A vapour barrier is very important for a flat roof – it protects the insulation against moisture from inside the building. In this way, the vapour barrier prevents the appearance of damp stains, leaks, mildew and damage to the roof structure. But which vapour barrier should you ideally choose? And what do you need to bear in mind when installing it? Find out more by reading this article.
Protecting the warm side
A vapour barrier protects the insulation material against moisture present in the building. It is therefore only logical that this vapour barrier should be fitted to the warm side of the insulation, which is the surface facing the interior space. The vapour barrier serves several important purposes in this part of the building:
- The vapour barrier makes the roof airtight
- It ensures that water vapour cannot attack the insulation
- It maintains a consistent insulation value
- A vapour barrier can also be used as a temporary rainproof covering during construction work
Which vapour barrier should I choose?
The choice of vapour barrier depends mainly on the air humidity level inside the building. It goes without saying that, in this respect, there is a big difference between a car dealer showroom and a swimming pool. Not all types of buildings need the same moisture protection on the warm side of the construction.
The different air humidity levels in the interior climate are subdivided into four categories:
| Indoor climate class | Description | Examples |
| I | Buildings with little or no permanent moisture production | – Showroom – Warehouses for dry goods |
| II | Buildings with limited moisture production per m³ and with good ventilation | – Sports halls – Large homes – Shops |
| III | Buildings with substantial moisture production per m³ and with moderate to sufficient ventilation | – Buildings with RH < 60% – Small homes – Restaurants – Hospitals – Buildings with limited air conditioning |
| IV | Buildings with high moisture production | – Buildings with RH > 60% – Swimming pools – Moist production and storage halls: laundries, breweries |
*RH: Relative Humidity – Source: TV 215 Table 12
High quality expertise makes it easier to choose the right vapour barrier
Is there another vapour barrier that is suitable for every interior climate class? No, definitely not. In fact, the most important thing is that a vapour barrier is fitted professionally and according to the current standards. Only a vapour barrier that is perfectly fitted can guarantee the following properties:
- Maximum protection for the insulation material
The insulation is fully “sealed” between two waterproof bituminous layers. The vapour barrier and under-layer must also be perfectly connected to each other. - A fully waterproof vapour barrier
The longitudinal and transversal coverings of the vapour barrier must be given a waterproof finish by the roofer. - The vapour barrier adheres perfectly to the support
A vapour barrier that adheres perfectly to the support is not only important when it comes to avoiding moisture problems. It is also important for wind resistance across the entire roof.
If the vapour barrier meets the above conditions, it is easy to choose the right one:
| Interior climate | Vapour barrier |
| Climate class I – III building | 3 mm thick reinforced bituminous membrane |
| Climate class IV building | Bituminous membrane covered or reinforced with an aluminium layer |
An ALU-reinforced vapour barrier enables a building to stand the test of time
For this reason, a vapour barrier with additional aluminium protection is only strictly necessary for an interior climate class IV building. But it would certainly not be a bad idea to opt for an ALU-reinforced vapour barrier with additional protection for other buildings. At the moment, you may not know how the building will be used many years from now. For example, a dried fruit warehouse might later become a humid production hall. By opting for an ALU-reinforced vapour barrier, you can keep all options open for the building in the future.
As part of the IKO range, you can choose from five ALU-enhanced vapour barriers:
| Self-adhesive vapour barriers (E4) | |
| IKO shield ALU/SA 50m | Cost-effective membrane for industrial roofs; low fire load |
| IKO shield PLUS ALU/SA 25m | User-friendly membrane for application on steel and timber decks |
| IKO shield PRO ALU/SA 20m | Robust and all-round membrane for heavier work |
| Vapour barriers for torch on applications (E4) | |
| IKO shield ALU3 T/F | User-friendly, suitable for short period temporary waterproofing |
| IKO shield ALU4 T/F | Heavy duty, suitable for short period temporary waterproofing |
Selecting the right vapour barrier
Would you prefer to opt for an aluminium-free vapour barrier? In this case, you should choose one that is sufficiently sturdy and will not yield. This is especially important when fitting a vapour barrier to a rough support or construction with interrupted surfaces.
All IKO vapour barriers that are self-adhesive or have a polyester reinforcement can always be used.
A few more tips
- For renovation work, the existing bituminous waterproofing may act as a vapour barrier.
- On interior climate class IV buildings, the vapour barrier cannot be perforated. Mechanical fasteners cannot be used.
- Are you using insulation panels fitted with an aluminium layer? In this case, you must also fit a vapour barrier.
It is vital that you fit a vapour barrier on all flat roofs. Different moisture levels exist in every building and this can lead to unpleasant problems with dampness. Having a hermetically sealed vapour barrier fitted by a professional enables you to avoid a variety of problems.
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