Under the tiles of an old house there is almost always timber: trusses (asnas), purlins (madres), rafters (varas) and battens (ripas). That timber has three enemies: water, which brings rot, wood-boring beetles (carunchos) and termites. This guide explains how to recognise them from the loft, what is serious, who can assess and treat it, and what to ask for in writing. We do not name firms or give prices.
Updated on 4 November 2026. General technical information. Not a substitute for an assessment by an engineer or a qualified technician.
The essentials
- Water first. Rot fungi and subterranean termites need damp timber. LNEC (2024) gives a moisture content above 18 to 20% for termites. Treating the timber without stopping the leak or the condensation does not solve it.
- Signs of attack do not mean an active attack. At the Ajuda National Palace, LNEC found mostly old termite signs, in timber that was already dry.
- Subterranean termites may leave no signs on the outside. The piece looks whole and is hollow. Only an inspection with tools shows it.
- The weak points are the battens and the bearings on the walls. Trusses and purlins usually hold up better.
- Treatment products are biocides. They must be authorised and used as the label says.
The structure in a few words
The APICER and CTCV technical guide (2018) notes that the vast majority of traditional clay-tile roofs have a timber structure. The main structure is the trusses (asnas or tesouras) and the purlins (madres), which carry the weight to the walls. On top are the rafters (varas), running down the slope, and the battens (ripas), on which the tiles sit. The terms are in the roof glossary.
According to the same guide, the main members are the least vulnerable, because they are better protected and thicker. They fail mainly through fire or through rot from serious, long-running leaks.
The agents and their signs
| Agent | Signs you can see | Source |
|---|---|---|
| Rot fungi | Dark, soft timber that crumbles (common practice), especially near eaves, gutters and bearings | APICER/CTCV; 2015 guidelines |
| Furniture beetle (Anobium punctatum, caruncho pequeno) | Small round holes and granular dust | Canadian Conservation Institute |
| House longhorn beetle (Hylotrupes bajulus, caruncho grande) | Large oval holes and cavities | Canadian Conservation Institute |
| Subterranean termite | Often no sign on the outside; piece hollow inside | LNEC, 2024 |
| Drywood termite (Azores) | Winged insects flying, from May to September | University of the Azores, 2015 |
Termites in Portugal
Mainland. According to LNEC (2024), the subterranean termite Reticulitermes grassei is widely distributed in Portugal. It lives in the soil and moves into buildings when the timber becomes abnormally damp. It eats the inside of the pieces and leaves the outside unchanged. All untreated Portuguese timbers are susceptible, especially maritime pine (pinho bravo). In an LNEC laboratory test (2011), the termites attacked every timber tested, but avoided chestnut when they could choose.
Azores. A University of the Azores report (2015) lists four species in the archipelago. It highlights the drywood termite Cryptotermes brevis, recorded in 2000 and confirmed in 2015 on six of the nine islands, with most impact in the old centres of Angra do Heroísmo and Ponta Delgada. The report notes that the species has already appeared in Lisbon, but thinks it unlikely to spread on the mainland as it has in the Azores.
The region has its own law, Regional Legislative Decree no. 22/2010/A. Government Council Resolution no. 195/2024 sets the parishes (freguesias) considered potentially infested and says that in 2022 and 2023 the drywood termite spread, with new outbreaks in Angra do Heroísmo, Ponta Delgada and Ribeira Grande.
Inspecting from the loft, safely
Do not climb onto the roof: see work at height. The steps below are our own practice, based on what the sources ask of an inspector:
- Step only on joists or firm boarding. The 2015 guidelines say that if the structure is not safe to walk on, it is propped first.
- Hold a torch to the side. Raking light shows holes better.
- Start with the critical points: bearings on the walls, eaves, corners and truss joints, which the guidelines say to check first. Add the areas below chimneys and hips.
- Look for water: stains, run marks, dark timber. See the causes of roof leaks and condensation in the roof void.
- Take dated photos. Do not scrape or drill main members: that is a technician’s job.
Serious or old?
Signs that call for a technician soon (our summary of the sources):
- A sagging roof. APICER and CTCV list marked deformation among the three warning signs, with a risk of structural failure and of pushing the façades outwards.
- Soft timber at the bearings. According to the 2015 guidelines, if rot has gone through the whole cross-section, the member does not count for load-bearing.
- Damp timber next to holes or dust.
- Gutters or eaves damaged for years, which the same guide links to decay of the timber next to the façade.
