This phenomenon is caused when water vapor in air within the fabric of a building’s walls, floors, ceilings or roof condenses into liquid water. Interstitial condensation is a serious risk and can cause significant structural damage, rot and corrision leading to mould growth, dry/wet rot, fungal decay and insect infestation.
Interstitial condensation is caused primarily if moisture laden heated indoor air can ingress freely into the building fabric and then be subjected to temperature change. Therefore external walls, especially solid non cavity walls, and walls with in built natural ventilators (air bricks, passive vents) are the highest risk areas of any building, which is most common in older buildings. Cold or thermal bridging creates risk of interstitial condensation even in new builds especially if insulation performance is interrupted or inconsistent.
Interstitial condensation is simply and easily prevented by ensuring no pathways or routes for air to ingress or heat to transfer exist and ensuring insulation characteristics provide complete coverage.
It must be noted there is an enduring myth in official ventilation guidance that suggests interstitial condensation can be caused by positive pressure ventilation systems. This myth has endured for over 2 decades and has caused many stakeholder groups on the specification side of the industry to distrust such strategies. The myth claims positive pressure ventilation systems force moisture laden air into the building fabric and therefore directly cause interstitial condensation. The reality is the myth is exactly that – just a myth. The reality is there have been millions of positive pressure ventilation system retrofits across Britain since the strategy was originally created in the early 1970s and there is no in-the-field evidence to support the myth. Certainly, at Better Indoors we have never seen any such outcome in any of the 15k+ positive pressure solutions we have designed, supplied and installed across Britain since 2013.
The fact is positive pressure ventilation retrofits are just one of a number of key features that make up a successful relative humidity problem solving retrofit. The problems come when solutions are poorly designed and installed by inexperienced, unqualified stakeholders and contractors, especially those who think all you need is to install a PIV unit somewhere and turn it on. There is so much more to it than that.
At Better Indoors our retrofit designs never result in interstitial condensation or any other consequential problems and always permanently address the root cause of condensation and mould. Book a survey today.
