An exposed single skin masonry wall such as a concrete tilt slab internally insulated with non-combustible DCT VulcanWool stonewool insulation separated from the masonry by a drained and/or ventilated cavity. The ProctorPassive SmartVap must be taped and sealed to form a continuous air and vapour control layer to reduce internal moisture vapour from reaching and condensing on the masonry. This solution is a rarely used compromise where external insulation is not an option. This solution is a high risk strategy that relies on the perfect installation of the internal control layer and the effectiveness of the drainage cavity. Continuous mechanical ventilation to manage indoor moisture loads will be required in most climates. An independent hygrothermal calculation in accordance with AIRAH DA07 must prove suitability.