External insulation of the facade is the most effective way to re-insulate the building’s external walls. But it’s a big process – read here what you need to be aware of.
When can external insulation of the facade be a solution?
In general, external re-insulation of external walls is a good solution for old buildings with massive external walls, or where cavity wall insulation cannot be done due to limited space in the cavity wall. The method is also used on newer buildings with poorly insulated external walls made of brick, aerated concrete, or concrete. Remodeling or major renovations, which involve new facades or a new roof, can reduce the energy consumption of these houses.
If there are problems with moisture in the existing facade, these can often be solved in connection with external insulation, just as the external insulation prevents problems with moisture and mold, which can otherwise arise with internal insulation. In addition, problems with the thermal bridges are also solved, as these will disappear with an external retrofit.
On the other hand, external facade insulation will typically not be the solution if, for example, you have an older property with fine and detailed facades or live in an area where it is prohibited to change the facades. External facade insulation can cause a significant change in the appearance of the house, so the technical and practical advantages must be weighed against the architectural considerations.
What are the advantages of external facade insulation?
If you choose to insulate the outside instead of the inside, the method is approx. 30 percent more efficient. In the case of internal insulation, there are internal walls that cross the external walls, as well as other parts of the structures that will continue to function as thermal bridges.
The existing outer wall is kept warm and dry, and the risk of moisture problems is minimized. The old and cold outer walls will act as a heat depot during the heating season and help keep the house cool in the summer.
An old, run-down facade is improved by insulating it from the outside. If, for example, the building’s masonry joints are broken down and damaged, or the facade plaster is cracked, you can kill two birds with one stone by insulating from the outside and thus avoid the facade renovation.
The insulation does not take up space in the interior spaces, so the living area remains unchanged. Installations such as heating pipes, radiators, and electricity as well as stucco and other things are not affected and do not have to be moved, as they otherwise have to with internal insulation. Since the work can take place without affecting the interior rooms, you avoid the trouble of cleaning the rooms and dust and dirt in connection with the work.
What are the disadvantages of external insulation?
External insulation is a rather expensive solution that must be carried out all at once, while internal insulation, which is less expensive, can be carried out gradually room by room. However, in contrast to external insulation, there are costs for both plumbers to move radiators and the electrician to move plugs out.
It certainly doesn’t have to be a disadvantage, but be aware that the appearance of your home can change with external facade insulation.
It may require a little more work when the facade is insulated from the outside – for example, it may be advantageous to move windows and doors further out so that they do not sit too deep – this can result in a poorer incidence of light and give a slightly strange appearance. Therefore, it may be a good idea to insulate the facade at the same time that the windows and doors are replaced so that they can be positioned so that they fit together with the new facade. The roof overhang may also be too short, so it may be necessary to extend the roof. Read more below.
It can be difficult to see what external insulation will mean for the building, both technically and architecturally, so it is definitely recommended to take an architect along for advice in the planning.
An adviser can also make calculations that show how much you can save on heating costs and how quickly the investment pays for itself. The adviser can also assess how thick a layer of insulation it is energy-wise to choose. The construction work should be carried out by professional craftsmen.
How will exterior facade insulation affect the appearance of the building?
As mentioned, the thicker facades will mean that the original windows and doors will sit further inside the wall holes, which can give the building a somewhat fortress-like and clumsy feel, and it can also provide less daylight inside the home.
If the insulation is carried out in connection with a major conversion and renovation, the new windows should be placed further out in the facade. If the original windows are to be preserved, they should be moved further out in the facade, especially if a thick layer of post-insulation is involved. Moving doors and windows will also mean that the frames cover the joint between the outer wall and the insulation layer, where cracks often occur because the new and old materials move differently.
If there is more than 50 mm of insulation on the outside, it is typically necessary to move the windows out. The typically used insulation thickness is 100 mm, but some choose to set up up to 250 mm.
Remember to move downspouts away from the wall at the external facade insulation. The same may apply to lighting or external sockets.
Problems with the roof overhang
Unless there is a large overhang on the building, the thicker outer walls can cause problems here, as the overhang can be too small, so it looks wrong, and as a result must be increased. Please note that if the roof is made of tiles, it must be decided whether the roof should be extended by 1 or 2 tiles.
The purpose of the roof overhang is to protect the underlying facade and windows against moisture from rain, just as it shields from the sun. If the building has a small overhang, a large amount of insulation in the external insulation can cause problems, as rafters and the like must also be extended if necessary.
If the additional insulation is done in connection with a major renovation, where the roof is also replaced, it will normally be unproblematic to extend the roof a little, possibly at the same time that it is raised a little, to also make room for more insulation in the roof.
What is the price of facade insulation?
The price of exterior facade insulation depends on which method and which finish surface you choose.
Do you have to apply for permission from the municipality before you re-insulate external walls?
Whether you need to apply for a building permit for additional insulation in the municipality depends on rules in the local plan that relate to the appearance of the building, and you should therefore always speak to the municipality’s technical administration.
Which solutions can you use for external post-insulation?
There are different systems and methods for external insulation from different manufacturers, but the basic question is whether the new facade should be plastered or have a covering of e.g. wood or fiber cement boards.
The thicker the insulation you choose, the more you will save on heating costs, but constructive and architectural considerations will usually set a limit to the thickness of the insulation layer.
Is facade insulation a do-it-yourself task?
Exterior re-insulation is not a job you should do yourself unless you have a craftsman background. It is important to ensure that the various layers of the construction are done correctly. However, you can handle the processing yourself.
Sketch of post-insulation with cladding:
Subsequent insulation with a light sheet or board cladding
Basically, the solution consists of posts made of pressure-treated wood or steel profiles being mounted on the existing facade. Between these, the insulation is mounted in the form of rolls or batts. If there are to be several layers of insulation, the next layer of battens is laid so that they cross the first to minimize thermal bridges – between these, the next layer of insulation is installed.
On the outside, a layer of wooden covering such as cedar or larch is mounted on tiles, but it can also be covered with other cladding. Under this a windproof layer in the form of windproof cardboard or windproof plaster. The outer covering itself is mounted on spacer strips to ensure that it is adequately ventilated behind. The ventilation gap must be secured with an insect net against pests such as insects, mice, and rats.
In order to break the thermal bridge at the transition of the wall to the foundation, the insulation is continued down in front of the plinth between 300 and 600 mm below ground level with, for example, a cladding plate of e.g. eternit on the outside. When you are already underground, it is a good idea to consider making a volume drain.
It is typically recommended to perform this plinth insulation with non-water absorbent insulation such as polystyrene. The work must be carried out very carefully and correctly – not least the joints at the eaves and around doors and windows.
Facade insulation with plaster
There are different systems for post-insulation with plaster. What they have in common is that special facade batts, which are able to support the layers of plaster, are attached directly to the existing external wall both with adhesive mortar and dowels. After this, a layer of under-plaster with embedded reinforcing mesh is applied as reinforcement.
The final layer of plaster can be smooth or textured. The plaster layer can be colored or can subsequently be treated with a suitable diffusion-open paint, e.g. silicate or silicone paint.
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