Property Clinic: what can I do about dampness in the attic?

Your property queries answered

Q I've noticed that the rafters in my attic are extremely wet. I've checked that there is adequate ventilation coming into the attic. What else could be causing this problem and how do I fix it?

ARoof timbers within an attic can become damp from two sources. The typical/expected cause is water penetration from the exterior due to a defective roof covering. However, this tends to be readily apparent as you would normally see the defects in the roof covering, and the volume of water penetration would give rise to noticeable damp staining on the ceiling.

The second but less obvious source of dampness on roof timbers is due to condensation occurring from within the attic. Condensation will arise as a result of warm, moist air penetrating up through the ceiling; in the event of the attic not being properly ventilated, this would condense on the underside of the roof covering and give rise to damp staining to all surfaces including the timbers.

Interestingly, the better insulated the attic space is at ceiling level, then the colder the attic will be and thus the risk of condensation occurring will be higher. The problem can be reduced/controlled in two ways. In the first instance, you need to try and reduce the amount of moisture vapour penetrating into the attic in the first place. Moist air is created from everyday activities including cooking, showering, drying clothes etc, and moist air will dissipate throughout the house and up through the ceilings.


Trapdoors within kitchens and bathrooms are very weak points for moist air to penetrate into an attic and thus it is preferable if trapdoors are relocated to corridors or bedrooms. You should also check for any holes/gaps in the vicinity of light fittings etc as this will also allow moist air to penetrate the ceiling. You will also need to ensure that any extractor fans serving kitchens and bathrooms are properly ducted out through the roof and are not simply depositing moist air into the attic.

The second issue to concentrate on is ensuring the attic is properly ventilated in order to minimise the risk of condensation occurring here. It is important to have a strong through-flow of air to an attic space. You should find your attic to be cold and breezy above the insulation. In this respect, you should check to ensure that the vents are clear/unblocked and/or provide additional vents to ensure adequate levels of ventilation.

Provided that you cut down on the sources of moisture entering the attic and ensure that the attic is properly ventilated, then this problem will disappear. More often than not the staining to the timbers will not have any lasting damage, apart from discolouration to the timbers.

However, if the condensation has been going on for a long time, you may find yourself having to carry out some localised timber treatment work. Your local chartered building surveyor will be able to advise further on this if necessary.

Val O’Brien sits on the Building Surveying Professional Group of the Society of Chartered Surveyors Ireland

Q I am thinking of doing Airbnb in my home, as several of my friends are now doing this. I may either offer one room in my house, or the entire house. What I would like to know is: what, if any, are the tax implications for anyone doing Airbnb in Ireland? Do they have to declare this income? Will it be charged retrospectively to those who have been doing Airbnb for a period of time already? Are there any insurance implications in doing Airbnb should someone injure themselves in my home while staying?

AFounded in 2008, Airbnb already has over 600,000 listings of people renting out accommodation across 190 countries, so this is a query which will become more and more topical over time, both for users of the site and for similar sites which will no doubt appear.

Firstly, I always recommend to anyone planning on taking in additional income to check with their accountant regarding the tax implications. The Revenue Commissioners’ website,, provides lots of information around rental income and this should be your first stop in educating yourself further on what tax you would be liable to pay. While there are allowable deductions and reliefs available, as a general rule you need to disclose any additional income; in most cases, that income will be subject to tax.

I would also consult the Airbnb website itself as its Help Centre provides guidance entitled, “How do taxes work for hosts?” which covers both local tax and Value Added Tax. It states that Airbnb is “required to collect VAT on its service fees in countries that tax Electronically Supplied Services” (this includes Ireland) and as part of the EU, “you may need to assess VAT on the services you provide” and to consult a tax advisor.

Many people have income streams that they do not declare either through ignorance of the regulations or simply through taking a chance. Unfortunately for non-declarers, neither of these excuses will be deemed acceptable should the taxman come looking for his share. It is always better to pay tax due as it falls, as the penalties and arrears can be onerous.

With regard to your household insurance, insurers generally cover third-party liability, and guests would be included in this. However, you should contact your insurer directly to check if this includes paying guests.

Like everything else in life, there are pitfalls and it’s better to figure it out before you start. Your accountant or tax consultant would be best placed to advise you on the tax liabilities specific to your situation.

Simon Stokes is Chair of the Residential Agency Professional Group of the Society of Chartered Surveyors Ireland

Q I am extending onto my home and renovating the existing structure. My house is currently insulated to a high standard and I want my extension to be well-insulated also. What tips do you have to reduce unwanted air infiltration into the fabric of my home?

ACurrent building regulations make recommendations to achieve airtightness in dwellings. This is expressed as "air leakage", when the building is subjected to a differential air pressure test of 50 Pascal – a metric unit for pressure measurement. New homes are subjected to an initial test, so any weaknesses found can be easier to address before completion. Improved control of air infiltration into a building is achieved by paying particular care and attention to the workmanship necessary to fully close and seal all interfaces between the various component parts of the building. Seal around all floor, wall, window and roof junctions and all service penetrations for wiring, plumbing and ventilation ducting. It's important to have continuity of insulation between the walls and roofs. Ceiling insulation in the attic void at eaves level should overlap cavity wall insulation, whilst maintaining air flow into the attic. Any imperfections in the external facades such as cracks in plasterwork, open vents etc should be sealed.

The addition of pumped cavity wall insulation can help, and external insulation will keep the structure warm while sealing the outer walls. Alternatively, internal insulated dry lining can be beneficial as well. If the new roof is to be flat or very low pitch, then consider a proprietary warm roof system, which negates the need to ventilate the void beneath. This will also keep the roof structure warm.

Also look at the quality of prefabricated components such as windows and doors. Check manufacturers’ test data for airtightness performance. Typically for a domestic window in the west of Ireland, for example, I would look for data to show successful testing at a minimum of 600 Pascal. Some windows supplied are tested to 300 Pascal pressure, but the degree of exposure is important in choosing the correct product.

It is common today to use tapes internally over all junctions between building elements. Look up manufacturers who provide tapes and seals for airtight solutions. You can also download details from

Finally, use a builder experienced with current techniques for airtight construction. Jim Drew is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland Send your queries to or to Property Clinic, The Irish Times, 24-28 Tara Street, Dublin 2. This column is a readers' service. Advice given is general and individual advice should always be sought