Can I use positive input ventilation with internal wall insulation? – Can I Just Ask? | Ep.45

In this episode, Chris and Andy look at why positive input ventilation (PIV), despite being widely used in retrofit projects, generally isn’t recommended alongside internal wall insulation (IWI). Andy explains that PIV works by pressurising the indoor space to push fresh air in, but this same pressurisation forces moisture laden stale air out through gaps and cracks in the building fabric. With IWI schemes, where conductive components sit on the cold side of the insulation, that moisture can condense on cold surfaces out of sight, leading to mould growth and material decay over time. The conversation moves on to better alternatives, including MVHR (whether decentralised or single room) and extract ventilation, both of which avoid forcing air into the fabric and reduce the condensation risk associated with PIV.