A blocked gutter or a cracked downpipe pours rainwater over the facade instead of carrying it to the storm drain. The wall stays wet for hours, sometimes days, and the damp eventually shows on the inside. This guide explains how to recognise the problem, how to inspect without putting yourself at risk, what can be repaired, and who is responsible in a house and in a block.
Updated on 4 November 2026. General information, not a substitute for a technician’s assessment or legal advice.
The essentials
- The two commonest faults are a blocked gutter that overflows and a leaking downpipe. Cadw (Wales) says the most common cause is a blockage, often cleared by hand.
- Signs outside: stains and green growth on the wall below the gutter or along the pipe, rust, moss or algae (Cadw; Building Conservation).
- Signs inside: stains that appear after rain, on the top-floor ceiling or on outside walls. That separates this from damp rising from the ground.
- Inspect while it rains, and safely. If the gutter is high, call a professional.
- In a block, the roof and the general installations are common parts (Código Civil, artigo 1421.º, the Portuguese Civil Code). The matter goes to the administrator, not to a neighbour.
How a gutter wets the wall
The gutter collects roof water and leads it to the downpipes. If it is full of leaves, soil or nests, water backs up, spills over the edge and runs down the facade. Building Conservation (UK) describes this case: autumn leaves clogging the fittings cause concentrated, prolonged wetting of walls and cills.
The same happens when a gutter sags or loses its fall: Cadw says to look for sagging or misaligned gutters, because water then stands instead of running to the pipe.
Inside, the result looks like other kinds of damp. To tell them apart, see the types of damp in walls. Building Conservation warns that a high reading at the foot of a wall may come from a leak higher up, running down inside the wall.
How to recognise it
| Where to look | What to look for | Source |
|---|---|---|
| Facade below the gutter | Dark or green band, wall wet after rain | Building Conservation |
| Along the downpipe | Rust, water stains, moss or algae on the wall beside it | Cadw |
| Eaves and gutter | Plants growing, sagging gutter, disconnected pipe, missing grille | Cadw |
| Inside, top floor | A ceiling or upper-wall stain that appears or grows after rain | Building Conservation |
A practical rule of ours: compare the dates of the stains with rainy days. If the stain grows when it rains, the water comes from outside. If it also grows in dry weather, see how to find a water leak in a wall.
Inspect and clean safely
Cadw says the best time to check gutters and drains is during heavy rain, because you can see where water overflows or drips. You can do it from the ground, without climbing. Also check whether the downpipe ends in a drain or right at the wall.
If you must climb, safety comes first. For very high or awkward gutters Cadw suggests hiring a scaffold tower or a mobile lift, or using a professional. The HSE (UK) asks users to check a ladder before every use. Summaries of its leaflet also give the 1 in 4 angle (base 1 metre from the wall for every 4 metres of height), three points of contact, and not leaning out sideways. We did not read the original leaflet, and it is not a Portuguese rule.
Wear stout gloves to remove debris (Cadw). Do not go on a roof in rain, wind or moss. In a block, do not enter the common roof without the administrator knowing.
What to repair
- Clean. Remove leaves, soil and plants from gutters, gullies and outlets, especially in autumn and winter (Cadw). Clear the downpipe and the drain it ends in.
- Add protection. Cadw recommends grilles at the outlets against blockages, and notes that trapped water that freezes can split pipes.
- Correct the alignment. Refix a sagging gutter. If it overflows with no blockage, Cadw allows that the system may be too small for heavy rain and that an extra downpipe may help.
- Replace broken parts: cracked sections, open joints, loose brackets.
- Take water away. Building Conservation says to improve drainage at ground level. See damp in basements and buried walls.
Only once the outside water is under control is it worth treating the inside. Measure the drying (moisture meter), see salt on walls if there are white deposits, and repaint as in painting after a leak is fixed.
Flashings
Flashings (rufos) are the strips that join a roof to walls, chimneys and parapets. If they are loose or open, water gets in even with a clean gutter. The sources we read do not cover them, so we give no rules. A stain beside a chimney or a parapet wall needs a professional who can go on the roof.
Whose duty it is
House. The roof and gutters belong to the house owner, and upkeep is theirs. The legal duty to maintain buildings is in the Regime Jurídico da Urbanização e Edificação (the urban development and building regime), but we could not open the official text (see “What we could not confirm”).
Block under horizontal property. Artigo 1421.º, n.º 1, of the Código Civil makes common the structure, the roof and covering terraces (b) and the general installations for water, electricity, gas and the like (d). In a Relação de Guimarães judgment (3 March 2022), the first-instance court treated the rainwater collection and facade downpipes as common parts under those two sub-paragraphs and ordered the condominium to pay. We read only an excerpt, without the appeal result: it is one case, not a rule.
In practice: if the water comes from the gutter or pipe on the common facade, write to the administrator with photographs, as in the condominium guide. That guide explains the majorities, urgent works and what to do if the administrator does not act. For painting the facade see condominium and council. For damage inside your flat see home insurance.
Step by step
- In heavy rain, look from outside to see where water overflows or drips.
- Photograph the stains, dated, inside and out.
- Clean what you can reach safely; call a professional for anything high.
- Repair faulty parts. In a block, tell the administrator in writing first.
- Let the wall dry, measure, and only then redo the finish.
What we could not confirm
- The official text of artigo 89.º of the RJUE (duty to maintain buildings): the Diário da República page would not open. We saw only references in blogs and a court judgment.
- Any Portuguese rule setting how often gutters must be cleaned, or how they are sized.
- The appeal result of the Guimarães judgment, and the original HSE leaflet on ladders.
- Cost of cleaning or repair: no dated public source, so we give no figures.
Sources (read on 4 November 2026)
- Cadw (Welsh Government), “Rainwater disposal”, https://cadw.gov.wales/rainwater-disposal. Read: inspection, cleaning, sagging gutters, grilles, downpipes, work at height.
- Building Conservation, “Rain Penetration”, https://buildingconservation.com/articles/rain/rain.htm. Read: signs, green staining, leaves in gutters, remedies.
- HSE (UK), “Ladders”, https://www.hse.gov.uk/construction/safetytopics/ladders.htm. Read: check before each use. Angle and points of contact: cited through summaries of leaflet INDG402, not read directly.
- Código Civil, artigo 1421.º, text at https://informador.pt/?p=157454 (unofficial copy). Read: n.º 1 (a) to (d), n.º 2 and 3.
- Tribunal da Relação de Guimarães, judgment 2184/19.5T8BRG.G1, 3 March 2022, https://vlex.pt/vid/acordao-n-2184-19-1032051485. Read: excerpt of the first-instance decision.