Finished retrofitted interior with wall vents. Photo:  Matteo Tuniz Photography

Finished retrofitted interior with wall vents. Photo: Matteo Tuniz Photography

Alan Burns

Question: I live in a two-storey detached 1970 property (210sqm) which is heated with oil radiators and a back boiler stove. I have condensation in some of the external walls but a particular room that was converted from a garage is very bad. The walls were pumped about 13 years ago and the attic is insulated and there is double glazing throughout. Would a heat ventilation recovery system solve this problem and how much would it cost? And how do you make an older house airtight?

Answer: Unfortunately condensation is a very common problem in our damp Irish climate. All too often it will develop into a mould problem if not tackled. The source of the condensation is usually poor ventilation, poor insulation or insulation in the wrong places. It could also be made worse by high humidity levels in the house such as drying clothes indoors.

You don’t mention whether your problems started or got worse after your insulation works but it’s safe to assume that they did. Many people embark on insulation upgrades without fully understanding the potential pitfalls.

Firstly, when insulating a house, you need to do so as completely and evenly as possible. Heat moves from hot to cold areas. When a house is unevenly insulated, the weaker areas will actually have more intense heat loss than they did before. This often lowers the surface temperatures in these areas below the critical dew-point temperature, and condensation is the result.

If you pump your wall cavities, the consistency of insulation fill is unknown because of unseen obstructions in the cavity itself, and it will have weak points or ‘cold bridges’ around windows and doors.

External insulation is always a better solution as it has fewer cold bridges if done correctly, but it is always much more expensive. The good news is that you would have had to pump your cavities before externally insulating anyway so that option remains open to you in the future.

Your former garage may be more problematic for a number of reasons. Firstly, I expect that it has more external walls or roof area to lose heat from than other rooms – and this will be even worse if it faces north or east.

Finally, it is also likely to have a concrete flat roof – there is a common misconception that 1970s flat roofs leak. Of course, some do but most often the problem is condensation rather than rain. If your concrete roof is cold or insulated from below, then any humidity from inside the room will find a dew point and condense within the concrete only to drip back down into the room.

Concrete roofs are best insulated from above with a good vapour barrier on the warm (or room) side of the insulation – this requires a re-roofing. If it is a timber roof construction, then it’s possible that it is inadequate ventilated.

Adequate room ventilation, typically a 100mm (4 inch) wall vent, will often prevent condensation but may not always fully eliminate the problem. As your house dates from the 1970s, there is a good chance that not all the rooms have wall vents. It would be a good idea to check that you have them, and that they are not blocked with old socks or scrunched up newspapers!

Heat Recovery Ventilation (HRV) would probably solve your condensation problems, however, it would be costly to retrofit and expensive to run. A HRV works on the basis of extracting warm, stale air from humid areas such as kitchens and bathrooms, and replacing it with balanced fresh air delivered to bedrooms and living areas.

The heat from the stale air is used to warm the incoming air which reduces the amount of heating needed overall. However, the system is best suited to new build houses or deep retrofit projects where the level of air-tightness and insulation is extremely high. Otherwise, the system is sucking in external air through the gaps in the walls, floors or windows and then filtering and heating it at a significant strain to the fan and at a high energy cost.

A better solution for a retrofit with lower levels of insulation and airtightness is a Demand Controlled Ventilation (DCV) or Positive Input Ventilation (PIV) system. Both are much cheaper and easier to retrofit. They also ensure a good number of air changes that should keep condensation and mould issues under control.

Typically they run continuously in your attic space using a 13W motor which is relatively cost effective to run (less than €30 a year). I would estimate that on your house a DCH system would cost about €2,500 – €3,500 to install, including electrical work. It will depend on the number of fans you need – a typical unit can serve up to four wet rooms, for example, kitchen, utility or bathrooms).

A PIV system should be significantly cheaper than this at about €1,200 – €1,500 but, to my mind, would be less satisfactory as it pushes cooler attic air into the house and forces air changes through the gaps in the walls and floors and so on.

It is important to understand that no house should be entirely airtight. That would be unhealthy. Instead a house should have controlled levels of ‘planned ventilation’ instead of leaks and draughts throughout. This is difficult to achieve on an existing 1970s house unless undertaking a deep retrofit.