Often old: holes in dry, firm timber, and rafters that have been bowed for decades. APICER and CTCV say this bowing is often stabilised and has no structural consequence. Only an inspection confirms it. And deformation does not always come from insects: at Ajuda, LNEC put a 60 mm drop in a floor down to beams slipping on their bearings.
Repair, treat or replace
The APICER and CTCV guide describes three cases:
- Bowed but sound rafters: replace the battens, levelled with packers, and treat the new battens against insects.
- Local decay of the main structure, often rot at the bearings: local solutions, without taking everything apart. Splices (próteses), metal or timber reinforcement, or resins, always with calculated props.
- Main structure lost: a new structure, calculated and compatible with the walls. Large changes in weight or bearings need a design.
The 2015 guidelines point out that you must stop the water getting in and let things dry before decay stops. If the work touches the structure, see the works permit. To choose between repairing and replacing it all, see repair or replace the roof.
Who is qualified
- For the structure: an engineer (civil engineer or engenheiro técnico) with timber experience (our recommendation). The sources call for calculations for reinforcement, props and new structures.
- For the treatment: Regulation (EU) No 528/2012 calls products that control organisms that destroy timber, including insects, «wood preservatives» (product type 8). Insecticides are type 18. Article 17 says they must be used according to the authorisation and the label, keeping chemical use to the minimum. Portaria no. 76/2022 names DGS or DGAV as the competent authorities, as the case may be.
- In the Azores: article 14 of the regional decree says who can be a qualified expert in the termite infestation certification system: architects and engineers recognised by their professional bodies or by ANET, experts qualified in another EU state, or graduates with at least 60 credits in Biology, Forestry, Wood Technology or Environmental Sciences, with specific qualifications.
What to ask for in writing
- Which agent was found and whether the attack is active or inactive.
- Timber moisture readings, with their location.
- Where the water comes from and how it will be dealt with before treatment.
- Which members are affected, how much of the cross-section is left and whether there is a structural risk.
- What was not inspected and why, as the 2015 guidelines ask.
- The method (splice, reinforcement, replacement) and the propping.
- The product: trade name, authorisation number, type and safety data sheet.
- The warranty: see roof works warranty and choosing a roofing contractor.
What we could not confirm
- The full text of Decree-Law no. 140/2017 and Regional Legislative Decree no. 22/2010/A. The Diário da República website returned an error on 4 November 2026. Article 14 was read as quoted in a University of the Azores document.
- Whether on the mainland a certification is required for anyone applying biocides against wood insects in a home.
- Which authority authorises wood preservative products (DGS or DGAV).
- Which termites exist in Madeira, and the situation in the Algarve: we found only commercial sources.
- Hole sizes in millimetres, the earth tubes of subterranean termites and the pellets of the drywood termite: commercial sources or papers we could not open.
- The link between the Portuguese common names and the beetle species, which we saw in university papers that were cited but not read.
- An official moisture limit for rot fungi, and whether the Azores termite certificate is required on a sale.
Sources (read on 4 November 2026)
- APICER and CTCV, Guia para Projeto e Aplicação de Telhas Cerâmicas, 2018, chapter 7 (biological agents, inspection, warning signs, cases 8, 9 and 10).
- LNEC, H. Cruz, S. Duarte, L. Nunes and others, Caracterização e diagnóstico de estruturas de madeira do Palácio Nacional da Ajuda, Congresso Construção 2024.
- H. Cruz (LNEC) and others, Guidelines for the on-site assessment of historic timber structures, 2015, University of Minho repository.
- S. Duarte, M. Gaju and L. Nunes (LNEC), Preferências alimentares de Reticulitermes grassei, CIMAD 11, 2011 (abstract).
- O. Guerreiro and P. A. V. Borges, University of the Azores, Monitorização da térmita de madeira seca Cryptotermes brevis nos Açores (2010-2015), February 2015.
- Government of the Azores, Resolução do Conselho do Governo n.º 195/2024, 30 December 2024.
- University of the Azores and LNEC, qualified expert training programme for the SCIT, September 2026 (quotes article 14 of Regional Legislative Decree no. 22/2010/A).
- Regulation (EU) No 528/2012 on biocidal products (article 17(5) and annex V, types 8 and 18).
- Portaria no. 76/2022 of 3 February, read in a copy of the text published in the Diário da República (DGS and DGAV).
- Government of Canada, Canadian Conservation Institute, Major insect pests and their associated, diagnostic signs, 2017 (beetle signs).