People increasingly asking for advise on insulating their house, I always tell them that external insulation is way better than internal insulation. One of the main reasons for this is that there are a lot of risks that come with internal insulation, risks of mould growth behind the newly insulated walls because the dew point was moved inwards and moisture from inside the house starts condensating on the cold inside of the external wall. The presence of Cellulose Battens usually gives mould a really nice lunchtime.
The danger of mould Growth in Ireland is heightened by the fact that we are in Island nation with high relative humidity and poor internal ventilation
External installation on the other hand is very good, you have the opportunity to minimise thermal bridges and should be done in conjunction with new windows. We always recommend passive windows and about 150 mm of external insulation. If you have an old stone wall you need to look at breathable insulation.
In our latest project we are hanging the triple glazed windows halfway out over the blockwall for support. We've taken out the concrete sills and we have replaced these with Passive Sills made right here in Cork. In this particular project we are using triple glazed passive windows. We get these delivered from Munster Joinery within six weeks of measurement, and we get the builders to fit them tight. I avoid getting Munster Joinery to fit.
You will see that we tape the exterior of the window back to the exterior of the block wall with the weather tape. This is to minimise or eliminate draughts. We then tape the interior frame of the window back to the plaster wall to give us a very strong airtightness seal.
Because in retrofit it tends to be quite invasive to dig up the ground floor internally, one of the strategies that we take is to dig a trench around the perimeter of the house externally because we have to move a lot of the drains out from the wall to accommodate the new insulation. In doing this we dig down so we can put in a different type of insulation that avoids moisture moving upwards. The reason for doing this is to stop flanking heat loss from the external soil to the internal floor. In general in very old stone buildings we have tended to take up the internal floor because of issues with rising damp.
In this external insulation application, which was carried out by Grainger insulation, we have avoided work to the interior of the building. In stage two we will be extending and changing the roof so we be able to fully insulate roof spaces and make them connect with the external installation at the eaves.
After all of the passive measures we look to install active measures to meet the residual heating demand for the house. This is where we use a heat pump. No heat pump is a bit like a reverse fridge. It makes hot water out of cold air by compressing the air with a refrigerant. Heat pumps are really efficient. Your oil or gas boiler costs €1 and you get 90 cent of heating out of it. That makes it 90% efficient. A heat pump in a well insulated house can be 500% efficient meaning that for every year are you put in you get €5 of heat out of it. That would mean that if your oil bill was €1000 a year, a heat pump should cost you about €200 a year to run. And efficient heat pump runs at about 25°C, a normal radiator on oil or gas usually runs at about 65° C. This means that if you are using a heat pump you generally need larger or more efficient radiators and you're running the heating more constantly rather than in bursts. The benefit of this is you have a constant level of heat in the house which actually mitigates against condensation and mould growth. There are two bits to a heat pump, the inside and the outside bit. The inside one can be about the size of a large fridge, or it can be a complete mess of gear that takes up a lot of space.
Outside part of the heat pump-my advice is keep this close to the house but not up against the back wall as you may get a small degree of noise or vibration. Short travel distances for the heating pipes reduces heat loss.
Inside part of the heat pump-this is a messy one from Grant where all of the elements or not tidily contained. This is actually quite an efficient piece of kit it's just messy.
Inside part of the heat pump-this is more tidy installation from Daiken.
In the last few jobs that we've done the heat pump this cost between €8500-€11,000. You have to add on to this the cost of new radiators which can typically cost up to €4000. You do get a grant of €3500, you will also have to get a technical assessment and a BER to make sure you qualify which could cost you €500, still worth it if a bit of a pain in the ass.
Now with the insulation done, externally, new windows, the heat pump and low-temperature radiators you have a super efficient building. If you want to go to whole hog I would spend about €10K on PV panels, which make electricity from the Sun all year round. During the summer you can sell excess electricity back to your supplier. The solar panels work really well when you have a heat pump because your solar energy can replace that euro you are sticking into the heat pump.
Is this expensive? Yes! Depending on the size of the house external installation could be between €16,000 and €24,000. The SEAI grant is €8000, but if you've previously got a grant for cavity insulation then you won't be other get this grant which seems crazy. A heat pump as I mentioned before is between €8500 and €12,000 depending on the size of your house. New radiators could be about €4500 thousand euros. New windows are a large expense. We have found that they've come in around €10,000 on an existing house or less. If you're doing an extension with a large amount of glass obviously that price will go up. Munster Joinery do a really good passive aluclad window made in Cork and are a pretty good price. My advice is don't get them to fit the windows and make sure they measure them very tight to the opening. Get your builder to fit the windows. These are all individual actions that you can take but obviously there is a one stop shop available from the SEAI. I am rather sceptical about these companies because I'm yet to receive a callback from any of them . .
Deep retrofit in general can cost around €65K but I do find that there are a lot of people very eager to do this especially in the context of higher heating and electricity prices. In general you should expect grant aid of about €15k to €20k going the individual route.