While hard plaster on walls is quite airtight, your windows will most likely be quite leaky. Your floors and attic may also be ventilated which often leads to draughts within heated spaces. To achieve decent levels of air-tightness usually involves replacing windows, using membranes on the floors and external ceilings which means re-plastering and re-wiring too.

I know that the above might not be exactly what you wanted to hear. However, once the source of the problem is clear the solution will follow more easily. As always I would highly recommend that specialist advice is sought from a local registered architect who has inspected your house. Often the problem may be from a number of interrelated issues which all need to be addressed for a successful outcome.

If you are considering changes to your home, work with a registered architect. Find one on riai.ie, the registration body for architects in Ireland.

Alan Burns, MRIAI, is a registered architect and co-director of Bright Design Architects; brightdesigns.ie

Do you have a design dilemma we can help you with? Email [email protected]Advice provided is for guidance only and readers are advised to seek professional assistance for any proposed project.

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'The stove you select depends not only on the type of build and level of insulation of your home, but on the type of fuel to be used'

‘The stove you select depends not only on the type of build and level of insulation of your home, but on the type of fuel to be used’

Q: My wife and I have just purchased our first home and it comes with a space for a fireplace stove but it has been left to us to choose and install. What are the options available and are there any other decisions and issues to consider?

A: Fire in the home has been a ‘must have’ since the dawn of mankind. The need for heat, light and the mesmerising flicker of the flame has always drawn us to fire, especially at this time of year. However, the once simple decision to install a fire has never been so complicated, particularly when energy efficiency and our carbon footprint are considered.

The open fire has all but been extinguished in new houses, and the accepted norm more often than not is its room-sealed or glass-fronted cousin. The stove you select depends not only on the type of build and level of insulation of your home, but on the type of fuel to be used. Different considerations will apply to a new build versus a retrofit and to gas versus solid fuel.

Location is the first decision to make. Your investment needs to deliver not only warmth but that ”wow” factor. Selected and placed correctly, a stove can transform a room. It can provide a missing focal point or open up the potential of a neglected corner. However, put it in the wrong place or size it incorrectly and it may compete with a television for attention, and often provide too much or too little heat.

The next decision is to choose the type that is right for you and your lifestyle. While chimneys may be great for Santa, they are equally great for unwanted heat loss and draughts. With modern new house constructions being reliant on insulation and air tightness, this is a challenge that a room-sealed appliance can overcome.

Solid fuel versus gas is the next conundrum. Often you will have no idea what type of house you want, but be in no doubt that you want that house to have a log stove. A log stove will certainly give the best heat output and is more eco-friendly than gas but it comes with baggage.

Firstly, you will need a good supply of quality kiln-dried firewood and plenty of dry storage space close to the fire and elsewhere. While you might be imagining a wonderful crackling fire, don’t forget the labour involved with ash removal. In a modern insulated home, the output from a log fire can easily overheat a room and, generally, it can’t be turned down or off – the real effect of modern insulation and airtightness are often overlooked.

On the other hand, gas is less labour-intensive and you can exercise a greater degree of control with lower heat outputs. Gas also has the benefit of a balanced flue that can use a chimney or go horizontally out through a wall like a boiler. This means that it can often be located away from an external wall and freed of the constraints that come with a chimney which requires height for a good ‘draw’. The range of styles and models to choose from are also extensive – for example, freestanding or built in. However, as gas is a fossil fuel, it does nothing to help the environment or your carbon footprint. Bio-ethanol and electric flame-effect fires are also low heat alternatives to solid fuel or gas and do not require a flue or chimney. The most important consideration, though, is safety. With air-tight buildings, the requirement for ventilation becomes vitally important. Fires need oxygen and will starve a room unless provided with a direct air supply or dedicated room vents.

Equally, a carbon monoxide alarm is essential. Solid fuel fires also require non-combustible hearths to protect against sparks, just as a traditional fire does. Current building regulations take all of the above into consideration and your chosen installer should take this into account and provide certification of safe installation on completion. A full survey by a specialist supplier will advise on these issues in advance to give an accurate quote for the works before proceeding.

Finally, and to recap, choose the type of stove to suit the location, your lifestyle and the level of heat needed. Engage the technical advice of a specialist and think safety.

Alan Burns, MRIAI, is a registered architect and co-director of Bright Design Architects; brightdesigns.ie

If you are considering changes to your home, work with a registered architect on riai.ie, the registration body for architects in Ireland.

Sunday Independent

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