A green roof, or living roof, is a roof covered in plants. For a house, the questions are: can it carry the weight, is the waterproofing sound, and who looks after the plants? This guide explains what it is, how it is built, what it costs according to the sector’s association and when it is not worth it.
Updated on 3 November 2026. General information, not an engineering design.
The essentials
- There are three types: extensive, semi-intensive and intensive. The difference is the depth of the growing medium and the plants.
- Weight: according to the Associação Nacional de Coberturas Verdes (ANCV), extensive systems generally weigh less than 120 kg/m² and intensive ones more. Only an engineer can say whether your roof can carry it.
- Waterproofing sits underneath and belongs to the building. On an existing house, the ANCV asks for a membrane in excellent condition.
- It takes work: the ANCV says most green roofs in Portugal need watering, even extensive ones.
- Prices and Lisbon or Porto rules: the only price we found is indicative and comes from the association itself. We did not confirm any municipal rules of their own.
What it is and what types exist
The ANCV describes itself as a non-profit association that promotes green roofs. In its frequently asked questions it describes three types:
| Type | Growing medium | Plants | Maintenance |
|---|---|---|---|
| Extensive | up to 15 cm | succulents and perennial herbs, generally under 50 cm | low |
| Semi-intensive | 10 to 25 cm | herbs, sub-shrubs and shrubs | moderate |
| Intensive | more than 15 cm | may include trees and shrubs | high, like a garden |
The layers, from the bottom up
The Fundo Ambiental, in the guidance for its 2021 programme, separates two things. The waterproofing and the thermal insulation are not part of the green roof: they belong to the building. On top of them go:
- the protection of the waterproofing or of the insulation;
- the drainage system and the filter that separates the drainage from the growing medium;
- the technical substrate, which is not garden soil;
- the plants.
If there is irrigation, the system is part of the design. The same document says to follow the ANCV’s “Guia Técnico para Coberturas Verdes” and to have a specific design, whatever the type.
Weight and structure
The ANCV says the building must be able to carry the extra load and that the building’s capacity is compared with the product data sheet. It gives as a reference less than 120 kg/m² for extensive roofs and more for intensive ones. The synopsis of an exhibition on the subject (Porto Photography Biennial, 2023) describes these roofs on flat or slightly sloping roofs.
We did not find an official table of permissible loads for old houses. On a timber-and-tile roof, do not assume it can carry it. Ask a civil engineer for the calculation, with the substrate wet.
Waterproofing underneath
According to the ANCV, the membrane must resist roots and may need extra protection. On works to an existing building, it should be in excellent condition and, preferably, far from the end of its life. Once the plants are in, finding a leak is expensive. If your roof already leaks, first read the causes of roof leaks.
Maintenance
The ANCV recommends at least one check a year: drainage, invasive plants, fertiliser and organic matter, and irrigation. For extensive roofs it indicates about four visits a year after installation. The Fundo Ambiental’s 2021 programme did not fund maintenance contracts. Looking after plants on a roof is work at height.
The benefits, without exaggeration
The exhibition synopsis cited above and the ANCV point to: rainwater retention, less heat in summer, protection of the waterproofing, better sound, biodiversity. The synopsis gives numbers: the water running off to the drains falls by “about 50 to 90%”, reflected noise drops by up to 3 dB and sound insulation rises by up to 8 dB. It also says the roof can extend the life of the roofing 2 to 3 times.
These are claims by an exhibition and an association, with no study cited. We read no independent study giving the energy saving for a house like yours.
What it costs
The ANCV gives “indicative averages in Portugal”: 40 to 70 € per m² for extensive roofs and 80 to 150 € per m² for intensive ones, varying with the scale and the access to the roof. We saw no date on the page. We did not check these figures against an official source and we did not read prices on private portals. Since the Fundo Ambiental says waterproofing and insulation are outside the green roof, ask whether the price includes them. For VAT, see the roof works VAT guide; we have no ruling from the Tax Authority on green roofs.
Permit, condominium and council
In the RJUE (Decreto-Lei n.º 108/2026, article 2), “alteration works” are those that change the physical or aesthetic characteristics of a building, including the nature and colour of the exterior cladding materials. Article 6-A exempts only replacing the roof material with one that has an exterior finish identical to the original. In our reading, a green roof is not identical. Ask the council in writing before you hire anyone (see the roof works permit guide). In apartment buildings the roof is a common part (Código Civil, article 1421): see condominium roof, who pays.
Aid
The ANCV says the Government launched the Fundo Ambiental in 2020, which co-finances green roofs: 70% of the cost, up to 3,000 €, for owners of occupied homes built up to 2006. The official document we read (June 2021) confirms that type 6 of the programme included green roofs. We found no open call. Check the Fundo Ambiental portal before counting on this.
When it is not a good idea
- Nobody has checked the structure’s capacity.
- The waterproofing is old or the roof already leaks.
- Nobody will water and tend the plants, or access to the roof is dangerous.
- The roof is fibre-cement: read the asbestos guide first.
- The roof is very steep. We found no Portuguese source with the maximum slope.
- The condominium or the council does not approve.
- You only want to save on electricity: we cannot confirm that saving.
What we could not confirm
- Lisbon and Porto rules: we found no municipal obligation or incentive for green roofs in an official source.
- The text of the ANCV Technical Guide: it is paid (we saw the index and the price on the page) and we did not read it. Weights and costs come from the frequently asked questions.
- The status of the Fundo Ambiental aid in 2026.
- The maximum slope and permissible loads on tile roofs of old houses.
- Energy saving and service life backed by an independent study.
- Prices on private portals (Habitissimo, Zaask): we did not read them.
Sources (read on 3 November 2026)
- ANCV, Frequently asked questions, About us and Technical Guide (undated pages; types, weight, cost, maintenance, membrane, aid).
- Fundo Ambiental, 2nd phase of the Programa de Apoio a Edifícios Mais Sustentáveis, Guidance, type 6, June 2021 version (layers, definition, design).
- Synopsis of the exhibition “Green Roofs Grey Roofs”, Porto Photography Biennial, file on fims.up.pt, dated 15 May 2023 (benefits, quoted numbers).
- Decreto-Lei n.º 108/2026, of 29 May, Diário da República, 1st series, n.º 104, articles 2 and 6-A (copy of the official text).
- Mapfre, Regime da Propriedade Horizontal, article 1421 (2003 text; confirm the version in force).