Getting a retrofit right

Mushrooms growing on walls, attics dripping with condensation – the perils of a retrofit that’s been poorly designed or executed are severe. The good news is, it’s easy to avoid the heartache by being realistic about the budget, finding the right people to do it, using appropriate materials, and planning it in advance. That’s right! There are no shortcuts to a quality job.

Over the coming years it is likely that everyone will be required to carry out a deep energy renovation of their home; upcoming EU directives and international agreements (COP21) are already starting to change national policy. But while it’s a good idea to get ahead of the game, it’s important to understand what the rules are.  

There are some real horror stories emerging from the home energy renovation industry, bizarre ill-fitting insulation, attics dripping with condensation, bad indoor air quality and mould growth on walls. This is mostly due to people and contractors cutting corners, oftentimes because they want to save money but also because they lack knowledge of building physics. 


First things first 
There is no way around this first point, and that’s to get independent advice from a professional. Their key function is to draw up a detailed and independent hygrothermal analysis of the building to determine what should be done and how.   

In the calculations a lot of variables have to be considered: exposure to rain, house orientation, structure, etc. Taking into account planning restrictions, this will lead to the selection of the most appropriate insulation choices (where to put it, what type and thickness) for your house, not just the stuff that happens to be left over in the back of the builder’s white van!  

The resulting strategy to achieve a good energy rating (B3 or better) will also prioritise the order of work. The sequence is vital to get right and if you don’t have the money to do it all at once, it allows you to do it in stages.  

Making it up as you go along is not a recipe for success, there are just too many things to consider.  

Bang for your buck 
When hiring a designer or retrofit contractor ask an independent professional for recommendations. Don’t just rely on word of mouth from neighbours; they may be lovely fellows who do a perfect decoration and painting job and don’t leave a mess, but there is no point in having a beautiful finish if your walls and roof are rotting behind it.  

Credentials In the case of a designer check that they are on a statutory register, part of a professional body and that they have completed courses/training in this area of expertise. Ask for references and visit homes they’ve overseen work on.  

In the case of an installer, check if they are on a recognised contractors’ list. For NI this could be registration on the BBA installers’ list, the Cavity Insulation Guarantee Agency or the UK’s National Insulation Association. Some will also have the UK government endorsed Trustmark which is intended to signal competence and adherence to standards.  

In ROI you should only use the Sustainable Energy Authority of Ireland (SEAI) approved contractors’ list or check they’re an approved installer with the NSAI. Some contractors are directly associated to insulation manufacturers, being trained on a regular basis on their systems. In case something goes wrong the benefit to the homeowner is that adequate recourse can generally be found. This linkage with specific manufacturers is a current requirement of all members of the National Insulation Association of Ireland.  

Reference material Check that the guidance they are using is up-to-date and specific to Irish conditions. In ROI there is a National Code of Practice for retrofit published by the National Standards Authority of Ireland (SR54) which sets out the science and good practice for retrofit. The Building Research Establishment (BRE) and the Sustainable Traditional Building Alliance (STBA) also provide excellent reference material for both designers and contractors.  

Training Ensure everyone working on the job is trained. It’s important that the workmen who are actually doing the work understand what they’re doing and why, not just their bosses.  

Covered Designers, contractors and installers must have up-to-date insurance and be tax compliant. 

If you can’t get this information or a straight answer to all of this, start backing away. The energy renovation industry is new and there is still a huge level of ignorance so you need to make sure you hire someone who understands the pitfalls of retrofit and how to avoid them. 


An important aspect to be aware of is that once you start adding insulation, you change the physical properties of the home. We produce a lot of moisture by breathing, cooking, showering, and drying clothes, all of which needs to be properly managed. 

For example older structures partly relied on draughts from the windows and chimneys to provide fresh air. Once you start replacing older leakier windows with modern triple glazed units and sealing these up to the wall you are creating a need for ventilation to come from somewhere else. 

Another common example is one where you add insulation to your roofspace floor – in that case the area will become much colder because it will be getting less heat from the house. But some moisture will still get up there, and it will condense into water to drop back onto the insulation. 

Without increasing ventilation within the roof this moisture will build up over time and eventually, your roof timbers will rot.  


It is a requirement of an SEAI grant in ROI to increase roof ventilation when undertaking this type of work but unfortunately many contractors are telling homeowner not to bother. They will be long gone before you notice the problem.   

It is vital that you also increase the level of ventilation in the house as a whole once you start insulating and making it more airtight. A properly designed ventilation system will guarantee good indoor air quality – you and your home need fresh air to stay healthy.  

There are many different systems so you don’t need to go top of the range to get the required effect even when a forced/mechanised ventilation system is required. 

The deed is done… 
So what to do if something goes wrong? If you have used an approved installer you can go back to them as they should not want to risk losing their accreditation, and if they can’t fix it they should have the insurance to do so but that’s if they accept wrongdoing.  

Sometimes it may just be a localised issue that can be easily rectified. Condensation in roof spaces can be remedied by unblocking eaves ventilation which is often filled during installation and adding slate or ridge vents to provide cross ventilation. Air leakage from the living space into the roof space may also need to be minimised – this can include making sure any openings made in the ceiling are sealed up (and made safe if electrical).  

There was an instance where homeowners complained of condensation throughout the house which surprised everyone as there was a proper demand controlled humidity activated ventilation system installed. The investigation showed that they had placed a heavy suitcase in the roof space on top of the flexible extract duct from the bathroom so it had ceased to work. The solution in this case was easy: move the suitcase! This is not uncommon with ventilation systems, people forget that they need to be kept running.  

Sometimes an energy upgrade has been carried out and ventilation has not even been considered so it is hardly surprising when condensation occurs. The solution to this is to install a ventilation system. Other issues such as bad workmanship or using the wrong materials may be a bit more difficult to resolve. This is where it is best to go back to an experienced professional who can help work out the best course of action for the particular problem.  

Costs can quickly add up if this is the case. While external insulation could readily set you back €10,000/£8,000 to rectify, it will probably be dearer to have to correct internal wall insulation due to the associated refurbishment and/or structural costs.  

For example, floor joists can become compromised as a result of poor internal wall insulation. In a bathroom the cost of replacing poorly fitted insulation could result in having to get a new one. You may also need to move out while the remedial work is taking place, which you wouldn’t in the case of an external wall refit. And the list goes on. A stitch in time… ν

Pat Barry and Astrid Madsen  

Irish Green Building Council, 


Additional information: 

Liam O’Gorman of the NIAI, Niall Crosson of Ecological Building Systems, 

Paul Kenny CEO of the Tipperary Energy Agency which supports homeowners who wish to complete a deep retrofit of their home with renewable heating and mechanical ventilation. 10 homes were upgraded in 2015 to A2/A3 standard and a further 25-30 for 2016 are likely. See 

Read up and watch videos that explain concepts such as thermal bridging, interstitial condensation, together with case studies and stories on 

Installers ROI:,, 

Installers NI:,, 

Also see and 

Planning Responsible Retrofit of Traditional Buildings from the Sustainable Traditional Buildings Alliance 

Grants: ROI, NI 


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About Astrid Madsen

Astrid Madsen is the editor of SelfBuild & Improve Your Home magazine. She previously held the same role in an Irish trade publication, before that she worked at the National Standards Authority of Ireland. She graduated with a BA in Urban Studies from Columbia University in New York and holds an MBA from the Instituto de Estudios Bursatiles in Madrid. France of origin, she now lives in Portarlington, County Laois, where she's taken on the task of renovating a listed building! Email

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