SR436 Linings-on retrofit insulation in weatherboard walls: Ensuring effective water management (March 2020)

There is a clear need to provide easier means to insulate walls in New Zealand, given the number of houses in the stock that remain uninsulated. Loose-fill insulation is one possibility for satisfying this need. The aim of this research was to technically assess potential solutions for linings-on retrofit solutions in New Zealand and understand any associated risks. Of primary concern was that any solutions do not cause damage by water ingress.

This research has shown that both bonded and loose-fill insulation can be installed behind an underlay and not lead to increased water transfer. This provides great scope for the widespread retrofit of New Zealand walls. The research has also shown that, without an underlay present, water transfer can occur, irrespective of whether the insulation material itself is hydrophobically treated. It does appear possible, however, to create installed insulation that resists moisture transfer to the inside of the wall.

See the BRANZ Research Now fact sheet for a short and accessible summary of this report.