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 openess.
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 buildingDuring 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.