Existing Lined Wall Cavity Insulation


You don’t need to remove linings to insulate existing lined wall cavities. These can be insulated by drilling and filling holes through the external or internal lining with either a water repellent dry fibre or wet foam system. With either wall insulation system there are usually 3-4 holes of 25-30mm drilled in the height of the wall, about every 500mm around the building. Unplastered or unpainted brick veneer cavities should not be insulated with either system, due to the high potential of wind driven rain entering such unsealed cavities. Total R-value (installed) of R2.1 -R2.6 is achieved in a typical 90-100mm wall cavity with water repellent dry fibre or R1.0 – R1.5 with wet foam system installed correctly.

The ONLY currently available dry water repellant mineral fibre insulation system is formaldehyde-free CosyWall insulation, which must be installed at the design density to prevent settlement and ensure Total R-value is achieved and maintained. With the Cosywall system holes are plugged immediately after insulation is installed with filler, then sanded, primed and finish coated.

drilling_pattern finished_wall

CosyWall water repellent dry mineral fibre system tests indicated no wicking after 30 days and no settlement after 6 months at the design density. CozyWall insulation prevents potential fire spread in the cavity and reduce noise transmission through the walls.

Qmulus_testingWet foam systems are usually manufactured on site from urea formaldehyde chemicals & water, or occasionally urethane foams. Installation of these systems is more complex, which often means long term Total R-values (installed) considerably less than that stated by suppliers.

The wet foam process requires 25-30 days full home ventilation to aid curing and reduce formaldehyde levels. Ideally, the home should not be occupied during this period. External wall hole plugging should not be completed until full curing is complete and internal wall moisture content is less than 24%. Serious concerns about the suitability of wet foam for existing wall cavities have been raised by Department of Building & Housing (Determination report 2008/35) and BRANZ (reports SR233 and SR234), which are available on their respective websites.

wet_foamWet foam holes should be plugged with a glued timber plug, then filled, sanded and primed. Finish painting should be delayed until all moisture introduced with wet foam has evaporated.

Branz report SR233 states 6% perimeter and thickness shrinkage from framing timber as the foam cures – which reduces the manufacturers claimed R2.9 to a total R-value (installed) of R1.0 – R1.6

Wet foam systems can reduce potential fire spread in the wall cavity (depending on edge gap extent) and act as a cavity noise absorber.