Exterior wall insulation, also known as external insulation, is a method of insulating your main walls from the outside. It is most commonly used in homes with solid walls that are free of cavities.
The majority of UK homes built between 1920 and 1925 will have solid walls.
It is therefore more difficult to insulate walls because there is no cavity in which you can add blow-in insulation.
It is possible, although it may be more difficult than you might think. There are two options for insulating solid walls.
Insulation for the interior walls – This insulation is used to protect the inner surfaces of the exterior walls of your house.
Exterior wall insulation – This is another obvious area, but it is where insulation is applied on the exterior surface of main exterior walls.
This article will focus on external wall insulation. It is possible to choose external insulation over internal insulation. Let’s also discuss the main benefits and drawbacks.
How can you tell if your walls are cavity or solid?
If your home is located in the UK, and was built between 1920-1925, it will most likely have solid walls.
This is the easiest way to verify it visually. If you have un-rendered brick walls, and can see the sides as well as ends of the bricks, then you have a solid brick wall.
If you have rendered walls, you will need to measure their thickness. This can be done easily at a window or door opening. It should be between 230 and 250mm. However, some older cavity walls measured 250-270mm. A modern cavity wall is 300mm.
Don’t assume all walls are equal. My house has both 250mm solid brick walls and 600m solid stones walls.
Exterior wall insulation: Why might you need it?
These are the main reasons to go down the exterior wall insulation route:
Your walls don’t have any cavities to insulate. This is very common in older homes.
Insulating internally won’t cause you to lose any floor space. Instead, you would need to insulate the outer walls of your main exterior walls. This is typically done by building a wooden frame and then installing rigid foam insulation. Then you would finish it with plasterboard and a vapour barrier.
This would mean that you could lose between 100 and 150mm of floor space depending on what insulation you choose and the u value you set. If the room is connected to more than one wall, you will lose that floor space.
If you have large rooms, this might not be an issue. However, if you have small rooms in your home it could make a huge difference.
You want to minimize cold bridging. Cold bridging occurs when cold passes through your walls from the outside to inside. Masonry is a great conductor of heat, so cold can pass through walls quickly.
Cavities were created to minimize this because cold water cannot cross the cavity. Insulation and air are better heat conductors than masonry.
Cold bridges are possible even within cavity properties. Cold bridges, such as at sills and window heads, can be formed to allow cold to pass through the cavity.
External insulation from PD Rendering & External Wall Insulation reduces cold bridging by wrapping the house with one large sheet insulation. This insulation separates cold air from masonry walls, reducing the likelihood of cold bridges. It is a bit like wrapping a coat around your house.
However, internal insulation allows for some cold bridges to be left at wall junctions and other locations.
The thermal mass of your main walls should be used to your advantage. It is almost like a storage heater. If your main walls were insulate internally, you would keep the heat inside. This means that masonry walls don’t heat up.
The large thermal mass of masonry walls heats up slowly if they are insulate from the outside. After your heating is turned off, the walls will slowly release the stored heat. Because there is insulation outside the wall, most of the heat is redirected back inside the house.
You are looking to renovate/renew your exterior and increase its thermal efficiency. The method of installing exterior walls insulation means that your home will have a new rendered brick slip finish.
If your walls are in good shape, the exterior wall insulation is chemically or mechanically bonded to them. They are then typically finished with an acrylic or rendered finish.
These finishes can be mixed with colour pigments so you don’t have to paint your exterior. This alone will save you money on future redecorating.
Exterior wall insulation has many advantages
Exterior wall insulation has many benefits, so I will just briefly list them here.
Avoid cold bridging
You won’t lose valuable internal floor space.
Let’s make the thermal mass of walls work in heat sync.
This will make your home look brand new from the outside.
This can reduce future redecoration expenses.
This increases the efficiency of your home’s heating system.
Exterior wall insulation has its disadvantages
External insulation can be expensive. The last estimate I saw was about PS100/m2. It is usually twice as expensive to insulate internally. However, internal insulation will not be free. This includes extra costs like moving radiator pipes away from walls, replacing flooring and redecorating.
When deciding whether exterior wall insulation is right to you, there are many things to consider.
Do you consider maintaining an internal floor space a priority?
Are you able to afford it?
It might be a good idea to make your house more attractive and save money on future redecoration. You might also be thinking about insulating your home internally.
I believe exterior wall insulation is more beneficial than internal insulation. The only downside (and it’s a biggie), is cost.
However, internal insulation can be more expensive than external insulation if your home’s interior is well-maintained.
If you are concerned about cost, talk to your installers. They should be able tell you if grant assistance is available in your region.