp at home?

According to our guide, water entry is usually covered only when it comes from sudden damage, and old damp is usually excluded. Read your policy and keep dated photos.

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Source: https://telhadoseguro.pt/en/guides/damp-at-home-roof-or-something-else. Independent information, not legal or tax advice.