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You don’t need to remove linings to install existing lined wall cavity insulation. 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 three to four 25-30mm holes drilled in the wall, about every 500mm around the building.
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.
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.
The ONLY currently available dry, water-repellant, mineral fibre insulation is the formaldehyde-free CosyWall system, which must be installed at the design density to prevent settlement and ensure that the Total R-value is achieved and maintained. With the CosyWall system holes are plugged with filler immediately after the insulation is installed, then sanded, primed and finish coated.
CosyWall water-repellent, dry, mineral fibre system tests indicated no wicking after 30 days and no settlement after six months at the design density. CozyWall insulation prevents potential fire spread in the cavity and reduces noise transmission through the walls.
Wet foam systems are usually manufactured on site from urea formaldehyde chemicals and water, or occasionally urethane foams. Installation of these systems is more complex, which often means long-term that the Total R-values (installed) are 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 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.