Most membranes promise good water tightness. But for how long?
Whether underlays are supplied as single layer or multi-layer, it is the functional layer which takes care of windproofing, waterproofing and vapour openness.
An underlay serves a vital secondary water shedding function
- To protect the building from rainwater penetration
- To allow water vapour to escape from the construction and avoiding condensation
- To contribute to air sealing the wall and reduce ventilation heat losses thus promoting thermal performance of the building
| However resistant to tearing or elongation during installation a product may be, it can take only a few weeks for the key functionality of watertightness to be degraded.The main factors impairing the effectiveness of an underlay are UV and heat. |
| UV damage during the construction |
| Before the roof is covered, an underlay can suffer from the UV radiation of sunlight. Prolonged UV radiation can cause the polymer to become brittle. |
| Heat damage during the lifetime of the building |
| During the life of a building, unexpectedly high temperatures may build up onto a roof underlay on top of the thermal insulation. At times, these temperatures may even exceed 80°C. |
| These unexpectedly high temperatures can have a major impact on the ageing of an underlay and hence its effectiveness. |
| Direct UV exposure can impact a product functionality irreversibly. Not visible at “day one”, it can impact product performance over the long term, especially when combined with the slow but continuous impact of heat. Watertightness is a property that is crucial to preserve. |
Tyvek® proven durability
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